xxl pressure and moments unit guide - physicslocker...the concept described here where the forces...

XX Unit guidePressure and moments

Sheet 1 of 1© Harcourt Education Ltd 2004 Catalyst 3This worksheet may have been altered from the original on the CD-ROM.

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Where this unit fits in Prior learningThis unit builds on:unit 7K Forces and their effects and links to unit 9K Speeding up. Work on muscles as levers relates tounit 9B Fit and healthy.This unit provides opportunities to revisit and revise topics met in other units, e.g. forces, particletheory. With some pupils, teachers may wish to concentrate on some of the new topics, extendingactivities, and with others to spend more time on revision of previous work.

The concepts in this unit are: pressure, moments.

This unit leads onto: further quantitative work on forces at KS4, for which it provides the foundation.

To make good progress, pupils starting thisunit need to:• be able to identify the directions in which

forces act and represent these by arrows• be able to calculate surface area of simple

shapes• know how muscles in the body are

attached by tendons and producemovement by contraction of antagonisticpairs.

Framework yearly teaching objectives – Forces• Recognise how the turning effect of a force (moment) is related to the size of the force and the distance the force is from the pivot; use moments

to explain how a simple object can be balanced.• Recognise how the effect of a force depends upon the area to which it is applied and that the force acting per unit area is called pressure; use the

relationship to explain: the pressure exerted by solids; the pressure within liquids and gases.

Expectations from the QCA Scheme of WorkAt the end of this unit …

… most pupils will … … some pupils will not have madeso much progress and will …

… some pupils will haveprogressed further and will …

in terms of scientific enquiry NC Programme of Study Sc1 1b, c, 2c, g, i, j, k, l, m

• plan an investigation into balance, making sufficient observationswith precision

• identify a pattern in their results and use this to draw conclusions,relating these to the principle of moments.

• make systematic observations ofbalance and use these to drawconclusions.

• account for anomalies in theobservations of balance andevaluate their conclusions byreference to the principle ofmoments.

in terms of physical processes NC Programme of Study Sc2 2e; Sc4 2e, f, g

• summarise key ideas about pressure• use the relationship between force, area and pressure between solids

and within liquids and gases• explain the action of levers, including examples in the human

skeleton in terms of the turning effect of a force• use the principle of moments to explain balance and give examples of

its application, e.g. crane counterweight.

• describe how force can be ‘spreadout’ to reduce pressure or ‘focused’to increase pressure

• recognise that the turning effect ofa force can be increased byincreasing the length of the leverarm and give a use of this

• describe how to balance a seesaw.

• use the definition of pressure incalculations to explain theoperation of a range of devices

• relate hydrostatic pressure inliquids and gases to density

• apply the principle of momentsto explain a range of situations,including the action of levers.

Suggested lesson allocation (see individual lesson planning guides)Direct route

L1Under pressure

L2Taking theplunge

L3Pressure inthe air

L4Where’s thepivot?

L5Balancing act

L6Moments inlife

L7Getting balanced –Think aboutequilibrium

Booster 5Focus on forces –Forces all around

Extra lessons (not in Pupil book)

L7 Getting balancedExtra time forActivity L7a.

Review and assess progress(distributedappropriately)

MisconceptionsPupils might confuse the terms ‘force’ and ‘pressure’. Avoid saying the pressure is concentrated instead of the force is concentrated. When pupilshave grasped that the same force spread over a larger area decreases the pressure, they can still become confused when dealing with numbers andforget that doubling area halves the pressure.

Additional informationPressure is technically a hydrostatic process, i.e. the forces act in all directions. The concept described here where the forces act in one direction isactually ‘stress’.It is acceptable to use the units N cm–2 for example for the ‘hands and feet activity’ because the conversion is difficult (1 Pa = 1 N m–2 = 0.0001 N cm–2).To avoid conversion, use N cm–2 where more appropriate, although pascals might be useful.

Health and safety (see activity notes to inform risk assessment)Risk assessments are required for any hazardous activity. Pupils may learn safe handling techniques for heavy loads.

J-L-Unit Guides.qxd 22-Jun-04 4:20 PM 3


L1Lesson planning

guideUnder pressure

Suggested alternative starter activities (5–10 minutes)

Introduce the unit

Unit map for Pressure andmoments.

Learning objectivesi Pressure depends on the force of an object and the area over which the force is spread.ii For a given force, if the area is bigger the pressure decreases, and if the area is smaller the pressure increases.

Scientific enquiryiii Predict what the pressure will be in different situations. (Framework YTO Sc1 9f)

Learning outcomes

Share learningobjectives

• Define what pressure is.• Describe how the force

and the area over which itacts change the pressure.

Problem solving

Show pupils the scenario ofa child falling through theice. Pupils discuss how alarge adult can rescue thechild.

Word game

Play a game of hangman toremind pupils of forcesknowledge from Year 7.

Capture interest

Give some pupils twowalnuts each and ask ifthey can crack them withtheir hands.

Suggested alternative plenary activities (5–10 minutes)

Review learning

Show video clips of highand low pressureapplications.Catalyst InteractivePresentations 3

Sharing responses

Having calculated pressure of shoes with Activity L1a,pupils do this for snowshoesor stilettos, and compareresults.

Group feedback

Pupils look at differentfootwear used for ActivityL1a and discuss in groupshow this changed pressure.

Word game

Write a poem, e.g. a haikuor kenning, or a limerick,about pressure.

Looking ahead

Work out the pressure dueto weight of water on thebase of a fish tank.

Suggested alternative main activitiesActivity

Textbook L1

Activity L1a Practical

Activity L1b Paper

Learningobjectivessee above

i and ii

i, ii and iii

i, ii and iii

Description

Teacher-led explanation and questioning OR Pupils work individually,in pairs or in small groups through the in-text questions and thenonto the end-of-spread questions if time allows.

Foot pressure Pupils practise pressure calculations in a practicalsituation.

Under pressure Pupils practise pressure calculations.

Approx. timing

20 min

40 min

20 min

Target group

C H E S

R/G G R S

✔ ✔

✔

Most pupils will ...

• use the relationship between force, area andpressure between solids

• identify everyday examples where high and lowpressure are useful.

Some pupils, making less progress will ...

• describe how force can be ‘spread out’ toreduce pressure or ‘focused’ to increasepressure

• identify some everyday examples where highand low pressure are useful.

Some pupils, making more progresswill ...

• use the definition of pressure incalculations to explain the operation of arange of devices.

Key wordspressure, exert, red only: newtons per square centimetre, pascal

Out-of-lesson learningHomework L1Textbook L1 end-of-spread questionsActivity L1b

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L2Lesson planning

guideTaking the plunge


Recap last lesson

Each group has a potato trimmedto give a flat base and nineidentical drawing pins. They try tobalance the potato on nine pinsand then on one pin, without thepins sticking in the potato.

Learning objectivesi Liquids cannot be squashed because there is no space between the particles.ii Pressure in a liquid acts equally and in all directions.iii A hydraulic machine uses a small force on a small input piston to produce a much larger force on a larger output piston connected to it.iv Water has its own pressure. The deeper you go, the heavier the weight of water so water pressure increases.

Scientific enquiryv Predict the behaviour of water under pressure. (Framework YTO Sc1 9f)

Learning outcomes

Share learning objectives

• Describe how pressure affectsliquids.

• Explain how hydraulic machineswork.

• Predict the behaviour of waterunder pressure. (Sc1)

Problem solving

Decide if each of a setof descriptions is of aliquid or a gas.

Brainstorming

Show pupils a balloonblown up with air. Askthem to imagine what willhappen as a diver holdsthe string and swims downto the ocean floor with it.

Capture interest

Show photos/videoclips of any hydraulicsystems.Catalyst InteractivePresentations 3


Review learning

Demonstrate a modelof a hydraulic system(e.g. syringe model, orpump model).

Sharing responses

Pupils work in groups to producetrue or false answers to questionsabout pressure in liquids as afollow-up to Activity L2a.

Group feedback

Each group summariseswhat they found out abouthydraulics in Activity L2band explains to the class.

Brainstorming

Pupils look at a diagram of thePeterborough Hydraulic Lift Lock inCanada and order a series ofstatements about how it works.

Looking ahead

Pupils use syringesto see whether aircan be compressed.


Textbook L2


Activity L2b Practical

Activity L2c Paper

Activity L2d Catalyst InteractivePresentations 3


i, ii, iii, ivand v

ii, iv and v

i, iii and v

ii, iii and v

i, ii and iii

Description


Pressure in liquids Demonstration to show pupils that the pressurein a liquid increases with depth and is equal in all directions, andbecause of this the surface of a liquid is always level.

Hydraulics Pupils use syringes to investigate the principles ofhydraulics. (The Help sheet is a demonstration.)

Squeezing liquids Pupils practise calculations involving hydraulicsystems.

Some animated pistons reinforce the idea that the small pistonmoves a long way and pushes the large piston out a short way. Alsoreinforces the idea that with the hydraulic system force can betransferred round corners.

Approx. timing

20 min

20 min

30 min

15 min

5–10 min

Target group

C H E S

R/G G R S

✔

✔ ✔ ✔

✔

✔

Most pupils will …

• use the relationship between force, area and pressure within liquids• apply the particle model of matter to explain why liquids are

incompressible• use the concept of transmission of pressure to predict resultant forces• identify some everyday effects of water pressure.

Some pupils, making less progress will …

• know that pressure acts equallyand in all directions in liquidsbecause the particles can’t besquashed.

Some pupils, making moreprogress will …

• use the definition of pressure incalculations to explain theoperation of a range of devices.

Key wordshydraulic machine, cylinder, piston, water pressure, red only: transmit,magnify

Out-of-lesson learningHomework L2Textbook L2 end-of-spread questionsActivity L2cWatch a hydraulic jack in operation – write a description of how it worksfor a catalogue

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L3Lesson planning

guidePressure in the air

Learning objectivesi Gases can be squashed because there is space between the particles.ii When a gas is squashed the volume goes down and the pressure goes up.iii When a squashed gas is released, the volume goes up and the pressure goes down. The fast expansion of released gases is used in aerosols and

pneumatic machines. (red only)iv Air has its own pressure. The higher up in the air you go, the lower the air pressure becomes, because the weight of air decreases.

Scientific enquiryv Describe how scientists showed that air has pressure. (Framework YTO Sc1 9a)


Recap last lesson

Pupils demonstrate the‘equal pressure’ and‘pressure at depth’equipment to the class.Measure water pressureat a depth.


• Describe how pressure affectsgases.

• Describe how gases are used inaerosols and machines.

• Describe some of theexperiments that scientists didto demonstrate that air haspressure. (Sc1)

Problem solving

Pupils consider what willhappen as a heliumballoon is released andgoes up through theatmosphere.

Capture interest (1)

Use a sink plunger to showthat once the suction pad isattached to something it isvery difficult to pull it off(because of air pressure).


Demonstrate the collapsingcan experiment (if not using in L3a).


Textbook L3



Activity L3cCatalyst InteractivePresentations 3


i, ii, iii, ivand v

iv and v

i, ii, iii and v

i, ii, iii andiv

Description


Air pressure Demonstrations to show pupils that air has a highpressure.

The pressure is on! Pupils do three short experiments to show thatair can be compressed, unlike water, and the pressure increases whenit is compressed. As an extension, pupils also look at gas cylinders.

Support animations of air pressing on things.

Approx. timing

20 min

30 min

25 min

10 min

Target group

C H E S

R/G G R S

✔

✔ ✔ (✔)

✔


Review learning

Look at pictures of a deep seadiver in a special pressure suitand an astronaut in a spacesuit. Compare and contrast theconditions.Catalyst InteractivePresentations 3

Sharing responses

Pupils look at the drinkbottle demonstration andin pairs explain it interms of air pressureusing what they havelearned from Activity L3a.

Group feedback

Pupils use evidencegathered from Activity L3bto answer questions aboutair pressure.

Word game

Check progress using acrossword about pressure.

Looking ahead

Show pupils a jar which youare having difficultyopening. Ask for suggestionshow to open it.

Learning outcomes


• apply the particle model of matter to explain whygases are compressible and the behaviour of gasesunder pressure

• describe the effects of gas under pressure in tyres• describe an effect of air pressure.


• know that when you squash a gas theparticles move closer together.

Some pupils, making more progress will …

• use the concept of pressure in gases toexplain the operation of a range of devicesand everyday experiences

• relate pressure in gases to density.

Key wordspneumatic machine, air pressure, red only: compressed

Out-of-lesson learningHomework L3Textbook L3 end-of-spread questions



L4Lesson planning

guideWhere’s the pivot?


Recap last lesson

Look at an aneroidbarometer. Link operation ofpointer into this lesson.Catalyst InteractivePresentations 3

Learning objectivesi A pivot is the point around which an object turns, such as a door or a crowbar.ii A lever is used to apply a force to make something turn around a pivot.iii The turning effect of a force depends on the size of the force and the distance along the lever (qualitative).

Scientific enquiryiv Understand how a long lever can improve precision of measurements. (Framework YTO Sc1 9d)

Learning outcomes


• Identify pivots, levers andturning effects.

• Recognise how longerpointers can improvemeasurement. (Sc1)

Problem solving

Consider what toolswould be best to undo arusty bolt.

Word game

Revise forces with aloop game.

Capture interest

Consider an animation of howengineers constructed theStonehenge trilithons. How didthey get such big stones upright?Catalyst Interactive Presentations 3


Review learning

Show video clips of opening bridgesand other large visual modernstructures, e.g. canal lock gates.Pupils identify pivot and lever.Catalyst Interactive Presentations 3

Sharing responses

Pupils look at picturesand identify pivotsand levers.

Group feedback

Pupils discuss what theydiscovered in a circus of experiments fromActivity L4a.

Word game

Pupils answer questionsfrom cards in pairs.

Looking ahead

Pupils consider whether wecan measure how good alever is.


Textbook L4


Activity L4b Paper

Activity L4c Catalyst InteractivePresentations 3


i, ii and iii

i, ii and iii

iii and iv

iii and iv

Description


Pivots and levers Pupils look at six examples of pivots and leversand think about the length of the lever and the distance it moves.

Pointer precision Pupils make a card meter which can be fitted witha long or short pointer, to see how this affects precision.

Support animation of a large and small pointer measuring something.

Approx. timing

20 min

25 min

15 min

5–10 min

Target group

C H E S

R/G G R S

✔

✔ (✔)

✔


• explain the action of levers, includingexamples in the human skeleton

• identify pivots and levers in everyday life• know that the further from the pivot a force

acts the less force is needed to move thelever.


• identify pivots and levers in everyday life• recognise that the turning effect of a force can

be increased by increasing the length of thelever arm and give a use of this.


• describe how the wheelbarrow acts as asimple machine

• be able to calculate moments.

Key wordspivot, lever, red only: turning effect

Out-of-lesson learningHomework L4Textbook L4 end-of-spread questionsMake list of devices in the home that use levers



L5Lesson planning

guideBalancing act

Learning objectivesi The turning effect of a force depends on the force applied and the distance from the force to the pivot. (green)ii The turning effect of a force is called the moment of a force. (red only)iii Moment of a force = force × distance. (red only)iv When the two moments/turning effects are unbalanced, a lever will turn.

Scientific enquiryv Describe how to balance objects on a beam. (Framework YTO Sc1 9f)

Learning outcomes


Textbook L5

Activity L5a Paper



i, ii, iii, ivand v

i, ii, iii, ivand v

i, ii, iii, ivand v

Description


Turning, turning Pupils answer questions that give further practicewith pivots, levers and turning effects.

Balance Pupils balance a mass on either side of a beam balance asan introduction to moments.

Approx. timing

20 min

20 min

15 min

Target group

C H E S

R/G G R S

✔

✔ (✔)

Key wordsturning effect, clockwise, anticlockwise, red only: moment

Out-of-lesson learningHomework L5Textbook L5 end-of-spread questionsActivity L5a


• use the relationship between force, area andpressure between solids and within liquidsand gases

• explain the action of levers, includingexamples in the human skeleton, in terms ofthe turning effect of a force

• use the principle of moments to explainbalance and give examples of its application,e.g. crane counterweight.


• recognise that the turning effect of a force canbe increased by increasing the length of thelever arm and give a use of this

• describe how to balance a seesaw.


• apply the principle of moments to explain arange of situations, including the action oflevers.


Recap last lesson

Ask a pupil to open thedoor, pushing near to andfar from the hinge.


• Explain the turning effectof a force.

• Use patterns to describehow to balance objects ona beam balance. (Sc1)

Problem solving

Set up a beam of wood onthe floor or some othersimulated ‘tightrope’.Pupils walk along it as ifit were a tightrope.

Brainstorming

Working in pairs,pupils count up thenumber of pivots inthe human skeleton.

Capture interest

Pupils look at a moveable model ofthe skeleton (if available). Move itto show different pivots.


Review learning

Show a balance with two scalepans and how it balances theturning effects of the weights andthe object.

Sharing responses

Pupils work in pairsusing whiteboards tosketch how theturning effect of aforce can be balanced.

Group feedback

Groups discuss what theydiscovered about turningeffects from Activity L5b.

Word game

Play hangman to recap key words.

Looking ahead

Show a couple of models ofcranes (maybe Lego) withand without acounterbalance.



L6Lesson planning

guideMoments in life

Learning objectivesi The turning effect of a force is called a moment (moment = force × distance) (green)ii Moments (red only – principle of moments) can be used to explain many everyday situations.iii A counterbalance is a weight that stops something falling over.iv The principle of moments says: in balance, the sum of the anticlockwise moments = the sum of the clockwise moments. (red only)

Scientific enquiryv Understand and be able to predict how objects will balance on a beam. (Framework YTO Sc1 9f)

Learning outcomes


Textbook L6

Activity L6a Paper

Activity L6b Paper


i, ii, iii, ivand v

i, ii, iii, ivand v

i, ii, iii, ivand v

Description


Stability Pupils investigate how stability of machines is linked topivots and levers.

More moment calculations Pupils are provided with extra practice incalculating moments.

Approx. timing

20 min

20 min

20 min

Target group

C H E S

R/G G R S

✔

✔ (✔)

Key wordsmoment, counterbalance, red only: principle of moments

Out-of-lesson learningHomework L6Textbook L6 end-of-spread questionsWatch a building site crane – write an advertisement for it


• use the principle of moments to explainbalance and give examples of its application,e.g. crane counterweight.


• recognise that the turning effect of a force(moments) can be used to explain balance.


• apply the principle of moments to explain arange of situations, including the action oflevers.


Recap last lesson

Set up a beam balance. Askfor suggestions as towhereabouts objects shouldbe put to balance eachother.


• Use the idea of momentsto explain everydaysituations.

Problem solving

Using an animal shape(e.g. a duck), how canyou suspend it so itwon’t go tail or beakdown?


Show some toys thatbalance well. Discuss howthey work in terms ofmoments.


Look at some symmetricalobjects like a fork, a pair ofscissors or a garden spade andsee where you can balance themon your finger.


Review learning

Pupils look at a video clip of acrane lifting a load, acounterbalanced canal swing bridgeopening, and a level crossingbarrier opening.Catalyst Interactive Presentations 3

Sharing responses

Challenge pupils tostand straight with sideof foot and shouldertouching the wall, thenlift the other foot offthe ground withoutfalling over.

Group feedback

Pupils complete theStarter activity usingtheir findings tosuspend the duckwithout it tipping beakdown or tail down.

Word game

Check progress using acrossword.

Looking back

Pupils revise andconsolidate knowledge fromthe unit.


Tasha Goddard

Underline


L7Lesson planning

guideGetting balanced – Think aboutequilibrium

Learning objectivesi The concept of equilibrium using the balance beam.ii Balancing the beam with one set of weights on either side. (green)iii Other ways of balancing the beam – two sets of weights on each side of the beam in different holes. (red only)iv Applying the concept of equilibrium: a seesaw and hydraulic equilibrium. (red only)

The structure of this lesson is based around the CASE approach. The starter activities give concrete preparation. The main activities move away from theconcrete towards a challenging situation, where pupils need to think. The extended plenary gives pupils time to discuss what they have learnt, tonegotiate a method to commit to paper and express their ideas verbally to the rest of the class.

Scientific enquiryv Describe how the pattern of results of balancing the beam support the principle of moments (Framework YTO Sc1 9f)

Learning outcomes


Textbook L7



i, ii and v

i and v

Description


Getting balanced Pupils investigate equilibrium and ascertain thatthe clockwise moments are equal to the anticlockwise moments.

Approx. timing

30 min

40 min

Target group

C H E S

R/G G R S

✔ ✔ ✔

Key wordsequilibrium

Out-of-lesson learningTextbook L7 end-of-spread questions


• apply the concept of equilibrium to thebalance beam

• reflect upon the idea of a combination of fourvariables contributing to equilibrium

• analyse a problem in terms of equilibrium.


• identify the four variables that affect whethera beam will balance

• begin to understand the idea of equilibrium• with help, analyse a problem in terms of

equilibrium.


• resolve cognitive conflict arising from usingtwo sets of weights in different holes on eachside of a beam balance

• apply the concept of equilibrium to a simplehydraulic system.


Bridging to the unit

On a seesaw a heavy childcan be balanced by a lightchild. Is there a rule thattells you where each childshould sit?

Setting the context

Demonstrate clockwise andanticlockwise moments witha beam balance.

Concrete preparation (1)

Demonstrate a commercial beambalance (if available or look at pictureon CD).Catalyst Interactive Presentations 3


Work out the mass of the heavy ‘weights’ in aclock using a beam and a 1kg bag of sugar.Catalyst Interactive Presentations 3


Group feedback

Pupils discuss their results in groups and write a sentence to explain howweights on either side of a pivot can be balanced by adjusting the distancefrom the pivot.

Bridging to other topics

Extend the idea of equilibrium and balance to other topics whichpupils may have already met or may meet in the future.


L Unit mapPressure and moments


Copy the unit map and use these words to help you complete it.You may add words of your own too.

airair pressureanticlockwiseareabalancedbarometerbeam balanceclockwisecompression Rcounterbalancecylinderdistanceequilibriumexertforce

hydraulicsjointslevernewtons per square

metre Rparticlespascals Rpistonpivotpneumaticsprinciple of moments Runbalancedvolumewaterwater pressure

Pressure andmoments

Pressure

Pressurein solids

Pressurein liquids

Pressurein gases

Moments

Pivots and levers

Turning effectsand moments

Unitmaps.qxd 18-Jun-04 11:36 AM Page 12


L1 StartersUnder pressure

Introduce the unit� Either draw the outline of the unit map on the board then ask pupils to give

you words to add, saying where to add them. Suggest some words yourselfwhen necessary to keep pupils on the right track.

� Or give out the unit map and ask pupils to work in groups deciding how toadd the listed words to the diagram. Then go through it on the board as eachgroup gives suggestions.

Share learning objectives� Write the learning objectives on board and show why it is important that we

know about these ideas.� Ask pupils what they think pressure means.� Explain that pressure has a scientific meaning and it can be measured. Link

their understanding of the word to the scientific meaning.� Introduce force and area. Discuss how the same person will sink into soft

ground a different amount depending on footwear, e.g. stiletto heels orsnowshoes. The force (weight) is the same, but the pressure has changedbecause the area has changed.

Problem solving� Pupils work in pairs or groups. They look at the pupil sheet and plan how to

rescue the child who has fallen through the ice.� The rescuer is larger than the child, so must use some method of lowering the

pressure.

Word game� Play a game of hangman to remind pupils of prior knowledge about forces.

Use words such as: weight, upthrust, newton, forcemeter, reaction.

Capture interestSafety note: If any student has a severe nut allergy (i.e. possible anaphylacticshock) it will not be possible to do this with the student in the same room.Students with a mild nut allergy may remain but should not take part. To avoidthis problem you may be able to use dry pasta ‘shapes’ or even some hard sweetsbut try beforehand to see what works.

� You will need a bag of walnuts in their shells. Give some pupils two of thewalnuts and ask if they can crack them in their hands without using any tools.

� After a short time trying, show that it can be done if you hold two walnuts inone hand and squeeze them together. They have a small area of contact sothe pressure exerted at this point is much higher than anywhere else and theweaker nut will crack.

� If pupils’ hands, or your hands, are too small, then the nuts can be crackedby holding them between the palms of both hands. Close both handsaround them and squeeze. Have some spare walnuts, as some are harder tocrack than others.

➔ Unit map

➔ Pupil sheet

Equipmentwalnuts in shells


Introduce the unit

Unit map for Pressureand moments.


• Define what pressure is.• Describe how the force and the

area over which it acts changethe pressure.

Problem solving

Show pupils the scenario of achild falling through the ice.Pupils discuss how a largeadult can rescue the child.

Word game

Play a game ofhangman to remindpupils of forcesknowledge from Year 7.

Capture interest

Give some pupils two walnutseach and ask if they cancrack them with their hands.

L-Starters.qxd 17-May-04 6:18 PM Page 1

L1 StartersUnder pressure

Problem solving

What should the teenagers do to help the child?

Plan a rescue.

Every second counts.




L2 StartersTaking the plunge

Recap last lesson� Pupils put the nine drawing pins close together, points up, and

balance the potato carefully on top. Challenge them to do this sogently that when it is picked up, no pins come too. Blunter pins workbest. The pressure is not high enough for the pins to stick in thepotato.

� Now they try with just one of the pins. They hold the potato over thepin so the pin is in the middle of the flat area. As they put the potatoon the pin and gently let go, the potato will settle with part of ittouching the table. This should not matter – the pressure will havebeen high enough to stick the pin into the potato.

� Ask pupils to explain this. They have changed the contact area. Withone pin the contact area is reduced to 1/9, so pressure is nine timeshigher.

Share learning objectives� Write the learning objectives on board and show why it is important

that we know about these ideas.

� Ask pupils what they think pressure in liquids means, or what they knowabout pressure in liquids. Focus on particles in liquids from Unit 7G.

� Pupils should have had experience of swimming under water, andfeeling pressure in their ears.

Problem solving� Pupils read the descriptions on the pupil sheet and decide if each one

is of a liquid or a gas, or if it could apply to both. They identify theodd one out, which is neither liquid nor gas.

Brainstorming� Show pupils an inflated balloon. Ask them to imagine what will

happen when it is thrown into the ocean and a diver takes hold of thestring and swims down to the ocean floor with it.

Capture interest� Pupils watch the video showing the operation of a hydraulic

controlled dinosaur/monster/animal. The fluid in the pipes transmitsthe pressure to the piston which moves the model.

� Tell pupils that they are going to find out how the hydraulic systemworks.

Equipmentfor each group: nine identicaldrawing pins (type withfairly blunt tips); one potatotrimmed to have a flat base

➔ Pupil sheet

Answers1 both; 2 liquid; 3 gas; 4 liquid; 5 gas; 6 gas; 7 liquid; 8 both; 9 neither(odd one out); 10 both

➔ Teacher sheet

➔ Catalyst InteractivePresentations 3


Recap last lesson

Each group has a potato trimmedto give a flat base and nineidentical drawing pins. They try tobalance the potato on nine pinsand then on one pin, without thepins sticking in the potato.


• Describe how pressureaffects liquids.

• Explain how hydraulicmachines work.

• Predict the behaviour ofwater under pressure. (Sc1)

Problem solving

Decide if each of a setof descriptions is of aliquid or a gas.

Brainstorming

Show pupils a balloonblown up with air. Askthem to imagine what willhappen as a diver holds thestring and swims down tothe ocean floor with it.

Capture interest

Show photos/video clipsof any hydraulic systems.Catalyst InteractivePresentations 3


Sheet 1 of 1

StartersL2 Taking the plunge

Problem solving

Decide whether each of sentences describes a liquid or a gas orboth a liquid and a gas.

One statement is not true for liquids or gases. Which one?

1 It is made up of particles.2 The particles are touching.3 The particles spread out from each other to fill the container.4 It stays the same size, but changes shape.5 It changes size and shape.6 It is easy to squash (compress).7 It is difficult to squash (compress).8 When it is heated the particles move faster.9 The particles expand (get bigger) when heated.10 The particles spread out and rise upwards when heated.

© Harcourt Education Ltd 2004 Catalyst 3This worksheet may have been altered from the original on the CD-ROM.


Problem solving

Decide whether each of sentences describes a liquid or a gas orboth a liquid and a gas.

One statement is not true for liquids or gases. Which one?

1 It is made up of particles.2 The particles are touching.3 The particles spread out from each other to fill the container.4 It stays the same size, but changes shape.5 It changes size and shape.6 It is easy to squash (compress).7 It is difficult to squash (compress).8 When it is heated the particles move faster.9 The particles expand (get bigger) when heated.10 The particles spread out and rise upwards when heated.





BrainstormingTeacher sheetEquipmentinflated balloon

Pupils imagine what will happen when an inflated balloon is thrown into theocean and a diver takes hold of the string and swims down to the ocean floorwith it.

They should divide a white board into four and draw four diagrams showingthe balloon, the string, and the diver’s hand (a circle would do): a before the diver swims down; b just below the surface; c further down; d as far down as the diver can go.

Answersa Balloon floats on surface of water, string is slack.

b Balloon just below surface, maybe slightly smaller (point out that it shouldbe slightly squashed, but this would be quite a small change which mightnot be noticeable), string should be taut and vertical as balloon tries to rise.

c Balloon now visibly smaller, string still taut.

d Balloon very small, just as when you start to inflate it, and rubber is notstretched, string still taut.



L3 StartersPressure in the air

Recap last lesson� Set up the equipment you used for Activity L2a: the

pressure in all directions and pressure at a depthdemonstrations. Ask for volunteers to pour the water intoeach of the demonstrations and to tell the class what ishappening and what it shows.

� Ask other pupils if the demonstrator has remembered allthe points.

� If available, use a pressure meter to measure pressure atdifferent depths in water.

Share learning objectives� Write the learning objectives on board and show why it is

important that we know about these ideas.

� Air is all around us, many things work the way they dobecause of air pressure.

� We make use of pressure in gases when we use aerosols, gascylinders, and machines that work using compressed air.

Problem solving� Pupils consider what will happen as a helium balloon is

released and goes up through the atmosphere. They candraw pictures on a white board: a at ground level; b at rooftop level; c at cloud level; d as high as it can go.

� Encourage pupils to think about what will happen to thepressure outside the balloon as the balloon goes up. (It willhelp them to think about a balloon coming up from thebottom of the sea.)

Capture interest (1)� Use a sink plunger to show that a suction pad works

because of air pressure.

Capture interest (2)� Pupils watch the collapsing can experiment. There are two

ways of showing the effect of removing air from the can.

Equipment‘pressure at depth’ and ‘equal pressure’demonstrations (see Activity L2a)

Equipmenthelium balloon if available

Answersa Balloon goes up because helium is

lighter than air.b, c Balloon becomes larger as it goes

higher. At higher altitudes the airpressure outside the balloon is less,so the pressure inside needs to fallso that the pressures remain equal.Pressure is less when the helium gasoccupies a larger volume – so theballoon gets bigger.

d As the balloon gets bigger it willeventually burst.

➔ Teacher sheet

➔ Teacher sheet


Recap last lesson

Pupils demonstrate the‘equal pressure’ and‘pressure at depth’equipment to the class.Measure water pressure ata depth.


• Describe how pressure affects gases.• Describe how gases are used in

aerosols and machines. • Describe some of the experiments

that scientists did to demonstratethat air has pressure. (Sc1)

Problem solving

Pupils consider whatwill happen as a heliumballoon is released andgoes up through theatmosphere.


Use a sink plunger to showthat once the suction padis attached to something itis very difficult to pull itoff (because of airpressure).


Demonstrate thecollapsing can experiment(if not using in L3a).



L3 StartersPressure in the air

Teacher sheet

Capture interest (1)Equipmentsink plunger; method of attaching weights; weights

� Attach a sink plunger to a smooth surface (try in advance to find suitablesurfaces). Pressing on the suction pad pushes the air out so that there is littleair left between the suction pad and the surface. Air pressure forces thesuction pad onto the table/cupboard, etc.

� Show that once the suction pad is attached to something it is very difficultto pull it off (because of air pressure). For the pad to come off it would haveto move away from the surface, but as the handle is pulled the size of thespace between the surface and the suction pad gets larger and so the airpressure becomes less. The air pressure outside is larger than the pressureinside, acting to keep the pad on the surface.

� If it can be attached so it is hanging downwards, e.g. from a cupboard,weights can be attached to show that air pressure on an area can give alarge force. Show that it is important to have a good seal otherwise air willget in and equalise the pressure so that the suction pad is no longer held inplace.

Capture interest (2)Equipmentrotary pump or Bunsen burner and dry cloth for handling hot can; tin can withscrew lid (can be supplied for experiment by Philip Harris)

� Method 1: Place the can on a tripod over a Bunsen and boil a small amountof water in the can. When steam is coming out of the top, remove the canfrom the heat and screw the lid on tightly. Leave to cool, or cool under acold tap. As the steam condenses, a partial vacuum is created in the can.The air pressure outside crushes the can. (It is important to realise it is thesquashing force from outside, not a sucking force inside the can.)

� Method 2: Attach the can to a rotary pump and pump out the air.



L4 StartersWhere’s the pivot?

Recap last lesson� Pupils look at an aneroid barometer. Use an example if available. Ask

questions of the class as you talk about it.� What does it measure? They may know that air pressure changes with

the weather: High = settled, calm, clear. Low = windy, stormy.� What would happen if you took it up a mountain? Pressure would fall.� How does it work? Show them the ‘tin’, which is sealed and will be

squashed in more as pressure increases, and expand out again aspressure decreases.

� The movement is very small, and must be magnified by levers so thatthe pointer moves enough to read. This leads in to Activity L4b.

Share learning objectives� Write the learning objectives on board and show why it is important

that we know about these ideas:� Our body contains levers, and our joints are pivots, this is how we

move. It is important to understand how we do this and how we candevelop tools to do jobs making use of levers and pivots.

� Levers magnify an effect, so if we want to measure something it will beeasy to measure if we use levers to make the effect larger. This will makethe measurement more precise.

Problem solving� Pupils think about the problem of a rusty bolt that can’t be undone with

a spanner.� Show the bolt. Explain that you have tried putting oil on it, and heating

it. If necessary, show some spanners with different length handles and ahammer to prompt them. Some may know instinctively that a longerspanner is needed but will not be able to explain why.

Word game� Give each pupil a card containing a question and an answer. Ask one pupil

to stand up and read out just the question on their card, then sit down. Thepupil who has an appropriate answer to this question stands up, reads outtheir answer, then asks the question on their card and sits down, and so on.

� The game is complete when the pupil who started the game stands up fora second time to read out the answer on their card. The loop is complete.

� If there are not enough question/answer cards for the whole class, youmay need to make extra copies. Some pupils will have the samequestion/answer card – the first one to stand up gets to read their answerand ask their question.

Capture interest� Show photos of large standing stones, such as at Stonehenge, and ask

pupils to consider how people managed to get them upright.� Watch video clip or animation of stones being levered upright.


Equipmenta rusty bolt to be undone; ahammer; several spannersthat fit the bolt but havedifferent length handlesand/or a hollow metal tubewhich fits over a spanner tomake the handle longer (a hollow metal tube is aconvenient way to extendthe length of the spannerprovided for changing a carwheel, where the nuts areoften difficult to undo)

➔ Pupil sheet



Recap last lesson

Look at an aneroidbarometer. Link operationof pointer into this lesson.Catalyst InteractivePresentations 3


• Identify pivots, levers andturning effects.

• Recognise how longerpointers can improvemeasurement. (Sc1)

Problem solving

Consider what toolswould be best to undoa rusty bolt.

Word game

Revise forces with aloop game.

Capture interest

Pupils consider an animation of howengineers constructed theStonehenge trilithons. How did theyget such big stones upright? Catalyst Interactive Presentations 3


L4 StartersWhere’s the pivot?

Word game


Q

What do we call theforce on you which is caused by gravity?

Q

What is the force thattries to stop thingsmoving?

Q

What units are used formeasuring force?

Q

If something is notmoving what can yousay about the forces onit?

Q

How does gravity on theMoon compare togravity on the Earth?

Q

What force makes woodfloat?

Q

Pressure is force dividedby … (what?)

Q

What is the force thatslows objects travelling is through air?

Q

What force stops youfalling through theground?

Q

What is used to measureforce?

A

magnetism

A

friction

A

The forces arebalanced.

A

upthrust

A

A forcemeter.

Q

What is the force thatcan attract or repelbetween two pieces ofiron or steel?

A

Speed thingsup.

Q

A force can slow thingsdown or changedirection. What else canit do?

A

The reactionforce.

A

Air resistance.

A

newtons

A

weight

A

area

A

Gravity on theMoon less thangravity on theEarth.



L5 StartersBalancing act

Recap last lesson� A pupil demonstrates opening a door. Ask other pupils to identify the

pivot and the lever.� Measure the force required to open the door by pulling it open using a

forcemeter attached to the handle (try in advance).� Consider if it is easier or harder to open/close the door by pushing

closer to the hinge.� If two people push, one on each side, so that the door does not move,

which pair would have to push harder, the one nearer the hinge or theone near the handle?

Share learning objectives� Write the learning objectives on the board and show why it is

important that we know about these ideas.� When we open doors, use spanners, and undo jars we are using a force in

a special way to get a turning effect. These are useful to us. We need tounderstand these turning effects so we can make them bigger or smaller.

� On a seesaw we can balance by trial and error, but when engineersdesign bridges and other structures we want to know that things arebalanced. We need to know how to make sure a beam will be balanced.

Problem solving� Pupils attempt to walk along a simulated tightrope without falling off.� Ask pupils to notice how they balance. You instinctively move parts of

the body to keep the clockwise turning effects equal to theanticlockwise turning effects. Sticking an arm further from the ropeincreases its turning effect – mass stays the same but the distanceincreases.

� Ask pupils where the pivot is. It is at the feet.

Brainstorming� Pupils work in pairs to count up the number of pivots in the human

skeleton.� Encourage them to use their own arms and legs to help with

counting.

Capture interest� Look at the skeleton, especially the pivot at the elbow and knee.� Demonstrate how the joints move and the range of movement

available.� Consider the difference between holding a weight with the arm

horizontal (lever effect) and the arm vertical.

Equipmenta forcemeter that can beattached to door handle andwhich measures force in the range required to openthe door

Equipmenta simulated tightrope, e.g. a 5 cm × 5 cm × 2 m piece ofwood

Safety note: Do not attemptto use an actual rope at anyheight. A 2–3m length ofwood with an approximatecross section of 50–60 mmeach side laid flat on the floorwill do.Answereach hand and foot has 15;each arm and leg has 3; +waist + neck + jaw = 60 + 12 +3 = 75


Recap last lesson

Ask a pupil to open thedoor, pushing near to andfar from the hinge.

Share learningobjectives

• Explain the turning effectof a force.

• Use patterns to describehow to balance objects ona beam balance. (Sc1)

Problem solving

Set up a beam of wood onthe floor or some othersimulated ‘tightrope’. Pupilswalk along it as if it were atightrope.

Brainstorming

Working in pairs, pupilscount up the number ofpivots in the humanskeleton.

Capture interest

Pupils look at a moveablemodel of the skeleton (ifavailable). Move it to showdifferent pivots.



L6 StartersMoments in life

Recap last lesson� Set up a large beam balance. Select some unusual pairs of objects, e.g. two

different shoes, and ask where they should be put to balance each other.

� Choose unusual objects, e.g. a balloon of air and an empty balloon, and ask ifthey will balance at the same distances from the pivot. Show that a largefeather can balance a piece of lead if the distances are chosen correctly. (Apartfrom items chosen by pupils, weigh other items in advance and have a noteof the masses, so that you know if it is possible to balance them, and canspeed up the trial and error process.)

Share learning objectives� Write the learning objectives on board and show why it is important that we

know about these ideas.

� When we design, make, or just use objects, it is important to know whichobjects will balance safely (vases, cranes, gymnasts, bridges and buildings).We need to understand how things balance.

� Sometimes we can predict if things will balance from our understanding, butsometimes we need to calculate values exactly.

Problem solving� Pupils discover how to suspend a duck shape so it won’t go tail or beak down.

Capture interest (1)� Show some toys that balance in unusual ways.

� Discuss why things balance. Each toy is made up of weights all at differentdistances from the pivot. All of these must be in balance.

Capture interest (2)� Take any objects and try balancing them on a finger or on the edge of a ruler

(supported on its edge). Demonstrate heavier objects. Pupils can try pencils,rulers and pencil cases and spoons or spatulas and forks if available forthemselves.

� Pupils discuss how they attempt to balance the object, e.g. if they can seethat one side is heavier than the other they try a pivot point closer to theheavy end. This reduces the moment of the heavier weight, and increases themoment of the lighter weight.

Equipmentbeam balance;hangers; items to testincluding: twoidentical balloons, oneinflated with air, onenot, on identicalthread; a large featherand a small leadweight; an air balloonand a helium balloon;a piece of lead with amass of perhaps 10 g

➔ Teacher sheet

➔ Pupil sheet

➔ Teacher sheet

Equipmenttoys that balance (seeTeacher sheet); potato;two forks; glass; 2pcoin; Blu-Tack

Equipmentfork; scissors; gardenspade; otherunbreakable objects,preferably symmetricalas pupils can ignoreone dimension andsee what is happeningmore easily


Recap last lesson

Set up a beam balance. Askfor suggestions as towhereabouts objects shouldbe put to balance each other.


• Use the idea of moments toexplain everyday situations.

Problem solving

Using an animal shape(e.g. a duck), how canyou suspend it so it won’tgo tail or beak down?


Show some toys thatbalance well. Discuss howthey work in terms ofmoments.


Look at some symmetricalobjects like a fork, a pair ofscissors or garden spade andsee where you can balancethem on your finger.



Problem solvingTeacher sheetEquipmentscissors; rulers and some way of supporting rulers standing ontheir edge (e.g. Blu-Tack or mirror stands); string for suspendingthe animal; two ducks already cut out with holes and string,one that goes beak down and one that goes tail down

� Pupils work in pairs or groups. They cut the animal out ofthe piece of card. This could be the duck provided, oranother animal shape.

� They consider how they could find out where to fix a stringso that it doesn’t hang with its beak pointing down or its tailpointing down.

� This activity could be completed now, see below, or as aplenary; see ‘Group feedback’.

� If you are completing as a plenary then demonstrate whathappens if you put the hole in the wrong place – the duckhangs beak down or tail down. Finish by saying that by theend of the lesson they should know how to get the hole inthe right place.

� If you are completing the activity now then demonstratehow, with the ruler standing on its edge (supported by Blu-Tack), pupils can carefully balance the card on the edgeof the ruler so that the ruler makes a line they want to bevertical when the duck is hanging up. Pupils mark theposition of the ruler on the duck; the hole for the string willneed to be on this line. They make a hole at the top of theline and attach the string. The duck should hang withouttipping up or down.


4

Blu-Tack

Pupils mark rulerline on duck

card duck

ruler



Problem solving

Sheet 1 of 1

Sheet 1 of 1


StartersL6 Moments in life


Problem solving



Capture interest (1)Teacher sheet


weight

pivot point

C

weight

pivot point

weighted base, so centre ofmass C is close to the base

C

balance here

Blu-Tack Blu-Tack

2p

potato

fork

glassBlu-Tack

This bird can be enlarged and cutout of card. With a small piece ofBlu-Tack stuck to the underside of each wing it will balance on thepoint of a pen or finger placed onits beak.

The diagram shows an aerialview. Push the 2p coin into thepotato so that it is half-way in.By adjusting the amount andposition of the Blu-Tack thepotato can be made to balancewith the 2p coin on the edge ofthe glass. With heavy forks theBlu-Tack may not be necessary.

Any wobbly toy whichworks like the wobbly man can be used.



L7 StartersGetting balanced – Think about

Bridging to the unit� Demonstrate that on a seesaw a heavy child can be

balanced by a light child. Ask if this can only be doneby trial and error. Could pupils find a rule that tellsthem where the second child should sit? If so, thiswould be useful when balancing things and, forexample, in the design of measuring scales.

Setting the context� Demonstrate a beam with no masses on it which is

balanced. (Balance it with Blu-Tack if necessary.)

� Ask different pupils to demonstrate a clockwise momentand an anticlockwise moment, by pushing the beam.There are four possibilities – up and down on each side.

Concrete preparation (1)� Demonstrate a commercial beam balance (the type with

one scale pan and masses that slide along a beam untilit balances; then the mass is read off from the scale).

� Discuss the principle with pupils. The mass is notchanging but the distance of the mass from the pivotchanges. Ask pupils if there is a rule that can be used towork out mass from position.

Concrete preparation (2)Tell pupils this story:

� A clock needs repairing. It has very heavy ‘weights’(hard to lift) and the thread they were hung on hasbroken.

� There is a choice of cheap thread that will take 5 kg orexpensive thread that will take 10 kg. You need to knowthe masses of the clock ‘weights’, but there are no scales.Hint: use a 1 kg bag of sugar.

� After discussion, show that the 1 kg bag can balance thelarge mass on a beam balance. Measure the twodistances from the pivot.

� The lesson will show how the distances can be used towork out the mass.

Safety note: Do not let pupils lift the large mass, andmake sure it can’t fall – do the experiment at floor level.

Equipmentmodel ‘seesaw’ with a ‘light’ and ‘heavy’‘child’ (could be a beam balance with twodifferent masses)

Equipmentbeam balance; Blu-Tack

➔ Catalyst Interactive Presentations 3

Equipmentplank or beam of wood; pivot; 1 kg bag ofsugar; large mass (several kg); ruler



Bridging to the unit

On a seesaw a heavy child canbe balanced by a light child. Isthere a rule that tells you whereeach child should sit?

Setting the context

Demonstrate clockwise andanticlockwise moments with abeam balance.


Demonstrate a commercial beambalance (if available or look atpicture on CD). Catalyst Interactive Presentations 3


Work out the mass of the heavy‘weights’ in a clock using a beam anda 1 kg bag of sugar. Catalyst Interactive Presentations 3


L1aTeacher

activity notesFoot pressure

Running the activityCore: Pupils are asked to predict if the pressure they put on the floor will be more if they stand on one footor on two feet. The pupils measure the area of their shoes (you could ask them to bring stilettos, trainers, orother different examples, or provide some for the lesson) by drawing around their shoes with a pencil onsquared paper (1 cm2). They then calculate their force (weight) by using newton scales. From these figuresthey can calculate the pressure they are putting on the floor.Help: Pupils are asked to predict if the pressure they put on the floor will be more if they stand on one footor on two feet. The pupils measure the area of their shoes by drawing around their shoes with a pencil onsquared paper (1 cm2) (flat soles such as trainers would be easiest). They are told to count the number ofwhole squares. They then calculate their force (weight) by using newton scales. From these figures they cancalculate the pressure they are putting on the floor.

Other relevant materialsSkill sheet 7: Good results

Expected outcomesCore: Pupils complete the practical and worksheet. This give them practice in calculating pressure in aproblem that relates directly to them. They see that increasing area decreases pressure.Help: Pupils complete the practical and worksheet. They calculate pressure to complete the experiment, butthe focus is on the idea that increasing area decreases pressure, in a problem that relates directly to them.

PitfallsCalculating how many squares have been covered is often difficult. The easiest but least accurate method isto count all the whole squares. For a more accurate count include all those over half size. It helps to put amark in each square as it is counted. Shoes are easier than bare feet, because pupils can remove them todraw round, and force is spread over the whole sole, whereas not all your foot touches the ground (think ofwet footprints). Although shoes with heels have a middle section not touching the floor, this can usuallybe marked out afterwards by joining points on either side of the shoe, or by noticing the dusty footprint.

ICT opportunitiesIt would be possible to set up a spreadsheet for the results and subsequent calculations of pressure. Thiswould enable pupils to graph them to look at the relationship between area and pressure or between forceand pressure.

AnswersCore:

1 Pupil’s prediction, e.g. pressure will be higher when you stand on one foot than on two. 2 On two feetthe pressure is less. 3 a Pressure increases. b Pressure decreases. 4 No problems expected, but depends onpupil’s own experiment. 5 Possible problems: whether to count part square; drawing around the heel andfront part of shoe. 6 Depends on pupil’s own experiment.

Help:

1 Pupil’s prediction: more, the same or less. 2 a Right/wrong (depends on prediction) more, the same,less. b increase c decrease 3 – 4 See Core Questions 4–5. 5 – 6 Depends on pupil’s own experiment.


Type Purpose DifferentiationPractical Pupils practise pressure calculations in a practical situation. Core, Help

L-Teachers.qxd 17-May-04 7:43 PM Page 1

L1aTechnician

activity notesFoot pressure

EquipmentFor each group:

� squared paper (1 cm squares)� newton scales

For your informationRunning the activityCore: Pupils are asked to predict if the pressure they put on the floor will be more if theystand on one foot or on two feet. The pupils measure the area of their shoes (you could askthem to bring stilettos, trainers, or other different examples, or provide some for the lesson)by drawing around their shoes with a pencil on squared paper (1 cm2). They then calculatetheir force (weight) by using newton scales. From these figures they can calculate thepressure they are putting on the floor.

Help: Pupils are asked to predict if the pressure they put on the floor will be more if theystand on one foot or on two feet. The pupils measure the area of their shoes by drawingaround their shoes with a pencil on squared paper (1 cm2) (flat soles such as trainers wouldbe easiest). They are told to count the number of whole squares. They then calculate theirforce (weight) by using newton scales. From these figures they can calculate the pressure theyare putting on the floor.

Expected outcomesCore: Pupils complete the practical and worksheet. This give them practice in calculatingpressure in a problem that relates directly to them. They see that increasing area decreasespressure.

Help: Pupils complete the practical and worksheet. They calculate pressure to complete theexperiment, but the focus is on the idea that increasing area decreases pressure, in a problemthat relates directly to them.

PitfallsCalculating how many squares have been covered is often difficult. The easiest but leastaccurate method is to count all the whole squares. For a more accurate count include allthose over half size. It helps to put a mark in each square as it is counted. Shoes are easierthan bare feet, because pupils can remove them to draw round, and force is spread over thewhole sole, whereas not all your foot touches the ground (think of wet footprints). Althoughshoes with heels have a middle section not touching the floor, this can usually be markedout afterwards by joining points on either side of the shoe, or by noticing the dustyfootprint.

ICT opportunitiesIt would be possible to set up a spreadsheet available on the CD-ROM for the results andsubsequent calculations of pressure. This would enable pupils to graph them to look at therelationship between area and pressure or between force and pressure.


Type Description DifferentiationPractical Pupils practise pressure calculations in a practical situation. Core, Help

L-Technician.qxd 18-May-04 12:37 PM Page 1

L1Activity

Core

Pressure is a measure of how much force there is for a givenarea. By standing on the ground we are putting pressure onthe ground beneath our feet. You are going to find out howmuch pressure you exert through your feet.

Predicting

The force pulling downwards on you is your weight. The area thatthe force is spread over is the area of your feet.

1 Make a prediction about the pressure you exert on the ground:will the pressure be higher when you stand on one foot or ontwo, or will it stay the same?

Obtaining evidence

1 Make a table like the one below to record the measurements.


L1a Foot pressure

Foot Area of shoes Force on area Pressure in square (weight) in (weight ÷ area) centimetres newtons (N) in newtons per square (cm2) centimetre (N/cm2)

left

right

both

2 Draw around both your shoes, one at a time, using a penciland squared paper (each square is 1 cm2).

3 Count the number of full squares that are covered by your shoes. This will give you the approximate measurement of the area of your shoes in cm2. Calculate the total area of both shoes.

4 Use newton scales to measure your weight and write it in thetable.

L-Activities.qxd 17-May-04 7:07 PM Page 1

L1aActivity

CoreFoot pressure (continued)

Presenting the results

5 Complete the table of results by calculating the pressure usingthe equation:

pressure =force in N

area in cm2

Considering the evidence

2 Was your prediction correct? Was there a difference in pressurebetween standing on one foot and on two feet, and did thepressure increase or decrease?

3 Explain what would happen to the pressure beneath your feet if:

a your weight increasedb the area of your shoes increased.

Evaluating

4 Were there difficulties in measuring weight?5 Were there difficulties in measuring shoe area?6 Explain how you made your measurements accurate and what

improvements you would make if you were repeating theexperiment.



L1aActivity

HelpFoot pressure

Pressure is a measure of how much force there is for a givenarea. By standing on the ground we are putting pressure onthe ground beneath our feet. You are going to find out howmuch pressure you exert through your feet.

Predicting

1 Copy and complete this prediction, choosing from the wordsbelow.

I predict that I will put pressure on theground when I am standing on one foot than when I amstanding on two feet.

Obtaining evidence

1 Make a table like the one below to record the measurements.


Foot Area of shoes Force on area Pressure in square (weight) in (weight ÷ area) centimetres newtons (N) in newtons per square (cm2) centimetre (N/cm2)

left

right

both

2 Draw around both your shoes, one at a time, using a penciland squared paper (each square is 1 cm2).

3 Count the number of full squares that are covered by yourshoes. (Tip: put a dot in each square as you count it so youwill know which you have counted.) This will give you theapproximate measurement of the area of each of your shoes in cm2. Calculate the total area of both shoes.

4 Use newton scales to measure your weight and write it in the table.

the same more less


L1aActivity

HelpFoot pressure (continued)


5 Use a calculator to work out the pressure for each shoe and forboth shoes:

pressure =force in N

area in cm2

Divide the weight by the area of the shoes and write theanswer (the pressure) in the table.


2 Complete these sentences by choosing from the words inbold.

a My prediction was right/wrong. When I stand on onefoot the pressure on the ground is the same/more/lessthan when I stand on two feet because my weight is thesame/more/less but the area I am standing on is thesame/more/less.

b If my weight increases the pressure beneath my feet willincrease/decrease/stay the same.

c If the area of my shoes increases the pressure beneath myfeet will increase/decrease/stay the same.

Evaluating

3 Did you have a problem measuring weight with the newton

scales? If yes, what was the problem?

4 Did you have any problems measuring shoe area using the

squared paper and counting squares? If yes, what were they?

5 Write down one thing that you did to make your

measurements more accurate.

6 Write down one thing you would do next time to improve

your experiment.



L1bTeacher

activity notesUnder pressure

Running the activityPupils answer the questions, showing all working out. The activity should take 20minutes to complete.

Other relevant materialsSkill sheet 37: Calculations

Skill sheet 38: Converting units

Answers1 A = 2, B = 6, C = 20, D = 4000, E = 2, F = 10, G = 0.004

2 a The area of the ends of the stilts is much smaller than the area of the clown’s feet,so the pressure from the stilts is greater and they sink into the sand

b Lose weight/put wider ends on the stilts (this is the most practical).c 2800 N/m2

3 a 0.05 m2

b 14 000 N/m2

4 a 12 000 Pab 14 000 Pa


Type Purpose DifferentiationPaper Pupils practise pressure calculations. Extension

L-Teachers.qxd 21-Jul-04 4:21 PM Page 2

L1bActivity

ExtensionUnder pressure

In this activity, you are going to calculate pressure, force andarea using the pressure triangle.


F

ApForce in Area in square Pressure in newtons pernewtons (N) metres (m2) square metre (N/m2)

40 20 A

300 50 B

100 C 5

D 200 20

0.5 0.25 E

F 20 0.5

0.1 25 G

1 Copy and complete the table, calculating values for A–G.2 Louise went to see the circus. The clown on his stilts struggled to walk as he kept

sinking into the sand.

a Why do think the clown sank into the sand?b Suggest two ways he could stop himself sinking in the sand.

Which one is the most practical?c What is the pressure underneath the stilts if they have a combined area

of 0.25 m2 and the weight of the clown and the stilts is 700 N?

3 The next day Louise went back to where the circus had been, on her way to theshops. She found it difficult to walk, even in her boots, as she kept sinking into themud. Louise makes a pressure of 12 000 N/m2 on the mud and she has a weight of600 N.

a What area do her boots cover?b If she carries the shopping home the same way and the shopping weighs 100 N,

what pressure does she make on the mud?

4 Pressure is measured in N/m2 or in pascals (Pa). 1 Pa = 1 N/m2.

a What is the pressure in pascals that Louise makes on the mud on the way to theshops?

b What is the pressure in pascals that she makes on the way home, with theshopping?


L2aTeacher

activity notesPressure in liquids

Running the activityShow the pupils the three pieces of equipment without any water. Explain that you aregoing to fill each one with water and ask them to predict what will happen in eachone. Ask them to draw their predictions.

Pour the water into each of the demonstrations in turn. Ask for pupils’ observations,and discuss with them whether this is to be expected and why it happens. See if theycan link this to effects they have noticed or know about, e.g. pressure on their ears asthey go down in a swimming pool, pressure on submarines as they dive (in films),divers getting the bends, or water level effects, such as flooding or the tide coming in.

Ask pupils to draw what actually happened and then answer the questions and giveexplanations.

Expected outcomesLiquid levelPupils will see that the water level is horizontal.

Pressure at depthPupils will see that initially, the lower the hole in the side of the vessel, the greater thehorizontal range of the water ejected. If the water level in the vessel drops, then therange will drop, so if possible set this equipment up with water constantly flowing in.

Equal pressurePupils will see that the water comes out in all directions, so the pressure acts in alldirections.

PitfallsPressure at depthAs the water level changes the range will change. Cover all the holes while filling andthen keep water running in the top for long enough for pupils to see the effect.

Equal pressureAt the same depth the pressure is equal at all points and in all directions, but pupilsmay confuse this with the idea that as depth increases, pressure increases, i.e. pressureis not the same everywhere.

Answers1 a The water level is the same in each tube/is horizontal.

b Whenever water is able to flow from one place to another the surface of thewater will always be at the same level

2 a The deeper the hole below the surface, the further the water goes.b The deeper the water the greater the pressure. This is because weight of the water

above is greater.

3 a The same amount of water comes out of each hole at the same pressure.b The pressure at a point in a liquid acts equally in all directions.


Type Purpose DifferentiationPractical Demonstration to show pupils that the pressure in a liquid increases with depth, is

equal in all directions, and because of this the surface of a liquid is always level.Core


L2aTechnician

activity notesPressure in liquids

Equipment� liquid level demonstration (sometimes known as Pascal’s vases)� pressure at a depth demonstration (sometimes known as spouting cylinder)� equal pressure demonstration

For your informationRunning the activityShow the pupils the three pieces of equipment without any water. Explain thatyou are going to fill each one with water and ask them to predict what willhappen in each one. Ask them to draw in the water in the prediction section ofthe sheet.

Pour the water into each of the demonstrations in turn. Ask for pupils’observations, and discuss with them whether this is to be expected and why ithappens. See if they can link this to effects they have noticed or know about, e.g.pressure on their ears as they go down in a swimming pool, pressure onsubmarines as they dive (in films), divers getting the bends, or water level effects,such as flooding or the tide coming in.

Ask pupils to draw in what actually happened and then answer the questions andgive explanations.

Expected outcomes

Liquid levelPupils will see that the water level is horizontal.

Pressure at depthPupils will see that initially, the lower the hole in the side of the vessel, thegreater the horizontal range of the water ejected. If the water level in the vesseldrops, then the range will drop, so if possible set this equipment up with waterconstantly flowing in.

Equal pressurePupils will see that the water comes out in all directions, so the pressure acts inall directions.

Pitfalls

Pressure at depthAs the water level changes the range will change. Cover all the holes while fillingand then keep water running in the top for long enough for pupils to see theeffect.

Equal pressureAt the same depth the pressure is equal at all points and in all directions, butpupils may confuse this with the idea that as depth increases, pressure increases,i.e. pressure is not the same everywhere.


Type Purpose DifferentiationPractical Demonstration to show pupils that the pressure in a liquid increases with depth, is equal in all

directions, and because of this the surface of a liquid is always level.Core


L2aActivity

CorePressure in liquids

You are going to watch three demonstrations showing the behaviour of water andwater pressure. They are:

• liquid level demonstration

• pressure at a depth demonstration

• equal pressure demonstration.

Predicting

1 For each demonstration you are going to makea prediction. For each one, before the water isadded, think about what will happen. Copyeach diagram and draw in your prediction ofwhat will happen to the water.


2 After watching the demonstration, drawdiagrams to show what actually happened tothe water.


1 Liquid level

a Write a sentence describing the water level.b Copy and complete this sentence.

Whenever is able to flow from one place to another the

of the water will always be at the same level.

2 Pressure at a depth

a Write a sentence describing how the water came out of the holes.b Explain your observations, using the words ‘weight of water’ and ‘pressure’.

3 Equal pressure

a Write a sentence describing how the water came out of the holes.b Explain what this shows about the pressure in a liquid.


liquid level

pressure at a depth equal pressure


L2bTeacher

activity notesHydraulics

Running the activityCore: Pupils are provided with pairs of joined syringes containing water. In groups they predict what willhappen when they push one plunger in each case, drawing their predictions in the table provided. They dothe experiments and draw what happens. They answer questions on the sheet.

Help: Pupils look at the diagrams of the syringes and in groups they predict what will happen as oneplunger is pushed in each case, drawing their predictions in the table provided. They watch ademonstration of each experiment and draw what happens. They complete the statements on the sheet.

Extension: Pupils are provided with pairs of joined syringes containing water. They discuss in groups whatwill happen when they push one plunger in each case, drawing their predictions in the table provided.They do the experiments and draw what happens, using the graduations on the syringe to record thechange in the water volume in each syringe as the plunger is moved. They answer questions on the sheet.

Expected outcomesCore/Help: Pupils discover that water is not compressed in the syringe. With syringes of the same size thedistance moved in by one plunger is equal to the distance moved out by the other. With syringes ofdifferent sizes, the larger plunger always moves the shorter distance. This is because the same volume ofwater is moving from one syringe to the other.

Extension: In addition, pupils find by measurement that the increase in volume of water in one syringe isequal to the decrease in the volume of water in the other syringe.

PitfallsIf the tubes from the syringes are not firmly fixed some pupils may remove them to squirt water. Withsome groups the demonstration may be appropriate, or a set of syringes could be permanently fixed andkept for these experiments. Air trapped in the syringe will be compressed, so should be avoided.

AnswersCore:

1 Pupil predictions drawn in table. 2 Water is difficult to compress. 3 When syringes are the same sizethe plungers move the same amount. 4 When syringes are different sizes the plunger of the larger syringealways moves less. 5 a yes b yes

Help:

1 Pupil predictions drawn in table. 2 Water is difficult to compress (squeeze into a smaller space).When two syringes are the same size pushing the plunger in on one side makes the other plunger moveout the same distance.

When the two syringes are different sizes pushing the smaller plunger in makes the larger plunger moveout a smaller distance. Pushing the larger plunger in makes the smaller plunger move out a largerdistance.

When the syringes are linked by a long tube, pushing one plunger in still makes the other plunger moveout. The tube can be bent round corners and the second plunger still moves.

Extension:

1 Pupil predictions drawn in table. 2 Depends on prediction. 3 a Water is difficult to compress because the particles are touching and can’t be forced closer together. b All the particles forced out of one syringe must go into the other. There is nowhere else for them to go and they are already touching.4 a 5 cm2 × 1 cm = 5 cm3 b 5 cm3/10 cm2 = 0.5 cm 5 a yes b yes


Type Purpose DifferentiationPractical Pupils use syringes to investigate the principles of hydraulics. (The Help sheet is a

demonstration.)Core, Help, ExtensionResource


L2bTechnician

activity notesHydraulics


If some sets of syringes can be permanently set up for this experiment, then thetubing joining the two syringes can be glued to make a permanent seal. Thesize of syringes is not critical, small could be e.g. 5 cm3 and large could be 20cm3. It is not essential for all groups to use the same sizes.

� one syringe filled with water and closed permanently at the end� two small syringes (same size) filled with water and joined together� two large syringes (same size) filled with water and joined together� one small and one large syringe filled with water and joined together� two syringes joined by a long tube (about 10 cm)

For your informationRunning the activityCore: Pupils are provided with pairs of joined syringes containing water. Ingroups they predict what will happen when they push one plunger in eachcase, drawing their predictions in the table provided. They do the experimentsand draw what happens. They answer questions on the sheet.

Help: Pupils look at the diagrams of the syringes and in groups they predictwhat will happen as one plunger is pushed in each case, drawing theirpredictions in the table provided. They watch a demonstration of eachexperiment and draw what happens. They complete the statements on thesheet.

Extension: Pupils are provided with pairs of joined syringes containing water.They discuss in groups what will happen when they push one plunger in eachcase, drawing their predictions in the table provided. They do the experimentsand draw what happens, using the graduations on the syringe to record thechange in the water volume in each syringe as the plunger is moved. Theyanswer questions on the sheet.

Expected outcomesCore/Help: Pupils discover that water is not compressed in the syringe. Withsyringes of the same size the distance moved in by one plunger is equal to thedistance moved out by the other. With syringes of different sizes, the largerplunger always moves the shorter distance. This is because the same volume ofwater is moving from one syringe to the other.

Extension: In addition, pupils find by measurement that the increase in volumeof water in one syringe is equal to the decrease in the volume of water in theother syringe.

PitfallsIf the tubes from the syringes are not firmly fixed some pupils may removethem to squirt water. With some groups the demonstration may be appropriate,or a set of syringes could be permanently fixed and kept for these experiments.Air trapped in the syringe will be compressed, so should be avoided.


Type Purpose DifferentiationPractical Pupils use syringes to investigate the principles of hydraulics. (The Help sheet is a

demonstration.)Core, Help, ExtensionResource


L2bActivity

CoreHydraulics

You are going to find out about pressure in liquids, by doingsome experiments with syringes.

Predicting

1 Discuss with your group what you think will happen when youpress the plunger of the syringe in each of the sevenexperiments. Draw your predictions in the table on theResource sheet.

Obtaining evidence and presenting the results

1 Try each of the experiments in the table and fill in whathappened in each case.


Use the results of your experiments to answers to these questions:

2 Is water easy to compress (squeeze into a smaller space)?3 When the two syringes were the same size, what happened

when you pushed the plunger?4 When the syringes were different sizes, what happened when

you pushed the plunger?5 When two syringes are linked by a long tube, do they still

behave in the same way as two syringes linked by a short tube:

a when the tube is straight?b when the tube is curved round a corner?



L2bActivity

HelpHydraulics

You are going to find out about pressure in liquids, bywatching some experiments with syringes.

Predicting

1 Discuss with your group what you think will happen whenyour teacher presses the plunger of the syringe in each of theseven experiments. Draw your predictions in the table on theResource sheet.


1 Watch the demonstration of each experiment and record whathappened.


2 Use the results of your experiments to help you copy andcomplete these sentences by choosing from the words in bold.

Water is easy/difficult to compress (squeeze into a smallerspace).

When two syringes are the same size, pushing the plunger inon one side makes the other plunger move out a smaller/thesame/a larger distance.

When the two syringes are different sizes, pushing the smallerplunger in makes the larger plunger move out a smaller/thesame/a larger distance.

Pushing the larger plunger in makes the smaller plunger moveout a smaller/the same/a larger distance.

When the syringes are linked by a long tube, pushing oneplunger in still/no longer makes the other plunger move out.The tube can/cannot be bent round corners and/or thesecond plunger still/no longer moves.



L2bActivity

ExtensionHydraulics

You are going to find out about pressure in liquids, by doingsome experiments with syringes.

Planning and predicting

1 With your group predict what you think will happen when youpress the plunger of the syringe in each of the sevenexperiments. Draw your predictions in the table on theResource sheet.


1 Try each of the experiments in the table and draw whathappened in each one. Look carefully at the distance eachplunger moves in each experiment, and write the change involume (e.g. + 1 cm3 or – 0.5 cm3) of each syringe underneaththe syringe.


Use the results of your experiments to answer these questions:

2 Did your results match your predictions?3 Use the particle theory to explain the following observations:

a Water is hard to compress.b When two syringes are connected, the change in volume is

always the same in both.

4 Two syringes of water are connected. The first plunger hasarea 1 cm2 and is pushed in a distance of 5 cm.

a What volume of water is pushed into the second syringe?b How far will the second plunger, which has an area of

10 cm2, move out?

5 When two syringes are linked by a long tube, do they stillbehave in the same way as two syringes linked by a short tube:

a when the tube is straight?b when the tube is curved round a corner?



L2bActivityResourceHydraulics

Use this table to draw in your predictions for experiments 1–7and what actually happens.


Syringe full ofwater experiment

Prediction What happened

1

2

3

4

5

6

7


L2cTeacher

activity notesSqueezing liquids

Running the activityThe activity sheet should take the pupils about 10–15 minutes to complete.

Other relevant materialSkill sheet 37: Calculations

ICT opportunitiesPupils could search the Internet for hydraulic machines. Howstuffworks has(under ‘the basic idea’) animations of hydraulic cylinders – equal size and verydifferent sizes. See the Howstuffworks website.

Answers1 a 100 N/cm2

b 40 cm2

2 a 20 N/cm2

b 400 Nc The air can be compressed. This would make pressure less in the oil.

3 a 10 000 N/m2

b 50 N


Type Purpose DifferentiationPaper Pupils practise calculations involving hydraulic systems Extension


http://www.heinemann.co.uk/hotlinks/url.asp?urlid=9388

L2cActivity

ExtensionSqueezing liquids

In this activity you are going to do some calculations based on different hydraulic systems.

Hydraulic systems magnify the force you put into them. In a hydraulic system such as a brake system in a car, a small force on a small area will produce a large force on a large area, because the pressure is the same throughout the system. We can see this using the following equation:

force C=

force BFor example:

100 N=

1000 N= 1000 N/m2

area C area B 0.1 m2 1 m2

So, if the output piston is five times as big as the input piston, then the output force will be five times as big as the input force.

1 In the hydraulic pistons of a mechanical digger, a force of 1000 N is applied to the input piston, which has an area of 10 cm2.

a What is the pressure that is transmitted throughout the liquid in the hydraulic system?

b What is the area of the other piston if the force exerted on it is 4000 N?

2 In a hydraulic car jack filled with oil a force of 80 N is applied to the small piston of area 4 cm2.

a What is the pressure produced in the oil?b What is the force applied to the large piston of the system if it has

an area of 20 cm2?c Sometimes air can become trapped within this system. Why would

this make the hydraulic system less effective?

3 A car’s hydraulic brake system like the one in the diagram above has one input or master piston connected to a brake pedal, which itself is connected to two output or slave pistons on each wheel. If a force of 20 N is applied to thepedal and the input piston has an area of 0.002 m2, calculate:

a the pressure exerted on fluid within the systemb how much force is exerted on each of the four output pistons

if they each have an area of 0.005 m2.


pivot

outputcylinders

drum (fitted torear wheels)brake shoe

lining

force

brake pedal

input cylinderand piston

hydraulic fluid

to otherthreecylinders


L3aTeacher

activity notesAir pressure

Running the activity1 The Magdeburg hemispheres

You could choose to evacuate the hemispheres in advance and start by asking if anyone can pull themapart. Then show that they fall apart if the tap is opened to let the air in. For the main part of the demoshow the two halves placed together. The pump is attached to the tap and as the air is pumped out itbecomes impossible to pull the halves apart. Close the tap and remove the pump. Allow volunteers to tryseparating the two halves. (Tell them about the two teams of eight horses – see below.) Open the tap toshow that it was only the air pressure holding them together. Discuss with pupils the forces involved,drawing them on the board before getting pupils to complete the diagrams.

2 The collapsing can

This experiment can be done if you have no rotary pump by filling the can with steam and condensing it(for details, see Starter). Both are very memorable demonstrations, and you may wish to do one in thislesson, and one for revision later. The can must be airtight and there must be a good seal with the pressuretubing to the vacuum pump. Discuss with pupils how and where to draw the force arrows on the diagrams.

3 The barometer

To show that the force of the air pressure will hold up a column of water, take a tube closed at one end andfill it with water. Invert it in a trough of water. Point out that the force of the air pressure on the surface ofthe water is enough to hold the weight of the water up in the tube.

Discuss with pupils how high the tube would have to be before the air pressure could not hold up theweight of any more water. Tell them the answer is about 10.3 m. If the liquid was denser the height wouldbe less. Mercury is very heavy (13.6 times denser than water, or 13.6 times heavier than the same amountof water) and the length of the column would be about 76 cm. Show them a mercury barometer if one isavailable. They should realise that a 76 cm barometer is a lot easier to use than 10.3 m barometer. Discusswhat happens as air pressure changes (as pressure increases height increases and vice versa).

Other relevant materialThe Magdeburg hemispheres

For information and pictures of the original experiment, see ICT opportunities below. Two teams of eighthorses tried to pull apart two evacuated hemispheres. The experiment was performed in 1657 atMagdeburg, Germany, by Otto von Guericke (1602–1686), one of the burgomasters of Magdeburg. Thehemispheres were made of copper and attached to make a sphere about 35 cm in diameter. Von Guerickecalculated that a force of almost 12 000 N would be needed to pull the two hemispheres apart.

The barometer

Galileo wrote down the principles of the barometer, but it was Torricelli who constructed a water barometerin 1643 and used it to forecast the weather. The discovery of air pressure came about partly because peoplefound it was not possible to pump water more than about 32 feet up out of mines. In Torricelli’s barometerthe column of water was about 32 feet high and a little model of a man floated on the top of the water,popping out through the roof when the pressure was high, and staying inside on low pressure days, whenthe column of water was not quite as high. As this was not very practical he thought of using mercurywhich, because it is 13.6 times denser, makes the column only 1/13.6 as high – about 1 m. A unit ofpressure, the Torr, is named after him. In 1648 Pascal took a mercury barometer up a mountain and showedthat air pressure did fall with altitude, and got a unit of pressure named after him, too!

PitfallsWith all these experiments pupils often think that it is a suction force that is causing the effect. It isimportant to do a number of experiments so that they have several opportunities to rethink what ishappening. Ask questions such as, ‘When the air is let back in to the can, why doesn’t it blow up again?’(Letting air back in equalises the pressure – to provide an unbalanced force to blow it up again wouldrequire excess pressure pumped into the can, which is too dangerous to try.) Using the steam version alsohelps to dispel the idea that the pump is sucking the sides of the can inwards.


Type Purpose DifferentiationPractical Demonstrations to show pupils that air has a high pressure. Core

Resource


L3aTeacher

activity notesAir pressure (continued)

The Magdeburg hemispheres – The two halves must form an airtight seal.

The collapsing can – Cans for this purpose are supplied by Philip Harris and avoid problems caused byprevious contents of the can (e.g. contamination of the pump), or of thin cans which split as they start tocollapse, stopping the experiment proceeding further.

The barometer – It is difficult to see how a mercury barometer works when looking at a self-containedinstrument. The demonstrations with water should help.

Safety notesWhen trying to separate the hemispheres, make sure that no one will fall or come to harm if theyunexpectedly separate. Setting up a mercury barometer is both instructive and interesting. However, if it is to be done, it should be practised beforehand following the instructions set out in the CLEAPSSSafety ‘Handbook’.

ICT opportunitiesThe Magdeburg hemispheresKenyon Physics Dept. – Magdeburg Hemisphere sectionThe website has a photo of the original hemispheres.

The barometerChain Reaction, Arizona State University website – How much does the sky weigh? sectionMore details at:Barometer.ws website – history section.Project Zero at the Harvard Graduate School of Education website – The discovery of air pressure section.Picture of a water barometer:Barometer.ws website – waterbar section.This module focuses on the historical context of our discoveries about air pressure and vacuums.University of Minnesota website – Sucking students into understanding air pressure and vacuums section.

AnswersThe Magdeburg hemispheres

1 no 2 Before: arrows inside hemisphere pointing outwards and arrows outside pointing inwards;after: arrows outside the hemisphere pointing inwards. 3 Vacuum labelled inside hemispheres.4 They could not be separated. 5 They came apart easily. 6 The forces due to air pressure are high.We don’t usually notice them because they are balanced. 7 Newspaper paragraph about originalexperiment.

The collapsing can8 The can collapses. 9 Before: arrows inside the can pointing outwards and arrows outside pointinginwards; after: arrows outside the can pointing inwards. 10 Letting air back in equalises the pressure – toprovide an unbalanced force to blow it up would require more air to be pumped into the can.

The barometer11 The water stayed in the tube. 12 Because the air pressure was holding it up. 13 Water barometer: 10.3 m; mercury barometer: 76 cm. 14 Because it is nearly 14 times heavier/denser than water (13.6), sothe height of the barometer is much less. 15 a rise b fall 16 Cartoon story of Torricelli’s water barometer.









L3aTechnician

activity notesAir pressure

Equipment� Access to the Internet if pupils are going to follow up demos with research.

1 The Magdeburg hemispheres:

� Magdeburg hemispheres� rotary pump� pressure tubing to connect

2 The collapsing can: (pump method; see Starter L3 for steam method)

� rotary pump� can for experiment (e.g. Philip Harris)� pressure tubing for connecting

3 The barometer:

� glass or clear plastic tube approximately 50 cm to 1 m in length closed at one end� trough of water� safe access to mercury barometer if available

For your informationRunning the activity

1 The Magdeburg hemispheresYou could choose to evacuate the hemispheres in advance and start by asking if anyone can pull themapart. Then show that they fall apart if the tap is opened to let the air in. For the main part of the demoshow the two halves placed together. The pump is attached to the tap and as the air is pumped out itbecomes impossible to pull the halves apart. Close the tap and remove the pump. Allow volunteers to tryseparating the two halves. Open the tap to show that it was only the air pressure holding them together.

Discuss with pupils the forces involved, drawing them on the board before getting pupils to complete thediagrams.

2 The collapsing canThis experiment can be done if you have no rotary pump by filling the can with steam and condensing it(for details of this method, see Starter). Both are very memorable demonstrations, and you may wish to doone in this lesson, and one for revision at a later date. The can must be airtight and there must be a goodseal with the pressure tubing to the vacuum pump. Discuss with pupils how and where to draw the forcearrows on the diagrams.

3 The barometerTo show that the force of the air pressure will hold up a column of water, take a tube closed at one end andfill it with water. Invert it in a trough of water. Point out that the force of the air pressure on the surface ofthe water is enough to hold the weight of the water up in the tube.

Discuss with pupils how high the tube would have to be before the air pressure could not hold up theweight of any more water. Tell them the answer is about 10.3 m. If the liquid was denser the height wouldbe less. Mercury is very heavy (13.6 times denser than water, or 13.6 times heavier than the same amountof water) and the length of the column would be about 76 cm. Show them a mercury barometer if one isavailable. They should realise that a 76 cm barometer is a lot easier to use than 10.3 m barometer. Discusswhat happens as air pressure changes (as pressure increases height increases and vice versa).


Type Purpose DifferentiationPractical Demonstrations to show pupils that air has a high pressure. Core

Resource


L3aTechnician

activity notesAir pressure (continued)

PitfallsWith all these experiments pupils often think that it is a suction force that iscausing the effect. It is important to do a number of experiments so that theyhave several opportunities to rethink what is happening. Ask questions such as,‘When the air is let back in to the can, why doesn’t it blow up again?’ (Lettingair back in equalises the pressure – to provide an unbalanced force to blow it upagain would require excess pressure pumped into the can, which is toodangerous to try.) Using the steam version also helps to dispel the idea that thepump is sucking the sides of the can inwards.

The Magdeburg hemispheresThe two halves must form an airtight seal.

The collapsing canCans for this purpose are supplied by Philip Harris and avoid problems causedby previous contents of the can (e.g. contamination of the pump), or of thincans which split as they start to collapse, stopping the experiment proceedingfurther.

The barometerIt is difficult to see how a mercury barometer works when looking at a self-contained instrument. The demonstrations with water should help.

Safety notesWhen trying to separate the hemispheres, make sure that no one will fall orcome to harm if they unexpectedly separate. Setting up a mercury barometer isboth instructive and interesting. However, if it is to be done, it should bepractised beforehand following the instructions set out in the CLEAPSS Safety‘Handbook’.

ICT opportunities

The Magdeburg hemispheresKenyon Physics Dept. – Magdeburg Hemisphere sectionThe website has a photo of the original hemispheres.

The barometerChain Reaction, Arizona State University website – How much does the skyweigh? section.More details at:Barometer.ws website – history section.Project Zero at the Harvard Graduate School of Education website – The discovery of air pressure section.Picture of a water barometer:Barometer.ws website – waterbar section.

This module focuses on the historical context of our discoveries about air pressure and vacuums.

University of Minnesota website – Sucking students into understanding airpressure and vacuums section.









L3aActivity

CoreAir pressure

You are going to watch three demonstrations that were carriedout by scientists to show that air has pressure.

Watch each demonstration and answer the questions.


1 The Magdeburg hemispheres

In 1657 one of the burgomasters ofMagdeburg who was a scientist made alarge version of these hemispheres. Twoteams of eight horses tried, and failed,to pull them apart.

1 Before the air is pumped out, dothe hemispheres stick togetherwhen the two halves are joined?

2 On the diagrams on the Resourcesheet, draw arrows to show theforce of the air before the pump isswitched on and after the air hasbeen pumped out.

3 Label the space where there is noair with the scientific word for anempty space.

4 What happened when the handleswere pulled?

5 What happened when the tap wasopened?

6 What does this experiment tell usabout air pressure?

7 Imagine you were a newspaperreporter at the time of the originalexperiment. Write a paragraphabout the experiment and what itshowed.


8 What happens as the air is pumpedout of the can?

9 On the Resource sheet, drawarrows on the can before air ispumped out to show the force ofthe air. Draw the can after air hasbeen pumped out.

10 Why doesn’t the can go back to itsoriginal shape when the air goesback in?

3 The barometer

The first barometer to measure airpressure and forecast the weather wasmade in 1643 by Evangelista Torricelli.

11 What happened when the tube ofwater was inverted?

12 Why didn’t the water run out ofthe tube?

13 On the diagrams mark the height ofthe liquid in the water barometerand the mercury barometer.

14 Why is mercury used inbarometers?

15 What will happen to the height ofthe liquid in the tube if the airpressure a rises or b falls?

Torricelli made a water barometer. Thetop of it came out above the roof of hishouse. He noticed that on fine, cleardays the water level came up above theroof of his house and on wet stormydays the level dropped below the roofand could not be seen from outside. Hefloated a little model man on thesurface of the water. People came tolook at his house and see if the littleman was outside – forecasting goodweather – or inside because badweather was on the way.

16 Draw some cartoon diagramstelling the story of Torricelli’s waterbarometer for forecasting weather.


L3aActivityResourceAir pressure

Use this sheet to record your observations from thedemonstrations.

1 The Magdeburg hemispheres


3 The barometer


before the pump is switched on

to pump

after the air has been pumped out

before after

_______ m _______ cm

water fills tube water does notreach top of tube

mercury does notreach top of tube


L3bTeacher

activity notesThe pressure is on!

Running the activityCore: Pupils think about and write their predictions to the first three questions. They then work throughthe three experiments.

Experiment 1

Requires no equipment; pupils blow out their cheeks and press one with a finger.

Experiment 2

Using a balloon, pupils compare the pressure in a partially and fully blown up balloon and see how itchanges as they reduce the volume.

Experiment 3

Using a syringe, pupils compare squeezing air with squeezing water.

Help: Pupils work through the same experiments as on the Core sheet. The Help sheet provides a structurefor them to record their predictions and results.

Extension: In addition, pupils think about why gas cylinders are so small.

Expected outcomesCore: Pupils confirm that air can be compressed more easily than water and when volume goes down,pressure goes up. They explain that this is because particles are closer together at higher pressure. Becauseparticles are already touching in water, it is hard to get them to move closer to each other.

Help: Pupils confirm that air can be squashed more easily than water. Pressure goes up when the gas issquashed into a smaller volume. Water cannot easily be squeezed as the particles are already touching.

Extension: In addition pupils see that cylinders of compressed gas contain more gas in a small volume,which is a convenient way to save space.

PitfallsBalloons may burst. Closed-off water syringes are suggested so that they are not used for spraying water.

Safety notesPupils should be shown gas cylinders by the teacher. Any available could be used – a CO2 fire extinguisheror refill for fizzy drink machine.

AnswersCore/Help:

1 – 3 Pupils’ predictions. 4 As you press one cheek, you can feel the increased pressure on the other. 5 Easy to compress. 6 Harder to compress. 7 yes 8 yes 9 Air is easier to compress than water. 10 Diagrams showing force as small arrows. 11 a When air is compressed the particles move closertogether. There are more per unit volume so the pressure increases. b There is space between air particles,so it is easier to compress air, forcing the particles closer, than to compress water, where the particles arealready touching.

Extension:

12 It takes up much less space.


Type Purpose DifferentiationPractical Pupils do three short experiments to show that air can be compressed, unlike water, and

the pressure increases when it is compressed. As an extension, pupils also look at gascylinders.

Core, Help (Extension)


L3bTechnician

activity notesThe pressure is on!

EquipmentGas cylinder or cylinders (for looking at only), e.g. CO2 fire extinguisher; refillfor fizzy drink machine.

For each group:

� syringe of water with end closed off permanently� syringe of air (same size)� balloon (not inflated)

For your informationRunning the activityCore: Pupils think about and write their predictions to the first three questions.They then work through the three experiments.

Experiment 1Requires no equipment; pupils blow out their cheeks and press one with afinger.

Experiment 2Using a balloon, pupils compare the pressure in a partially and fully blown upballoon and see how it changes as they reduce the volume.

Experiment 3Using a syringe, pupils compare squeezing air with squeezing water.

Help: Pupils work through the same experiments as on the Core sheet. The Helpsheet provides a structure for them to record their predictions and results.

Extension: In addition, pupils think about why gas cylinders are so small.

Expected outcomesCore: Pupils confirm that air can be compressed more easily than water andwhen volume goes down, pressure goes up. They explain that this is becauseparticles are closer together at higher pressure. Because particles are alreadytouching in water, it is hard to get them to move closer to each other.

Help: Pupils confirm that air can be squashed more easily than water. Pressuregoes up when the gas is squashed into a smaller volume. Water cannot easily besqueezed as the particles are already touching.

Extension: In addition pupils see that cylinders of compressed gas contain moregas in a small volume, which is a convenient way to save space.

PitfallsBalloons may burst. Closed-off water syringes are suggested so that they are notused for spraying water.

Safety notesPupils should be shown gas cylinders by the teacher. Any available could beused – could be a CO2 fire extinguisher or refill for fizzy drink machine.


Type Purpose DifferentiationPractical Pupils do three short experiments to show that air can be compressed, unlike water, and

the pressure increases when it is compressed. As an extension, pupils also look at gascylinders.

Core, Help (Extension)


L3bActivity

CoreThe pressure is on!

You are going to do some experiments to find out whathappens if you try to compress air.

Planning and predicting

Write down your answers to these questions and give your reasons.

1 Do you think it will be possible to compress air?2 Do you think it will be very easy to compress air?3 Do you think it will be easier or more difficult to compress air

than to compress water?

Obtaining evidence


Experiment 1

1 Close yourmouth and puffyour cheeks outwith air.

2 Keeping yourmouth closed,push on onecheek with yourfinger.

4 What happensto the othercheek?

Experiment 2

3 Partly blow up the balloon sothat it is still quite squashy.Hold it tightly by the neck sothat it doesn’t go down.

4 Press the balloon with yourfingers.

5 Is the balloon easy or hard tocompress?

5 Blow the balloon up fully.6 Press the balloon again with

your fingers.

6 Is the balloon easy or harderto compress now, or hasblowing it up made nodifference?

Experiment 3

7 Fill the syringe with air.8 Put your finger over the end

of the syringe.9 Try to press the plunger in

and compress the air.10 Using the closed syringe of

water, try to press theplunger in and compress thewater.

7 Could you compress the air?8 Did the air resist being

compressed?9 Which was easier to

compress, the air or thewater, or was there nodifference?


10 Draw diagrams of your cheeks, a balloon and a syringe and use lots of small arrows toshow the force of the air as you compressed it.


11 Use the particle model to explain:

a what happened when you compressed the airb the difference between compressing air and compressing water.


L3bActivity

HelpThe pressure is on!

Use this sheet to help you record your predictions and results.

Predicting

Copy and complete these sentences by choosing from the words in bold.

1 I think it will/won’t be possible to squash air.2 I think it will be very easy/difficult to squash air.3 I think it will be easier/more difficult to squash air than to squash water.


4 On diagrams of yourcheeks, a balloonand a syringe, drawlots of small arrowsto show the force of the air as yousquashed it.


5 Use the particle model andthese diagrams to explain:

a what happened when you compressed the air(use diagrams A and B)

b the difference betweencompressing air andcompressing water (use diagrams A and C).

Extension

Experiment 4

11 Look at the gas cylinders.12 Estimate the volume of each one.


12 Why is gas often supplied compressed in cylinders and not at air pressure?


Extension

A B Ccompressedgas

gas liquid


L4aTeacher

activity notesPivots and levers

Running the activityThis could be set up as a circus of activities so that pairs or groups of pupils startwith different ones. Pupils think about the questions as they try moving thesuggested lever about the pivot.

Expected outcomesPupils identify pivots and levers and see that a longer lever makes the job easierbut moves further.

PitfallsModels of joints are available to buy, but if you have none direct pupils tothink about their elbow or knee joint. A moveable, not static, joint is needed.Scissors are difficult to understand. Longer handles compared to the blademakes it easier to cut. Placing the card near the pivot makes the handle leverlonger compared to the blade.

Safety notesWarn pupils not to put their fingers near hinges where they may get trapped;they should be especially careful with doors.

Answers1 – 2 Depends on pupils’ choice of joint.

3 At the hinge.

4 At the side away from the hinge.

5 At the centre of the spindle.

6 a Long lever on tap.b Short lever on tap.

7 Longest spanner.

8 Shortest spanner.

9 Handle of longest spanner moves the most.

10 Longest screwdriver.

11 Longest screwdriver.

12 Where the two blades join.

13 Near the tip.

14 A long lever.

15 A long lever moves further.


Type Purpose DifferentiationPractical Pupils look at six examples of pivots and levers and think about the length of the lever

and the distance it moves.Core


L4aTechnician

activity notesPivots and levers

EquipmentFor each group (or arrange as a ‘circus’):

� limb or joint model. Models of joints are available to buy (but if you havenone pupils can think about their elbow or knee joint). A moveable, not static, joint is needed. A complete limb or skeleton or animal jointwould be OK.

� access to cupboard door� access to tap� a nut and bolt to undo and spanners of different lengths� a tin to undo (e.g. large coffee tin) and screwdrivers of different lengths� a pair of scissors, thick (almost impossible to cut) and thin card

For your informationRunning the activityThis could be set up as a circus of activities so that pairs or groups of pupils startwith different ones. Pupils think about the questions as they try moving thesuggested lever about the pivot.

Expected outcomesPupils identify pivots and levers and see that a longer lever makes the job easierbut moves further.

PitfallsModels of joints are available to buy, but if you have none direct pupils tothink about their elbow or knee joint. A moveable, not static, joint is needed.Scissors are difficult to understand. Longer handles compared to the blademakes it easier to cut. Placing the card near the pivot makes the handle leverlonger compared to the blade.

Safety notesWarn pupils not to put their fingers near hinges where they may get trapped;they should be especially careful with doors.


Type Purpose DifferentiationPractical Pupils look at six examples of pivots and levers and think about the length of the lever

and the distance it moves.Core


L4aActivity

CorePivots and levers

You are going to look at some examples of pivots and levers.

Obtaining evidence


Experiment 1: Joint model

1 Write down the name of the joint youare examining.

2 Discuss with your partner where thepivot is in the model – the point aboutwhich the bone turns.

Experiment 3: Tap

2 Turn the tap on.

5 Is there a pivot here? If so, where is it?6 There are many different designs of

taps. Describe:

a one that is easy to operateb one that is difficult to operate.

Experiment 5: Lid and screwdrivers

4 Try to undo the lid of the tin, using thescrewdriver as a lever.

10 Which screwdriver makes it easiest toopen the tin?

11 Which screwdriver moves the mostwhen opening the tin?

Experiment 2: Cupboard door

3 Where is the pivot on the door?

1 Try gently pushing the door at differentplaces.

4 Whereabouts do you find pushing thedoor closed easiest?

Experiment 4: Nuts, bolts and spanners

3 Try undoing the nut and doing it upwith the different spanners.

7 Which spanner makes it easiest to undothe nut?

8 Which spanner makes it most difficultto undo the nut?

9 Which spanner handle moves the mostundoing the nut?

Experiment 6: Scissors

12 Is there a pivot here?

13 If something is difficult to cut, do theblades cut best near the tip of theblades or near the screw in the middle?


14 To make turning something easy do you need a long lever or a short lever?

15 What do you notice about the distance the lever moves with a larger lever?

Take carenot to trapyour fingers.


L4bTeacher

activity notesPointer precision

Running the activityPupils cut out the pointers and make a small slit at the + marks on both thepointers and the meter card. These slits could be made in advance using a sharpknife, or a suitably sized sharp pin could be provided. Pupils fix the smallpointer to the meter card with a paper fastener and experiment with settingand reading scales, swapping with a partner so that they try reading values theydon’t know in advance. (You could provide lists or cards with two or threevalues for one pupil to set and the other to read and then swap over if pupilsneed more help at this point.) They then repeat with the longer pointer so thatthey see that the same reading is much easier to make with a longer pointer. Ifyou have some suitable meters, you could have a few for pupils to look at,possibly as an extension.

Other relevant materialL4b Resource 1

L4b Resource 2

PitfallsIn trying to make holes, pupils may tear the card, or make such large holes thatthe pointer pivot point moves about.

Safety notesIf a sharp instrument is provided for making holes demonstrate to studentshow they should do so safely and supervise them closely.

AnswersCore:

1 – 3 Depends on pupils’ choices.

4 Whole numbers and those half-way between, e.g. 0.5.

5 Ones that don’t lie on the lines or half-way between them.

6 Much easier – there are smaller divisions marked and it is easier to read.

7 long

8 Magnifies the change so it is easier to measure.

Extension:

9 At the centre where the pointer is attached to the meter.

10 The movement at the end is larger because it depends on the length.

11 The small movement of the box is magnified by the arrangement of thelevers and pointer.


Type Purpose DifferentiationPaper Pupils make a card meter which can be fitted with a long or short pointer, to see how

this affects precision.Core (Extension) Resource 1 Resource 2


L4bActivity

CorePointer precision

You are going to investigate how the length of a pointer affects the precision of a measuring instrument.

Obtaining evidence

1 Cut out the pointers from Resource 1.2 Make a hole at the + sign on each pointer and on the meter card on Resource 2.3 Fix the short pointer to the meter card with the paper fastener.4 Set your meter to read 0.3.5 Swap with a partner.

1 Does their meter read 0.3?2 Do they think that your meter reads 0.3?

6 Set your meter to a value between 4 and 5.7 Swap with your partner, and read their meter while they read yours.

3 Do you both agree on the readings?4 Which readings are easy to make on this scale?5 Which readings are more difficult?

8 Change your meter by fixing the long pointer and reading the top scale.9 Repeat steps 4 to 7 with the long pointer.

6 What differences did you notice with the long pointer?7 If you are measuring something that only changes by a very small amount, would you

use a short pointer or a long pointer?8 Explain your choice.

Extension

9 Where is the pivot on your meter card?10 How is using a long pointer

similar to using a spannerwith along handle?

11 In this diagram of the aneroidbarometer the change in thesize of the box due to airpressure is very very small.How has the designer madesure that you can read thechange on the scale?


metal box – vacuum inside

pivot

air pressure

pointer

scale

air pressurepushes sides ofbox in whenpressure rises

spring pulls sidesof box out whenair pressure falls

spring

Extension

Take carewith sharpscissors

and knives.


L4bActivity

Resource 1Pointer precision



L4bActivity

Resource 2Pointer precision

5 6

6.5

7

7.5

8

9.5

108.5

9

00.5

11.5

2

2.5

3

3.5

4

4.5 5.5

5 6 7 810

90

1 2 3 4



L5aTeacher

activity notesTurning, turning

Running the activityPupils complete the activity sheet about pivots, levers and turning effects (theword moment is used only on the Extension sheet). The activity should take15–20 minutes to complete.

Practice in turning effects based on a fairground scenario.

Answers1 Pivots in middle of big wheel, middle of waltzers, wheels on ghost train,

pivot in middle of swing boat and buckets of big wheel.

2 Levers of waltzers, wheel spokes on the big wheel, levers to the buckets ofthe big wheel, arms of the swing boat, planks underneath the swing boat,train pistons.

3 Riders enjoy experiencing large forces, moving large distances, and turning.Pivots and levers can produce all of these.

4 The big wheel.

5 a A, as the force is bigger.b Increase the force (weight) or the distance.


Type Purpose DifferentiationPaper Pupils answer questions that give further practice with pivots, levers and turning

effects.Core


L5aActivity

CoreTurning, turning

In a fairground there are many moving parts with leversturning around pivots. We can find lots of examples of turningeffects. You are going to look at the picture and answerquestions about turning effects.

1 Look at the picture above and list all the different pivots youcan see.

2 Now list all the levers you can see.3 Why are pivots and levers good for making fairground rides?4 Look at the picture and suggest which moving part of the

fairground will have the largest turning effect.5 The table on the right shows the

weights of people in two buckets of the big wheel. The buckets are the samedistance from the pivot.

a Which of the buckets will have thebiggest turning effect, A or B? Explainyour answer.

b How could you increase the turningeffects around the pivots?


Bucket Total weight of bucket in newtons (N)

A 2800

B 2000


L5bTeacher

activity notesBalance

Running the activityPupils set up a beam balance so that it is balanced with no additional masses.They work through a few values of mass and distance, filling in values in thetable provided.

Expected outcomesPupils realise that there is a pattern linking the mass and distance on each sideof the pivot. The mass and distance can be the same, or the beam can be madeto balance if the product of mass and distance on each side of the pivot is thesame.

PitfallsThe beam may not balance before the masses are added. A small piece of Blu-Tack at an appropriate distance from the pivot should correct this.

Moments are not calculated here, so it is not essential to calculate force innewtons. Pupils can look for a pattern involving grams and centimetres. Thiscan be developed next lesson.

AnswersCore

1 LHS mass (weight) × distance = RHS mass (weight) × distance.

2 Try more different pairs of mass and distance.

3 If it didn’t balance you would not see this pattern, as beam would notbalance when LHS = RHS.

Extension:

4 Mass (weight) × distance.


Type Purpose DifferentiationPractical Pupils balance a mass on either side of a beam balance as an introduction to moments. Core (Extension)


L5bTechnician

activity notesBalance

Equipment� Blu-Tack or something similar for balancing a beam if it is off centre.

For each group:

� a balance beam, e.g. a metre rule graduated with eight holes (equidistant) oneach side. The centre of the beam is where the blunt round nail (for safety)is put through as a pivot. This is clamped to a stand with a boss.

� two hangers for masses� three masses (two of 100 g and one of 200 g)

For your informationRunning the activityPupils set up a beam balance so that it is balanced with no additional masses.They work through a few values of mass and distance, filling in values in thetable provided.

Expected outcomesPupils realise that there is a pattern linking the force and distance on each sideof the pivot. The force and distance can be the same, or the beam can be madeto balance if the product of weight and distance on each side of the pivot is thesame.

PitfallsThe beam may not balance before the masses are added. A small piece of Blu-Tack at an appropriate distance from the pivot should correct this.


Type Purpose DifferentiationPractical Pupils balance a mass on either side of a beam balance as an introduction to moments. Core (Extension)


L5bActivity

CoreBalance

You are going to see what happens when you try to balance two objects on a beam balance.

Equipment

• beam balance • three masses (two of 100 g and • two hangers for masses one of 200 g)

Predicting

Make a prediction about how you can use a heavy mass to balance a light mass.

Obtaining evidence

1 Set up the beam balance without any masses so that it doesn’t tip to either side.2 Place the 100 g mass on one side of the balance.3 Record the mass, and the distance from the pivot in a table like the one below.4 Balance the beam using the 100 g mass. Write in the distance from the pivot.5 Balance the beam for the other values suggested in the table. Write in the distance

from the pivot each time.



Left-hand side Right-hand side

Mass in Distance from Mass in Distance from grams (g) pivot in grams (g) pivot in

centimetres (cm) centimetres (cm)

100 20 100

100 40 100

100 20 200


1 Do you notice a pattern in your results? If so, describe what you found.

Evaluating

2 What experiments would you do to check if the pattern you found is correct?3 Why was it important to balance the beam before you started the experiment?

4 There are two blank columns in your table. What calculation might it be useful towrite in these columns?

Extension


L6aTeacher

activity notesStability

Running the activityA worksheet activity looking at different scenarios where stability is important.

PitfallsIn the crane diagram the distance is not from the weight to the pivot point atthe ground. The pivot is at the ground, but the distance is the perpendiculardistance between the weight and the pivot, i.e. the same length as the arm ofthe crane.

Answers1 a Left; toward the side with the load.

b Correctly labelled diagram: pivot = where crane reaches ground, lever = arm of crane, force = weight of block.

2 A is unstable because the moments of body, arm and leg on right(clockwise) are greater than those on the left (anticlockwise).Counterbalance by extending left arm and leaning slightly to left.B is stable because all the weight × distance from the balance point on oneside = all the weight × distance from the balance point on the other side, sothe moments are balanced.C is unstable because the weight of the body is over to the right of thebeam. Counterbalance by extending the arms in front of the body andleaning towards the beam.

3 a busb This would make the bus unstable.

4 a D is least likely to fall.b F is most likely to fall.c D is most stable. It has the largest base and all of its weight is lower,

closer to pivot point.


Type Purpose DifferentiationPaper Pupils investigate how stability of machines is linked to pivots and levers. Core


L6aActivity

CoreStability

We can see moments in action when we are trying to make things stable so they won’t fall over. When things fall over they fall around a pivot and the weight of the object acts as the force applied. You are going to answer some questions about stability.

1 Normally a crane would have a counterbalance tostop it falling over. This crane would fall over whenlifting a load.

a Which way would it fall?b Copy the diagram and label:

• the pivot around which it would fall• the lever• the force.

2 Look at the gymnasts on the beam.

For each gymnast A–C:

a say whether the gymnast would bestable or fall off the beam;

b explain your answer to a;c say how the gymnast should move to

become stable (you might want to use the word counterbalance in your answer).

3 a Which of these vehicles is the moststable?

b Why are passengers on the bus notallowed to stand upstairs?

4 Which of these vases D–G will be:

a the least likely to fall over ifknocked?

b the most likely to fall over ifknocked?

c Explain your answers to a and b.


A B C

D E F G


L6bTeacher

activity notesMore moment calculations

Running the activityPupils work through the questions on the sheet, showing all their working out.The activity should take 15–20 minutes to complete.

Other relevant materialSkill sheet 37: Calculations

AnswersCore:

1 150 × 0.5 = 75 N m.

2 400 × 0.25 = 100 N m; 400 × 0.4 = 160 N m; 400 × 0.6 = 240 N m, thereforethe 60 cm spanner should be the one he uses.

Extension:

3 8500 × 1.5 = 12 750; 12 750/4 = 3187.5 N.

4 a 450 × 1 = 450 N m.b 500 × 2 = 1000 N m.c 450/2 = 225 N m.


Type Purpose DifferentiationPaper Pupils are provided with extra practice in calculating moments. Core (Extension)


L6bActivity

CoreMore moment calculations

The size of a moment depends on the size of the force applied and the distance theforce is from the pivot. In a balanced system the sum of anticlockwise moments isequal to the sum of clockwise moments.

You are going to do some calculations of different moments.

You can calculate the size of the moment around a pivot using this equation:

moment of the force = force × distance from the pivot

N m N m

1 To finish her patio, Claudia needs to lift a paving slab using a crowbar. The pavingslab weighs 150 N and the crowbar is 0.5 m in length. What is the moment requiredto lift the slab?

2 Graham needs to undo a tight nut on his bike. He has three spanners to choose from.If he needs a moment of 200 N m to move the nut, calculate which spanner wouldbe best to use.

The table below shows the amount of force applied and the length of the spanner.

Force applied Length of spanner Moment in newtonin newtons (N) in metres (m) metres (N m)

400 0.25

400 0.4

400 0.6

Extension

3 What force would you need to balance anelephant weighing 8500 N on a seesaw if theelephant was 1.5 m from the pivot and theforce you applied was 4 m from the pivot?

4 Mary has made a machine to unload herboat, using a long lever and a large bucket.

a Calculate the moment of the bucket with a total load of 450 N if it is 1 mfrom the pivot.

b Calculate the moment of Mary, if sheapplies a force of 500 N at a distance 2 m from the pivot.

c Calculate the force Mary needs to apply to the lever to balance the weight.


Extension

1m2m


L7aTeacher

activity notesGetting balanced

Running the activityCore: Pupils use balance beams to investigate equilibrium. They use as manycombinations of weights and distances as possible (given the equipmentavailable) to balance set combinations. Questions allow them to ascertain thatthe clockwise moments are equal to the anticlockwise moments.

Help: A similar sheet with tables drawn, and easier combinations of weights.

Extension: A similar sheet with opportunities for predicting the outcome.

Expected outcomesThe pupils complete all the practical work, results tables and questions.

PitfallsEnsure that the pupils understand what a balance beam looks like. Some beamsmay be a little off centre and this can be compensated for by adding a smallpiece of Blu-Tack in an appropriate position to make the beam balance.

Safety notesWarn pupils to be careful not to drop the weights on their fingers or toes.

ICT opportunitiesIt would be possible to set up a spreadsheet for the results and subsequentcalculations.

AnswersCore:


Type Purpose DifferentiationPractical Pupils investigate equilibrium and ascertain that the clockwise moments are equal to

the anticlockwise moments.Core, Help, Extension

Weight and hole in left-hand Weight and hole in right-hand side of beam side of beam

4 N in hole 3 4 N in hole 3, 3 N in hole 4, 6 N in hole 2, 2 N in hole 6

4 N in hole 3 examples are:1 N in hole 6 + 2 N in hole 3 6 N in hole 1 + 3 N in hole 2 2 N in hole 1 + 5 N in hole 2 2 N in hole 3 + 3 N in hole 2 4 N in hole 1 + 2 N in hole 4

1 To balance the beam (i.e. to get it in equilibrium) the anticlockwise andclockwise moments have to be the same.

2 It is possible because so long as the moments are equal on each side, it willbalance.

3 It is possible because you know the moments on one side and just have toequal them to balance the other side.


L7aTeacher

activity notesGetting balanced (continued)

Help:

1 The beam balances when the product of weight and hole number on eachside is the same (i.e. clockwise moments = anticlockwise moments).

2 It is.

Extension:

1 To balance the beam (i.e. to get it in equilibrium) the anticlockwise andclockwise moments have to be the same.

2 It is possible because you know the moments on one side and just have toequal them to balance the other side.

3 3 N in hole 2, 6 N in hole 1, 1 N in hole 6 and 2 N in hole 3.

4 1 N in hole 1, 7 N in hole 7.







3 N in hole 2 examples are:3 N in hole 2, 2 N in hole 3, 1 N in hole 6, 6 N in hole 14 N in hole 1, 1 N in hole 2


L7aTechnician

activity notesGetting balanced


� a balance beam, e.g. a metre rule graduated with eight holes (equidistant) oneach side. The centre of the beam is where the blunt round nail (for safety)is put through as a pivot. This is clamped to a stand with a boss.

� 10 × 1 N slotted weights and holder� retort stand and clamps� Blu-Tack or something similar for balancing the beam if it is off centre� access to computers if pupils are to set up a spreadsheet for the results and

subsequent calculations.

For your informationRunning the activityCore: Pupils use balance beams to investigate equilibrium. They use as manycombinations of weights and distances as possible (given the equipmentavailable) to balance set combinations. Questions allow them to ascertain thatthe clockwise moments are equal to the anticlockwise moments.

Help: A similar sheet with tables drawn, and easier combinations of weights.

Extension: A similar sheet with opportunities for predicting the outcome.

Expected outcomesThe pupils complete all the practical work, results tables and questions.

PitfallsEnsure that the pupils understand what a balance beam looks like. Some beamsmay be a little off centre and this can be compensated for by adding a smallpiece of Blu-Tack in an appropriate position to make the beam balance.

Safety notesWarn pupils to be careful not to drop the weights on their fingers or toes.

ICT opportunitiesIt would be possible to set up a spreadsheet for the results and subsequentcalculations.


Type Purpose DifferentiationPractical Pupils investigate equilibrium and ascertain that the clockwise moments are equal to

the anticlockwise moments.Core, Help, Extension


L7aActivity

CoreGetting balanced

A seesaw is balanced, or in equilibrium, when the force ×distance on the left side balance the force × distance on the right side. You are going to look at different ways of getting a beam balance in equilibrium.

Obtaining evidence

1 Make a table like the one below to record yourresults.


Careful withweights – do not drop

them on your fingersor toes!

Weight and hole in left-hand Weight and hole in right-handside of beam side of beam

4 N in hole 3


4 N in hole 3 1 N in hole 6 + 2 N in hole 3

2 Set up your balance beam as in the diagram and put 4 N of weights in hole 3 on the left-hand side of the balance beam.

3 Now use a weight in a hole on the right-hand side of the beam to balance it. Find all the ways of balancing the beam, using a weight in a hole. Vary the weightand the hole. Record all the combinations in your table.

4 Draw another table like this to record your results for the next part of the experiment.

5 Repeat the experiment with 4 N in hole 3 on the left but this time use differentweights hanging in two or three different holes on the right to balance. The first example has been done for you.


1 Explain your conclusions from the investigation.2 Explain why it is possible to balance one weight on the left side with

two or three different weights on the right side.3 Explain why it is possible to predict what combinations of weights

and holes on the right balance a given weight and hole on the left.


L7aActivity

HelpGetting balanced

A seesaw is balanced, or in equilibrium, when the force ×distance on the left side balance the force × distance on the right side. You are going to look at different ways of getting a beam balance in equilibrium.

Obtaining evidence

1 Set up your balance beam as in the diagram and put 2 N of weights in hole 4 on the left-hand side ofthe balance beam.

2 Now use a weight in a hole on the right-hand side ofthe beam to balance it. Find all the ways of balancing the beam,using a weight in a hole. Vary the weight and the hole.

3 Fill in all the combinations of weights and holes in the table below.

4 Repeat the experiment with 4 N in hole 3 and complete the table below.


1 Discuss your results with your partner. What conclusions can youmake from the results of your experiments?

2 Discuss if it is possible to predict how to balance the beamwithout doing the experiment first.



2 N in hole 4


4 N in hole 3




L7aActivity

ExtensionGetting balanced

A seesaw is balanced, or in equilibrium, when the force ×distance on the left side balance the force × distance on theright side. You are going to look at different ways of getting abeam balance in equilibrium.

Equipment

• beam balance• hanger and weights

Predicting

1 Predict all the combinations of weight and holes youcould use to balance the combinations shown in thetable. Record your predictions in a table.

Obtaining evidence

2 Set up your balance beam and try all the combinations to seeif you were right.


1 Explain your conclusions from the investigation.2 Explain why it is possible to predict which combinations can

balance 1 N in hole 6 without carrying out an experiment.3 Predict which combinations of weights and holes balance 1 N

in hole 6.4 Which combinations of weights and holes have only one

possible combination that will balance them?



4 N in hole 3

3 N in hole 2





L1 Under pressure

Review learning� Show video clips of high and low pressure applications.� Pupils sort the examples into four sets: (1) Advantages of high pressure: cheese

wire, razor blade, thin beak. (2) Disadvantages of high pressure: stiletto heels. (3)Advantages of low pressure: snowshoes, caterpillar tracks. (4) Disadvantages oflow pressure: blunt knife.

Sharing responses� Pupils have calculated their pressure when wearing their shoes. They know

their weight. Now they use a given area for snowshoes or stilettos to see howthis changes the pressure.

� Stilettos: a heel of area 1 cm2. If a dancer turns on one heel, all the weight is onone heel. Ask some pupils to work out the pressure if they put all their weighton a heel area of 1 cm2.

� Snowshoes: each shoe is about 90 cm long and 30 cm wide at the widest point,one shoe has an area of about 1500 cm2. Ask some pupils to work out thepressure if they put all their weight on one snowshoe.

� In groups pupils compare their values.

Group feedback� If pupils used different types of footwear for Activity L1a (e.g. trainers, stilettos,

wellington boots) they can work in groups in which pupils all have differentfootwear to compare their results.

� Pupils should see that the area of the footwear changes the pressure. For pupilsof similar weight, pressure in shoes with stiletto heels is high but in wellingtonboots is low.

� Pupils discuss consequences of high and low pressure.

Word game� Pupils write a poem about pressure. This could be a haiku or a limerick. A haiku

has five syllables on the first line, then seven on the second, then five on thethird.

Looking ahead� Pupils work out the pressure due to weight of water on the base of a fish tank. If

there is a fish tank in one of the labs, pupils can measure the width and thelength so they can calculate the area of the tank. Tell pupils how many litres ofwater the tank holds and that a litre of water has a weight of 10 N. Ask pupils tocalculate the weight of water in the tank and the pressure of the water on thebottom of the tank.

� Extend the calculations to a swimming pool and to the ocean. Discuss whatwould happen as you added more water. Depth would increase and weightwould increase but area stays the same, so pressure on the base must increase.Ten times deeper, ten times the pressure.



Review learning

Show video clips of highand low pressureapplications. Catalyst InteractivePresentations 3

Sharing responses

Having calculated pressureof shoes with Activity L1a,pupils do this for snowshoesor stilettos, and compareresults.

Group feedback

Pupils look at differentfootwear used for ActivityL1a and discuss in groupshow this changed pressure.

Word game

Write a poem, e.g. a haikuor kenning, or a limerick,about pressure.

Looking ahead

Pupils work out thepressure due to weight ofwater on the base of a fishtank.

L1 Plenaries

L-Plenaries.qxd 13-May-04 9:52 AM Page 1


L2 PlenariesTaking the plunge

Review learning� Pupils watch a demonstration of a hydraulic system. They write down two

advantages of using a hydraulic system to transfer force.

� Pupils think about disadvantages – what could go wrong?

– Advantages: A large force can be produced. The force can be transferred aroundcorners.

– Disadvantages: A leak of fluid would stop system working. Air in fluid wouldcompress and stop force being transferred.

Sharing responses� Pupils work in groups to answer questions about pressure in liquids.

� Demonstrate how a spirit level works.

Group feedback� Pupils summarise what they found out about hydraulics and present to the rest

of the class.

� Ask pupils to think about:

– What is it about liquids which means that they can be used to make hydraulicmachines? (not easily compressed)

– What happens when equal-sized syringes are linked? (same force and distance)

– What happens when different-sized syringes are linked? (bigger force, smallerdistance for larger cylinder)

Brainstorming� Pupils work in groups looking at a diagram of the Peterborough Hydraulic Lift

Lock in Ontario, Canada.

� The sheet has a series of statements about how it works and pupils cut these intostrips and decide in which order the statements (strips) should go.

� There are two containers for the boats, one at high canal level and one at the lowlevel. The one at the top takes on a bit more water so it is heavier and when thevalve is opened it goes down, and the other goes up by the same amount – 70 ft.

WebsiteCanada’s Digital Collections – the Peterborough hydraulic lift lock section

Looking ahead� Pupils try the syringe experiments with air instead of water.� They should see that the air can be compressed so the force is not so effectively

transferred from one syringe to the other.

➔ Pupil sheet

Answers1a False; 1b False;1c True; 1d False; 2 True

Equipmenta spirit level

➔ Pupil sheet

Equipmentscissors

Answersa; g; d; i; b; h; e; c;f (c and f could bereversed, theycould be after a orafter e)


Review learning

Demonstrate a model of ahydraulic system (e.g.syringe model, or pumpmodel).

Sharing responses

Pupils work in groups toproduce true or falseanswers to questions aboutpressure in liquids as afollow up to Activity L2a.

Group feedback

Each group summariseswhat they found out abouthydraulics in Activity L2band explains to the class.

Brainstorming

Pupils look at a diagram ofthe Peterborough HydraulicLift Lock in Canada andorder a series of statementsabout how it works.

Looking ahead

Pupils use syringes to seewhether air can becompressed.




Sharing responses

1 Do these diagrams show the true level of liquid in thesecontainers?

a True/Falseb True/Falsec True/Falsed True/False

2 As you go deeper under the water the pressure increases.

True/False


a

b

c

d



Brainstorming

The Hydraulic Lift Lock (Peterborough, Ontario, Canada)

Boats cannot go up or down a waterfall; they need almost levelwater. This hydraulic lift lock can lift (or lower) boats almost 20 m.It was opened in 1904.


top river level

top chamberready todescend

bottomchamberready togo up

water

canal boat

higherpressure

lowerpressure

valve

20m

piston

A B

bottom river level

river

river

chamber B arrivedat top level – waterwill flow in

Why the top chamber is always heavier.

chamber A arrivedat bottom level –water will flow out

piston

30 cm 30 cm

canal boat


c A small amount of water flows out of the bottomchamber into the river, so that the water is level.

d The control valve is opened.

a Boats enter each of the chambers.

b The upper chamber reaches the bottom and the lowerchamber reaches the top.

i The heavier upper chamber descends, forcing the lowerchamber an equal and exact distance upwards.

h The control valve is closed.

g The chamber gates are closed.

f A small amount of water flows into the top chamber fromthe river, because it stops a bit lower. This makes it heavier.

e The two chamber gates are opened and the boatscontinue on their way.

L2 PlenariesTaking the plunge (continued)

Look carefully at the diagram and read these two statementsexplaining how the lift lock works.

1 The two boat chambers are on large pistons connected by a water pipe, making ahydraulic system. The valve between them is closed except when the lift is operating.

2 The water in the upper chamber is 30 cm deeper than the water in the lowerchamber. Because the upper chamber has more water, it is heavier.

Cut out the statements below and put them in order so that they complete the explanation of how the lift lock works.

Start with a.


Find out more about the 100-year-old lift lock at Canada’s Digital Collections website –the Peterborough hydraulic lift lock section.





L3 PlenariesPressure in the air

Review learning� Pupils look at the pictures of a deep sea diver (one going deeper than would

be possible without a pressure suit) and an astronaut. Each is wearing thespecial suit needed.

� Pupils list the ways in which the conditions are similar at the bottom of thesea and in space and the ways in which the situations are different.

� Similarities: There is a pressure difference inside and outside the suit. Thedifference in pressure would be fatal. The suit needs to be able to resist thedifference in pressure. The suit needs to be airtight. They both need to takea supply of air with them.

� Differences: Bottom of sea is high pressure, space is low pressure. If the suitleaked air would rush out in space, water would rush in at the sea floor.Higher pressure is outside the suit on sea bed but inside the suit in space.The diver would be crushed without the suit, the astronaut would explode.

Sharing responses� Pupils see the drink bottle demonstration. The water will stay in the bottle

until the lid is unscrewed, when it will pour out. (Unscrew over a sink.) Theair pressure holds the water up in the bottle, unless there is air pressure onthe top, in which case the weight of water causes it to fall out of the bottle.

� In pairs pupils discuss how to explain the effect in terms of air pressure.

� They relate the demo to the experiments seen in Activity L3a.

Group feedback� Pupils work in groups to agree the answers to the following questions

(based on Activity L3b).

Word game� Pupils complete a crossword puzzle about pressure.

Answers Across: 1 pressure; 4 area; 6 gases; 7 sea; 8 ice; 10 liquid; 11 live; 14 force; 15 pump; 16 compress. Down: 1 particles; 2 seal; 3 rise; 4 air; 5 area; 7 stiletto; 9 squeeze; 10 large; 12 vacuum; 13 volume

Looking ahead� Show pupils a jar which you are having difficulty opening.

� Ask pupils what type of force is needed (twisting or turning)? This is whatthey will be looking at next lesson.

� Ask for suggestions to open it.

� Suggestions: Use cloth, or rubber opening tool – discuss how this works, byincreasing friction. Run under tap – different expansion of container andlid. Some tools grip lid and turn handle – increased leverage.


Equipmenta small plastic fizzydrink bottle with lid,with three holes drilledin the bottom; the bottleis filled with water andthe lid replaced

QuestionsWhat evidence do wehave that air haspressure?What evidence do wehave that there is spacebetween air particles?

➔ Pupil sheet

Equipmenta jar with a tightlyfitting lid; a cloth; jaropening tools ifavailable; a chainwrench or mole grips(some tool that increasesleverage and enablesyou to open the jar)


Review learning

Look at pictures of a deep sea diverin a special pressure suit and anastronaut in a space suit. Compareand contrast the conditions. Catalyst Interactive Presentations 3

Sharing responses

Pupils look at the drink bottledemonstration and in pairsexplain it in terms of airpressure using what they havelearned from Activity L3a.

Group feedback

Pupils use evidencegathered fromActivity L3b toanswer questionsabout air pressure.

Word game

Check progress using acrossword aboutpressure.

Looking ahead

Show pupils a jar which youare having difficultyopening. Ask forsuggestions how to open it.


L3 PlenariesPressure in the air

Word game

Complete the crossword using the clues.

Across

1 What this crossword is about.4 Pressure = force/ .6 These substances can be easily compressed.7 The pressure is very high at the bottom of this.8 On thin you need to spread your weight over a large area.10 Pressure is transmitted through this.11 You need a special suit to do this when there is low or high pressure.14 Increase this to increase pressure.15 Equipment for increasing pressure in tyres.16 Scientific word for squash or squeeze.

Down

1 These are touching in a liquid, spaced out in a gas.2 You need a good to prevent gas leaking out of a high-pressure

container.3 Squash a gas to make the pressure .4 Sometimes we don’t realise this has high pressure as it is all around us.5 Sharp pins and knives increase pressure by having a small .7 These heels give high pressure.9 Do this and you’ll increase the pressure on a liquid or gas.10 Snow shoes reduce pressure by having a area.12 A container that contains nothing inside it contains a .13 For a gas, decrease this and you’ll increase the pressure.


1 2 3 4 5

6

7

8 9

10

11 12 13

14

15

16



L4 PlenariesWhere’s the pivot?

Review learning� Pupils watch video clips of bridges opening, lock gates

closing, level crossing barriers, opening, ball and chaindemolishing building. Freeze the picture at the end of eachclip so that pupils identify the pivot and the lever in eachcase.

Share responses� Pupils work in groups. They look at pictures of machines

with pivots and levers.

� Using pens in two colours, they put a ring round pivotsand line over levers.

Group feedback� Pupils discuss and prepare answers to these questions to

give to the whole class. Each group presents their answerto one of the questions.

Word game� Pupils work in pairs. One pupil reads the front of the card.

The other gives a description (or example). The first pupilthen decides if the answer is correct, according to theanswers on the back of the card.

� Pupils change over and repeat.

Looking ahead� Pupils consider the question: ‘Can we measure how good a

lever is?’

� Prompt pupils by asking, ‘What does it depend on?’

� Consider and discuss suggestions and list them on theboard.

� Conclude that it must depend on how long the lever isand how much force you put on it. Say that they will goon to measure this next lesson.


➔ Pupil sheet (photocopy on to A3 size,one for each group)

Equipmenttwo felt-tip pens for each group indifferent colours

QuestionsWhat is a pivot? (Explain anddemonstrate).

When is a lever useful?

When is a lever dangerous or adisadvantage?

➔ Pupil sheet


Review learning

Show video clips of opening bridgesand other large visual modernstructures e.g. canal lock gates.Pupils identify pivot and lever. Catalyst Interactive Presentations 3

Sharing responses

Pupils look at picturesand identify pivots andlevers.

Group feedback

Pupils discuss what theydiscovered in a circus of experiments fromActivity L4a.

Word game

Pupils answer questionsfrom cards in pairs.

Looking ahead

Pupils consider whether wecan measure how good alever is.


L1 Plenaries


L4 Where’s the pivot?

Share responses

1 Using a coloured pen, draw a circle around the pivot in each picture.2 Using a different coloured pen, draw a line over each lever.

A B

C D

E F


L4 PlenariesWhere’s the pivot?

Word game


QWhat is a hinge?

AA hinge is a pivot (pointabout which somethingturns) such as on adoor.

QGive two examples of a hinge.

ASome possible answersare: knee, elbow, doorhinge, window hinge.

QWhat is a crowbar?

AA crowbar is a tool forlevering objects. It canbe used to lift pavingstones for example.

QWhat is a ball and socket joint?

AIt is a joint that allowsyou to turn somethingin more than twodimensions like ashoulder joint (ratherthan the elbow joint).

QGive an example of a ball and socketjoint in the body.

AThe shoulder joint andthe hip joint are balland socket joints.

QWhat is a pivot?

AA pivot is the pointabout which something turns.



L5 PlenariesBalancing act

Review learning� Pupils look at the operation of a mechanical balance with two

scale pans.

� Pupils consider how the design avoids the problem of an objector weight being placed closer to the pivot – which would changethe balancing weight.

Share responses� Pupils work in pairs using white boards, taking turns to sketch

how the turning effect of a force can be balanced.

� Red book pupils: One pupil writes a force and a distance, the otherwrites another force and distance which would balance it. As avariation, the first pupil can write two different forces (ordistances) and the other can write the distances (or forces)required for balance.

� Green book pupils: One pupil draws a rock on one side of a seesaw,the other draws a different sized rock to balance it. As a variation,the first pupil can draw two different sized rocks and the othercan draw them on a seesaw in balance.

Group feedback� Pupils work in groups discussing what they discovered about

turning effects from Activity L5b.

� Pupils prepare a short conclusion and explanation, which theycan give to the rest of the class.

Word game� Play a game of hangman with the whole class to reinforce

vocabulary and spelling of the words.

� As a variation instead of sketching the man to be hanged, use abalance and add weights until it tips.

Looking ahead� Use a Lego model of a tower crane without a counterbalance to

show that as soon as it lifts something it topples over. Ask forsuggestions to avoid this and fix a counterbalance.

� Use a Lego model of a crossing barrier (or opening bridge).Discuss how heavy it is to open and how powerful the motor hasto be. Fix a counterbalance to show that the power of the motorrequired can be reduced by using a counterbalance.

Equipmentmechanical weighing scales such askitchen scales

AnswerFor most kitchen scales the pan isattached at one point to the beam,so that the force on the beamalways occurs at that point, nomatter where in the pan the objector weight is placed. (Look at theparticular design beforehand to seeif it is suitable.)

Key wordsbalance; turning effect; pivot; lever;clockwise or anticlockwise; moment(Red only); ‘force × distance’

➔ Teacher sheet

EquipmentLego crane or similar


Review learning

Show a balance with two scalepans and how it balances theturning effects of the weightsand the object.

Sharing responses

Pupils work in pairs usingwhite boards to sketch howthe turning effect of a forcecan be balanced.

Group feedback

Groups discuss what theydiscovered about turning effectsfrom Activity L5b.

Word game

Play hangman torecap key words.

Looking ahead

Show a couple of modelsof cranes (maybe Lego)with and without acounterbalance.


L5 PlenariesBalancing act

Looking aheadTeacher sheetThis requires Lego models for showing the idea of a counterbalance. If Lego isunavailable the plenary can be adapted to use K’nex or other construction toy.Alternatively, fixed models, such as a Corgi or Matchbox crane could be used,but it must be possible to tip over the crane when it is lifting a load, and to fixa counterbalance, which could be a lump of metal stuck on with Blu-Tack.

To construct the models in advance, enlist the help of two to four keen Legobuilders. There are several alternatives: They could build models usinginstructions from Lego kits (e.g. Technic II kit 1036 cards 17 and 19, or othersimilar instructions for a tower crane and a level crossing barrier); They coulddesign their own to a specification from you (tower crane with a removablecounterbalance, level crossing barrier with a removable counterbalance).

Equipment� Lego set (or similar)

Alternatively:

� crane model� load� Blu-Tack� metal counterbalance� opening bridge or barrier model

Running the activity� Set up the crane for pupils to see. Use the crane to lift a weight, which is just

slightly too heavy for it to manage without toppling forward.

� Ask for suggestions from pupils to prevent it toppling. (Note: Fixing to theground would only be suitable if you didn’t need to move the crane toanother position.)

� Fix the counterbalance and show the weight can be lifted without toppling.

� Show that as the balance is moved away from pivot or increased in weight,the crane can lift more weight.

� Show that the level crossing barrier/bridge can be balanced so that only avery small force is needed to raise it, by attaching a counterbalance behindthe pivot.


counterbalanceattached here

counterbalance



L6 PlenariesMoments in life

Review learning� Pupils look at a series of video clips of machines with

counterbalances.� Ask pupils why a crane has a counterbalance, and why is it often

one which can be moved. Answer: It is used to balance the loadbeing lifted; it can be moved to balance loads of different weight.

� Ask pupils why a level crossing barrier and a canal swing bridgeare counterbalanced. Answer: Balancing the weight of the barrieror bridge reduces the work which has to be done by the motor inlifting the barrier/bridge.

Sharing responses� Pupils stand up straight with their shoulder touching the wall,

and the side of one foot parallel to the wall and as close to it aspossible. (For a thin child, if there is a skirting board the footmay be touching, otherwise there will have to be a small gap.)

� Challenge pupils to lift the other foot off the ground withoutfalling over (twisting the body is not allowed). This is impossible.

� Ask pupils work out why they can’t do it.

Group feedback� Pupils use the conclusion that the moments each side must

balance in a practical context to balance their card duck shapefrom the Starter activity.

� Demonstrate what happens if you put the hole in the wrongplace – the duck hangs beak down or tail down.

� Demonstrate how, with the ruler standing on its edge (supportedby Blu-Tack or using stands, e.g. mirror block supports), pupilscan carefully balance the card on the edge of the ruler, with thehead on one side and tail on the other. There are several waysthey can do this. It is important that the ruler marks the linethey want to be vertical when the duck hangs from the string.

� Working in groups, pupils mark the position of the ruler on theirduck. The hole for the string will need to be on this line.

� Pupils make a hole at the top of the line and attach the string.The duck should hang without tipping up or down.

Word game� Pupils do a crossword about equilibrium.

Looking back� Pupils revise and consolidate knowledge from the unit. They can

use the Unit map, Pupil checklist, or the Test yourself questions.


AnswerWhen standing on two feet, all themoments of different parts of thebody balance about a point in themiddle, i.e. just behind the ‘tummybutton’. To balance on one footyou must lean slightly so that thetummy button is over the otherfoot, or extend an arm to shift thecentre of balance. This is notpossible if you are against the wall.

Equipmentscissors; rulers and some way ofsupporting rulers standing theiredge (e.g. Blu-Tack or mirrorstands); string for suspending theanimal

➔ Pupil sheetAnswers Across: 1 balance; 5 turning;9 pivot; 10 long; 11 clockwise;12 moment. Down: 1 beam; 2 lever;3 equilibrium; 4 right; 6 counter;7 scales; 8 force

➔ Unit map➔ Pupil checklist➔ Test yourself


Review learning

Pupils look at a video clip of a cranelifting a load, a counterbalancedcanal swing bridge opening, and alevel crossing barrier opening. Catalyst Interactive Presentations 3

Sharing responses

Challenge pupils to standstraight with side of foot andshoulder touching the wall,then lift the other foot off theground without falling over.

Group feedback

Pupils complete the starteractivity using their findingsto suspend the duck withoutit tipping beak down or taildown.

Word game

Check progressusing a crossword.

Looking back

Pupils revise andconsolidate knowledgefrom the unit.

Blu-Tack

card duck

ruler


L6 PlenariesMoments in life

Word game

Complete the crossword using the clues.

Across

1 When clockwise and anticlockwise turning effects are equal they are in.

5 What happens about a 9 across.9 The point which things will turn about.10 You can get a larger turning effect with a lever.11 A direction of turning.12 Scientific name for a turning effect.

Down

1 A type of balance.2 A machine for turning.3 When something balances it is in .4 If a child on the left-hand side of a seesaw is too heavy the child on the right side

must move to the to balance.6 With 1 across, this has a turning effect which stops you tipping over.7 Machine for weighing.8 Moment = × distance.


1 2

4

3

7 8

6

9

5

12

10

11



L7 PlenariesGetting balanced – Think about

Group feedback� Pupils work in groups to produce a statement

explaining their conclusions from the experiment.

� Pupils read out their statements and these are discussedin a teacher-led class discussion.

� If there is any confusion, draw together the correct ideasa class conclusion.

Bridging to other topics� Remind pupils of the pressure work from the beginning

of this unit. There is a similarity between the way abeam tips when unbalanced, and what happens whenthe pressure is not equalised. For example: (a) hydraulicmachines move things because the pressure is higher onone side of a piston than the other; (b) as people go upor down hills their ears ‘pop’ because air pressureoutside the ear has dropped and is different to insidethe ear. The ‘popping’ occurs as the pressure equalises.

� Ask pupils to think of other areas of science whereequilibrium is important.

� Other ideas may include: objects float when upthrustbalances weight; neutralisation will occur if the rightamount of acid is added to an alkali; eating the rightamount of calories to balance activities will not result inany weight change; populations will remain stable(balanced) with the right numbers of predators andprey. (Remember that this does not mean the numbersor amounts have to be the same – just as with moments,the weights don’t have to be the same to balance, butthe moments must be the same).


Group feedback

Pupils discuss their results in groups and write a sentence to explain howweights on either side of a pivot can be balanced by adjusting thedistance from the pivot.

Bridging to other topics

Extend the idea of equilibrium and balance to other topics which pupilsmay have already met or may meet in the future.


1 Here are some sentences about pressure. Draw lines to match thebeginnings and endings.

2 Look at these pictures of the same block standing in different ways.

a True or false? The force of the block is the same in each picture.

b True or false? The pressure of the block is the same in each picture.

c The pressure is the highest in picture .

d The pressure is the lowest in picture .

3 Look at these pictures of different footwear.

Underline the correct words to complete each sentence.

a The force is different/the same in each picture.

b The pressure is different/the same in each picture.

c The pressure is highest in picture A/B/C becausethe area of the shoe is the biggest/smallest.

d The pressure is smallest in picture A/B/C becausethe area of the shoe is the biggest/smallest.

L1 SpecialsUnder pressure


A force on a big area ...

A force on asmall area ...

Pressure ...

A BC

... depends on the force and the area over which the force is acting.

... exerts low pressure.

... exerts high pressure.

L-Specials.qxd 08-Jun-04 6:14 PM Page 1

L2 SpecialsTaking the plunge

1 Look at this diagram of two syringes.

Underline the correct words to complete eachsentence.a The pressure is different/the same through

all the liquid.b The force from the bigger plunger, B is higher/

the same/lower than the force from A.

2 Look at this diagram of syringes.Which of the syringes would youchoose to connect to the tube:a to give the biggest force?

b to give the smallest force?

3 Draw lines to match the word to its description.


A B

?

A

B

C D

E

hydraulicsystem

water pressure

liquids

Can’t be squashed because the particles are touching.

Makes use of the pressure in a liquid, which is the same in all directions.

The pressure water has because of its own weight. The deeper you go,

the bigger the pressure.


L3 SpecialsPressure in the air

1 Use words from this list to fill in the gaps. You mayneed to use some words more than once.

a You can squash a . This is becausethere are spaces between the .

b Gas is the force of the particleshitting the sides of the container.

c When a gas is squashed its decreases and its increases.

d The fast of a squashed gas is usedin machines.

e Air has its own – the higher up yougo, the lower the air pressure because the

of the air goes down.

2 Look at these gas syringes. They all startedwith the same volume of gas in them.

a Which gas syringe has the highest pressure?

b Which gas syringe has the lowest pressure?

3 Look at this drawing of a mountain.

a Where is the air pressure the lowest?

b Where is the air pressure the highest?


particles

weight pneumatic gas

volume pressure expansion

A B C


L4 SpecialsWhere’s the pivot?

1 Use some of these words to fill in the gaps.

a The point around which an object turns is called the .

b A force makes a turn around a pivot.c The further from the pivot you push a lever, the the

force you need to move the lever.

2 This man can’t get theblock to move. He’sgetting lots of advice!

Colour in green the rightsuggestions to get theblock to move.

3 Use these words to labelthe drawings of levers.You’ll need to use eachword on each drawing!


lever pivot smaller handlebigger level

Use a shorterlever.

Push down close to the

pivot.

Use a longerlever.

Push down inthe middle of

the lever.

Push down atthe end ofthe lever.

pivot

lever

force


L5 SpecialsBalancing act

1 Write true or false for each sentence.

a When two turning effects are balanced, a lever stays still.

b When two turning effects are unbalanced, a lever stays still.

2 Look at this seesaw.

Underline the correct word to complete each sentence.

a The turning effects on the seesaw are balanced/unbalanced.b The bigger turning effect is from Tim/Mahesh.c To balance the seesaw, Mahesh/Tim should move closer to

the middle.

3 Look at this seesaw.

Underline the correct word to complete each sentence.

a The turning effects on the seesaw are balanced/unbalanced.b Tim and Sarah have different/the same weights.c If Sarah moves towards the pivot, Tim’s end of the seesaw will

go up/not move/go down.


MaheshTim

Tim Sarah


1 Draw lines to match the words to the descriptions.

2 Look at this drawing of a seesaw.

a On the clockwise side the force is and thedistance from the pivot is .

The clockwise moment is ×=

b On the anticlockwise side, the force is and the distance from the pivot is .

The anticlockwise moment is ×=

c Underline the correct words to complete thesentences.

The clockwise moment is bigger than/the sameas/smaller than the anticlockwise moment.

The seesaw is balanced/unbalanced.

L6 SpecialsMoments in life


moment

counterbalance

pivot

skeleton

The point around which a lever turns.

This has pivots called joints.

Another name for the turning effect of a force.

A weight which stops something falling over.

clockwisemomentpivot

force=1 force=2

distance=1distance=2

anticlockwisemoment

Remember:moment = force × distancefrom pivot


L7 SpecialsGetting balanced

1 For each seesaw:

• fill in the numbers in the sums• do the sums• choose the correct word in the sentence.

The first line of the first one is done for you.

a


b


2 N 2 Nforce

distance

force distance××=

=......... ..................

force distance××=

=......... ..................

2 N

force distance3 2

2 N

××=

=

force

distance

......... .........

.........

force distance2 3

××=

=......... ..................



L7 SpecialsGetting balanced (continued)

c


d


e


1 N 2 Nforce

distance

force distance××=

=......... ..................

force distance××=

=......... ..................

4 N 2 Nforce

distance

force distance××=

=......... ..................

force distance××=

=......... ..................

4 N 2 Nforce

distance

force distance××=

=......... ..................

force distance××=

=......... ..................



L Specials answersPressure and moments

L1 Under pressure1 Pressure … depends on the force of an object

and the area over which the force is acting.A force on a big area … exerts low pressure.A force on a small area … exerts high pressure.

2 a trueb falsec C (balanced on a pin).d B (on a big face).

3 a the sameb differentc B, smallestd C, biggest

L2 Taking the plunge1 a the same

b higher2 a E

b A3 hydraulic system – Makes use of the pressure in

a liquid, which is the same in all directions.water pressure – The pressure water has becauseof its own weight. The deeper you go, the biggerthe pressure.liquids – Cannot be squashed because theparticles are touching.

L3 Pressure in the air1 a gas, particles

b pressurec volume, pressured expansion, pneumatice pressure, weight

2 a Bb A

3 a Cb B

L4 Where’s the pivot?1 a pivot

b leverc smaller

2 Coloured in green – Use a longer lever. Pushdown at the end of the lever.

3

L5 Balancing act1 a true

b false2 a unbalanced

b Maheshc Mahesh

3 a balancedb the samec go down

L6 Moments in life1 moment – Another name for the turning effect

of a force.counterbalance – A weight which stopssomething falling over.pivot – The point around which a lever turns.skeleton – This has pivots called joints.

2 a 2, 1, 2 × 1 = 2b 1, 2, 1 × 2 = 2c the same as, balanced

L7 Getting balanced1 a 6, 6, balanced

b 4, 6, unbalanced c 12, 4, unbalanced d 8, 8, balanced e 2, 4, unbalanced

force

lever

pivot

force

lever

pivot

lever

lever

force

force

pivot

pivot


Spe Answers.qxd 6/23/2004 9:19 AM Page 12

L1 HomeworkUnder pressure


HELP

1 Match the beginning of each sentence with the correct ending.Write out each complete sentence.

2 Some of the statements below are true and some are false. For each statement, write down ‘true’ or ‘false’.

a A nail will go into hard wood because the force of thehammer is concentrated at the point.

b A duck does not sink into the mud at the edge of the pondbecause its pressure is spread over large webbed feet.

c A fork goes into the soil more easily than a spade because theforce from the person’s foot is spread over a smaller area.

d Ben and Bob weigh the same but Ben has bigger feet, so Benwill make deeper footprints on a sandy beach than Bob.

CORE

3 The surface areas of differentanimals’ feet are given in thetable on the right. The animalsare elephant, dog, guinea pigand polar bear.

Beginnings Endings

A A big elephant does not sink into 1 because it has a pointed end.the mud

B A dart goes into a dartboard very 2 because this gives them a large surface easily so they will not pierce people’s skin.

C A clown on stilts makes a deeper 3 because this spreads the force and mark on the ground than a clown stops the pin from going into your without stilts thumb.

D Children’s Robin Hood sets have 4 because its feet have a large area.rubber stickers on the arrows

E A drawing pin has a flat top 5 because the stilts have a very small surface area.

Animal Surface area of each foot in cm2

A 9

B 1500

C 1

D 600

L-Homework.qxd 08-Jun-04 3:14 PM Page 1

L1 HomeworkUnder pressure (continued)

a i Animal B is an African elephant. Suggest why it is anadvantage for an elephant to have such a large foot.

ii What is the total surface area of all the elephant’s feet?

iii If the total force exerted by the elephant on the ground is300 000 N, what is the total pressure on the ground fromall four feet? Show how you reached your answer.

b i Which animal might be a polar bear?

ii Explain your reasoning.

EXTENSION

4 Joe weighs 75 N and has a mountain bike, which weighs 10 N.He usually pumps up the tyres quite hard. When it is very muddyhe lets some air out of the tyres because he thinks this makes thebike easier to ride.

The table shows the area of each tyre that is in contact with theground.

In the calculations below, give your answers to the nearest wholenumber.

a Calculate the pressure exerted by each tyre on the groundwhen Joe is riding his bike

i when it is inflated normally

ii when some air has been let out.

b In which state will the tyres make the deepest marks in theground?

c Joe went on a diet and lost some weight. Calculate Joe’s newweight, to the nearest Newton, if the pressure exerted byeach tyre on the ground with both tyres fully inflated is 6650 N/m2.


State of the tyre Area in contact with the ground (m2)

Normal 0.12 x 0.05

Deflated 0.13 x 0.07


L2 HomeworkTaking the plunge

HELP

1 The diagram shows water leaking from a can.

a At which labelled point A, B orC is the water pressure greatest?

b Why is the pressure at point Bgreater than the pressure atpoint A?

c i What will happen to thestream of water comingfrom point C as the canempties?

ii Explain why this will happen.

d i If there was a hole at point D, where would the stream of water hit the table?

ii Explain why you have chosen this point for the water to hit the table.

CORE

2 Look at the diagram of the two syringes connected together. Plunger A is pushed in.

a i What can you say about the force exertedon Plunger B?

ii Explain your answer.

b i What can you say about the pressure on Plunger B?


c i What would you need to do to increase the force on Plunger B?

ii Explain why this would increase the force on B.

d A car braking system uses a fluid to transmit the force from the brake pedal to the brakes. When the driver presses the brake pedal, the brakes are pressed against the wheel to slow it down.

i What do we call a system that uses liquids to transmit force from one place to another?

ii In the car braking system, would the brake pedal plunger be like Plunger A or Plunger B?

iii Explain the reasons for your choice.


A

B

C

X Y ZD

A B


L2 HomeworkTaking the plunge (continued)

EXTENSION

3 Look again at the diagram in question 2.

a Plunger A has an area of 0.5 m2 and the area of Plunger B is 0.1 m2.

i James pushes on plunger A with a force of 50 N. Calculate the pressure exerted on Plunger B.

ii Now calculate the force on Plunger B.

b i The right-hand syringe is replaced with another one. The new plunger has an area of 0.2 m2. What is the force on Plunger B now? (Hint: you do not need to actually calculate it!)

ii Explain your reasoning.


A B


L3 HomeworkPressure in the air

HELP

1 Copy and complete the following sentences:

a When a gas is squashed its particles .

b When a gas is squashed its pressure .

c When a gas is squashed its volume .

d Gases exert a pressure on the inside of their containerbecause .

2 Ahmed buys a helium balloon at a fair. He lets it go and it risesup into the air.

a What happens to the pressure of the air outside the balloonas it goes higher?

b What happens to the volume of the balloon as it goes higher?

c Wherever the balloon is, what can you say about the pressureof the air inside and outside the balloon?

CORE

3 Freddy is a jet fighter pilot. His aircraft can fly over 12 000 mabove sea level. He wears a special, pressurised suit when he flieshis aircraft. The suit fills up with extra air as Freddy gets higherand higher.

a i What is different about the air pressure at 12 000 mcompared with at sea level?

ii Explain why it is different.

b i What problem would Freddy have, if he did not wear hispressurised suit?

ii Explain how his pressurised suit helps him with thisproblem.



L3 HomeworkPressure in the air (continued)

4 Sue drives her car along a motorway. The air causes a pressureagainst the windscreen.

a How does the air cause a pressure against the windscreen?

b i What happens to this pressure when Sue accelerates?

ii Why does this happen?

c Suggest why the glass in jet aircraft windscreens has to bethicker than the glass in a normal car windscreen.

EXTENSION

5 Rheinhold Messner was the first person to climb Mount Everestwithout breathing from an oxygen cylinder.

a Why would most mountaineers need to use an oxygencylinder to help them climb Mount Everest?

b i A gas cylinder is very small. How is it possible to fitenough air into the cylinder to last for several hours?

ii What can you say about the particles in the cylindercompared with those outside it?

c i What would happen if the valve on the cylinder snappedoff, so that the inside was open to the atmosphere?

ii Explain why this would happen.

6 Air can be used inside a pneumaticshock absorber for a car wheel.When the wheel goes over abump the piston is pushed intothe cylinder.

a What happens to the airpressure inside the shockabsorber when the car goesover a bump?

b Suggest how this helps the car to reduce the shock ofthe bump.


car body

shock absorber

airtightseal

air


L4 HomeworkWhere’s the pivot?

HELP

Look at these pictures of some everyday objects.

1 a What are points X and Y called?

b George needs to change the wheel on his lorry. He tries to undo the wheel nuts using spanner A. He cannot move the nuts.

i Why can’t George move the wheel nuts?

ii Which other object might solve the problem?

iii Why might this object work better?

iv He still cannot undo the nuts. He has a long piece of pipe handy. What else could he do?

v Now he is successful. Explain why.

CORE

2 The diagram shows the brake on a bikehandlebar. The brake lever is attached to a cable that pulls the brakes onto thewheel.

a Where is the pivot of the lever?

b Where should the cyclist apply herforce to give the easiest brakingaction?

c i How would the force on the brakesbe changed if the brake lever wasshortened?

ii What must the cyclist do to keep the same force on the brakes, even thoughthe lever is shorter?


20 cm

spanner A

40 cm

spanner B

X YSally Sammy

handlebar

brake lever

brake cable


L4 HomeworkWhere’s the pivot? (continued)

3 Bob the plumber wants to turn off the water at the stop-tap outside a house. He uses a special tool to do this.

a Which letter shows the position of the pivot?

b Bob pulls on the tool at point X but the tap does notmove.

i Describe two ways in which Bob can increase theturning force on the tool.

ii The tap still does not move. Bob hits the tool hardwith a large hammer at point Y. Now the tapmoves. Explain why the tap moves now.

EXTENSION

4 Look at the scissors on the right.

a Where is the pivot on the scissors?

b How would you redesign the scissors to increase theforce on the cutting blades?

c i Where, on the cutting blades, will the cuttingforce be greatest? (Hint: on a seesaw, a heavyperson can sit closer to the pivot than a lighterweight person.)

ii Explain why this point has the greatest force.

5 Dimitri is a gymnast. He trains by doing pull-ups on a highbar. His friend Janni also does pull-ups. Dimitri’s arms arelonger than Janni’s. They both weigh the same and theirarm muscles exert exactly the same force. The diagramshows how he does this.

a Where, in the gymnast’s arm, is the pivot?

b i Which of the gymnasts will find it harder to do eachpull-up?

ii Explain why this gymnast will find it harder.


Dimitri on his bar

Z

X Y

Tap fitsin here

Bob's specialtool


L5 HomeworkBalancing act

HELP

1 The diagram shows a bird perched on a TV aerial.

a i What happens to the aerial when the birdlands on it?

ii What name is given to the effect of thebird’s force on the aerial?

iii What force on the bird is causing this effect?

b i What will happen if the bird moves towardsthe centre of the aerial?

ii Why will this happen?

c i What will happen if another bird lands on the opposite side of the aerial?

ii Why will this happen?

CORE

2 Look at Sally and Sammy on a see-saw.

a i Sally and Sammy weigh the same.Where should they sit to make thesee-saw balance?

ii Explain why this will make it balance.

b i Sammy’s dog jumps onto her lap.What will happen to the see-saw?

ii Explain why this will happen.

iii What could Sammy do to make thesee-saw balance again?

iv What could Sally do to make it balance?

3 Think about the picture of the crowbar.

a Where should John push on the crowbar tohave the greatest effect?

b In which direction must he push?

c Explain why this will be the best way to usethe crowbar.

d Describe where, on the crowbar, the pivot would be.


Sally Sammy

Y

John with his crowbar


L5 HomeworkBalancing act (continued)

EXTENSION

4 The diagram shows a balanceset that is often used in infantschool maths. You may haveused one yourself several years ago. It is used to teachchildren how numbers relateto each other. For example, ifyou put a single tag onto thenumber 6 peg on the left, youcould balance it with two tagson the number 3 peg on theright. This shows that two lotsof three equals six.

a Teresa is using a number balance to test out ideas about moments. Each number is 1 cm away from the ones next to it. Number 1 is 1 cm away from the pivot. All the tags weigh 5 N.

i With the balance set up exactly as shown in the picture, calculate the value for the anticlockwise moment, on the left-hand side. (Hint: Be careful about the unit you give for the moment!)

ii What would be the value of the moment of the clockwise force on the right-hand side to balance the set-up in a i ?

iii How many tags must Teresa hang on the number 8 mark on the right-hand side to balance the set-up in a i ?

b Teresa removes all the number tags. Then she hangs one tag on the number 10 mark, on the left-hand side.

i Calculate the anticlockwise moment produced by this tag.

ii Suggest one way in which Teresa could make the beam balance again, without changing the left-hand side.

c Teresa removes all the tags.

i What would happen to the beam if she now hangs two tags at the number 3 mark on the left-hand side and four tags at the number 2 mark on the right-hand side?



1 2 3 4 5 6 7 8 9 1012345678910

Pivot

two 5 N tags

L-Homework.qxd 22-Jul-04 3:00 PM Page 10

L6 HomeworkMoments in life

HELP

1 Tim is learning to balance for his family’s circus act. He is balancing on his left legwith his arms stretched out on each side. His body is leaning over to the left.

Tanya throws him a heavy juggling club.Tim catches it in his left hand. Heoverbalances and falls over.

a What do scientists call the balancepoint in Tim’s body?

b i Which way must Tim stretch hisright leg to stay in balance?

ii What would happen if he did notdo this with his right leg?

c When Tim catches the club his balance changes.

i What sort of effect does the weight of the club produce?

ii Which way does he fall?

iii Why does he fall in this direction?

iv What could he do to stop himself from falling over?

CORE

2 The diagram shows a security barrier outside a police station car park. The beam is exactly balanced and is not resting on the right-hand support pole.

a What is point R called?

b Why is point R very important for calculating moments?

c i What is object P usually called?

ii What is the purpose of object P?


STOP

500 N

P

R


d i Object P is suspended from the barrier 0.5 m to the left of point R. Calculate the anticlockwise moment produced by the force.

ii The beam to the right of point R is 5 m long. Calculate the downward force of the beam at its right-hand end.

e i What would you do to object P if the beam was made a metre longer on the right?

ii Explain why this would help.

EXTENSION

3 The diagram shows an oldindustrial lever used to stamp out pieces of metal from a metal sheet. Theoperator pushes down on the right-hand end of thehandle. The machine is shown at rest. The downward force of 50 N is just the weight of the handle.

a Calculate the moment, inNm, of the 50 N weightabout the pivot.

b When the machine is at rest, what is the downward force exerted by the punch?

c To punch out a piece of metal requires a total downward force of 1000 N on the punch. What is the additional force that the operator must use to push down on the handle?

d The operator now needs to stamp a mark onto the punched out piece of metal. He changes the punch for a patterned stamp. The stamp has a surface area of 5 cm2. He pushes down on the handle with the same force asbefore.

i Calculate the pressure that this force exerts on the punched out disc.

ii Explain why the stamp only makes an impression on the metal but the punch cuts right through it.

L6 HomeworkMoments in life (continued)


Punch

800 cm

100 cm

50 N

View of the punch from below

steel cutting edge

hollow centre

Pivot


L1Homework

mark schemeUnder pressure


HELPQuestion Answer Mark

1 A – 4; B – 1; C – 5; D – 2; E – 3. 44 or 5 correct = 4 marks, then 3 correct = 3 marks etc.

2 a True 1

b True 1

c True 1

d False 1

Total for Help 8

COREQuestion Answer Mark

3 a i Elephants weigh a lot. 1The large foot spreads the elephant’s weight/force over a large area, 1reducing the pressure on the ground. 1

ii 4 × 1500 = 6000 cm2 1

iii Pressure = 300 000/6000 1= 50 N/cm2 1 + 1Mark is for correct setting. Carry forward any error from part ii.Award 1 mark for the answer and 1 mark for the correct unit.

b i Animal D. 1

ii It has large feet to spread its weight/force over a large area 1but is not as big as an elephant. 1

Total for Core 10

EXTENSIONQuestion Answer Mark

4 a i Pressure = 85/(0.12 × 0.05) ÷ 2 1= 7083 N/m2 1Award mark for correct results from incorrect data.

ii 85/(0.13 × 0.07) ÷ 2 1= 4670 N/m2

Award mark for correct results from incorrect data.

b Normal/Fully inflated. 1

c Weight = 6650 × 0.12 × 0.05 × 2 1= 79.8 N (accept 80 N) 1Less weight of bike = 79.8 – 10 1Joe’s new weight = 69.8 N 1Answer must include the correct unit. Award a maximum of 1 mark for correct calculation from incorrect data.

Total for Extension 8


L2Homework

mark schemeTaking the plunge



1 a C 1

b There is more water/a bigger weight of water pushing down on B. 1

c i It will die away/get slower/not squirt as far/get less and less. 1

ii The weight of water pushing down is getting smaller 1so the pressure is going down. 1

d i To the right of Z/further away than the others. 1

ii The weight of water is larger than for all the others 1so the pressure is greater. 1

Total for Help 8


2 a i It is smaller than the force on Plunger A. 1

ii The pressure of the liquid is acting on a smaller area in B. 1

b i It is the same as the pressure on Plunger A. 1

ii The particles are touching each other 1so they all move together when you squeeze it. 1

c i Make it larger/use a bigger syringe. 1

ii The pressure would act on a larger area, increasing the force. 1

d i A hydraulic system. 1

ii Plunger B. 1

iii A small force on the brake pedal would be transmitted as a larger force on the brake. 1

Total for Core 10


3 a i Pressure on A = Pressure on B 1so pressure on B = 50/0.5 1= 100 N/m2 (Unit required for the mark to be awarded). 1

ii Force on B = 100 × 0.1 1= 10 N (Unit required for the mark to be awarded). 1

b i 20 N 1

ii Doubling the area doubles the force 1because the pressure is constant/the same. 1



L3Homework

mark schemePressure in the air



1 a When a gas is squashed its particles get closer together. 1

b When a gas is squashed its pressure increases/goes up. 1

c When a gas is squashed its volume decreases/goes down. 1

d Gases exert a pressure on the inside of their container because they hit the sides of the container 1and the force creates the pressure. 1Underscore is pupil response. Accept equivalent alternatives.

2 a It gets less/decreases. 1

b It increases/the balloon gets larger. 1

c They are the same inside and outside balloon. 1

Total for Help 8


3 a i It is lower at 12 000 m/higher at sea level. 1

ii There is less weight of air pushing down at altitude/more weight of air pushing down at sea level. 1

b i His body would try to expand. 1

ii The extra pressure around his body pushes against him 1preventing his body from expanding. 1

4 a The air particles hit the windscreen. 1

b i It will increase. 1

ii More particles will hit the screen each second 1and the particles will hit the screen faster. 1

c So that the pressure does not break the glass. 1

Total for Core 10


5 a There is not much air/not enough air to breathe at high altitudes. 1

b i The air is compressed. 1

ii They are closer together. 1

c i Most of the air would rush out. Do not credit all the air rushes out. 1

ii It would make the pressure inside and outside the cylinder the same. 1

6 a It increases. 1

b It absorbs the force of the bump 1as the air particles are compressed/pushed closer together. 1



L4Homework

mark schemeWhere’s the pivot?



1 a Pivots 1

b i The spanner is too short 1he cannot get enough force with this spanner. 1Accept equivalent responses.

ii Spanner B. 1

iii It is longer 1so will produce a bigger force. 1

iv Put the pipe over the spanner handle to make it longer. 1

v The further the force is away from the pivot, the less force is needed. 1

Total for Help 8


2 a Where the brake lever is attached to the handlebar. 1

b At the end of the lever. 1

c i It would be smaller. 1

ii Pull them on harder. 1

3 a Point Z. 1

b i He could pull harder; he could pull on point Y instead. 2

ii The hammer is heavy 1so it provides a large force on the end of the tool/at point Y 1which makes the turning force big enough to move the tap. 1

Total for Core 10


4 a Where the blades are joined together. 1Accept equivalent responses.

b Make the handles longer/make the blades shorter. 1

c i Closest to the pivot. 1

ii It must be greatest near the pivot, to balance the force on the handles which are further away. 1

5 a The elbow. 1

b i Dimitri 1

ii His weight is further from the pivot 1so it will be harder to lift his body. 1



L5Homework

mark schemeBalancing act



1 a i It bends 1down/to the right. 1

ii The turning effect. 1

iii Gravity 1

b i The aerial will bend less. 1

ii The turning effect is less. 1

c i The aerial will bend less/bend back/straighten up. 1

ii The other bird’s turning effect will balance the original bird. 1

Total for Help 8


2 a i The same distance either side of/from the pivot. 1

ii The turning effect will be the same on both sides so it will be balanced. 1

b i It will go down on her side. 1

ii The turning effect on her side is now greater than that on the other side/the turning effects have become unbalanced. 1

iii Move towards the pivot. 1

iv Move away from the pivot. 1

3 a At the end furthest from the box. Accept equivalent responses. 1

b Downwards 1

c It will produce the greatest turning effect. 1

d Where the crowbar rests on the side of the box. 1Accept equivalent responses.

Total for Core 10


4 a i 4 × 10 1= 40 Ncm 1

ii 40 Ncm 1

iii 1 (or show working 8 × 5 = 40) 1

b i 10 × 5 = 50 Ncm 1

ii Either one tag at the number 10/10 cm mark or two tags at the number 5/5 cm mark. 1

c i It would go down to the right/turn clockwise. 1

ii The moment on the right-hand side is greater than the moment on the left-hand side. 1



L6Homework

mark schemeMoments in life



1 a The pivot/centre of gravity/centre of mass. 1

b i To the right/outwards/away from him. 1

ii He would overbalance 1to the left. 1

c i A turning effect. 1

ii To the left. 1

iii The turning effect on the left has increased. 1

iv Stretch out his right leg further/lean to the right. 1

Total for Help 8


2 a The pivot. 1

b The moment = the force × the distance from the pivot. 1Accept equivalent alternative responses.

c i A counterweight. 1

ii To balance the turning effect of the weight at the other end. 1

d i Moment = 500 × 0.5 1= 250 Nm (mark must include correct numerical value and the correct unit) 1

ii Force = 250/5 1= 50 N 1

e i Increase its weight. 1

ii This would increase the moment/balance the larger moment on the right. 1Accept equivalent alternative responses.

Total for Core 10


If errors are carried forward, do not penalise twice in these consecutive calculations.

3 a Moment = 50 × 0.8 1= 40 Nm 1

b Force = 40/0.1 1= 400 N 1

c Extra force needed at B = 1000 – 400 = 600 N 1Moment at B = 600 × 0.1 = 60 Nm 1Extra force at A = 60/0.8 = 75 N 1or a calculation based on the total amount of force required.

d i Pressure = 1000/5 = 200 N/cm2 (both value and unit must be correct) 1

ii Punch has a much smaller surface area 1so the pressure is much greater than for the stamp. 1



L Test yourselfPressure and moments

1 Which unit is used to measure pressure? Underline the correct answer.

newtons per square metre newtons

seconds metres

2 Underline the objects that create low pressure by spreading out force over a large area.

skis tractor tyres football boots

ice skates snowshoes javelin

3 For each pair of diagrams, tick the one that will result in the larger pressure.

4 A force of 10 N acts upon an area of 2 m2. What would the pressure be? Underline the correct answer.

a 5 N/m2 b 10 m2 c 10 N/kg d 20 N m2

5 For each of the following sentences, underline true or false.

a Liquids cannot be compressed. true/false

b Gases cannot be compressed. true/false

c The pressure is increased if more gas particles are added to a container. true/false

d The fewer times the gas particles hit their container, the higher the pressure. true/false


force force

force

force

a

b

Test-Qust.qxd 6/25/2004 10:33 AM Page 33

L Test yourselfPressure and moments (continued)

6 Look at the diagrams of syringes. A force is applied on the left-hand plunger.

a Which pair of syringes will produce the larger force at A?

b What is this system called?

7 Label the pivots on the drawings below.

8 Look at the diagram of a water tower.

a At which point will the water be under the most

pressure?

b At which point will the water be under the least

pressure?

9 The arm is an example of a lever. What is the name ofthe pivot of the arm?

Underline the correct answer.

a biceps b triceps c forearm d elbow

10 a What is the name for the effect a force has when it is applied to one end of a

lever and tries to turn the lever?

b What two things affect how easy it is to use a lever?

1

2


A

A

X

Y

force force

force force

seesaw car door door handle

A

B

C


L Test yourselfPressure and moments (continued)

11 When you use a pair of scissors, it is easier to cut card with the tip of the scissors.

Is this true or false?

12 For each pair of diagrams, tick the one that will result in the bigger turning effect.

13 What will happen to the seesaw whenboth people get on? Choose from theanswers below.

A It will turn in a clockwise direction.

B It will balance.

C It will turn in an anti-clockwise direction.

The correct answer is .

14 When anti-clockwise moments are equal to clockwise moments, a beam will balance.

Use this idea to calculate thesize of the force needed on the right-hand side to balancethe beam in the diagram.

The force needed is .


force applied force applied

force appliedforce applied

a

b

10 N

? N

left-hand side right-hand side

6 cm3 cm


LTest yourself

AnswersPressure and moments

1 Which unit is used to measure pressure? Underline the correct answer.

newtons per square metre newtons

seconds metres

2 Underline the objects that create low pressure by spreading out force over a large area.

skis tractor tyres football boots

ice skates snowshoes javelin

3 For each pair of diagrams, tick the one that will result in the larger pressure.

4 A force of 10 N acts upon an area of 2 m2. What would the pressure be? Underline the correct answer.

a 5 N/m2 b 10 m2 c 10 N/kg d 20 N m2

5 For each of the following sentences, underline true or false.

a Liquids cannot be compressed. true/false

b Gases cannot be compressed. true/false

c The pressure is increased if more gas particles are added to a container. true/false

d The fewer times the gas particles hit their container, the higher the pressure. true/false


forcea

b

force

force

force

�

�

Test-Ans.qxd 16-Jun-04 2:56 PM Page 33

LTest yourself

AnswersPressure and moments (continued)

6 Look at the diagrams of syringes. A force is applied on the left-hand plunger.

a Which pair of syringes will produce the larger force at A?

b What is this system called?

7 Label the pivots on the drawings below.

8 Look at the diagram of a water tower.

a At which point will the water be under the most

pressure?

b At which point will the water be under the least

pressure?

9 The arm is an example of a lever. What is the name ofthe pivot of the arm?

Underline the correct answer.

a biceps b triceps c forearm d elbow

10 a What is the name for the effect a force has when it is applied to one end of a

lever and tries to turn the lever?

b What two things affect how easy it is to use a lever?

1

2 distance from pivot

force applied

turning effect or moment

A

C

hydraulic system

Y


A

A

X

Y

force force

force force

seesaw

pivot

car door door handle

pivot pivot

A

B

C


LTest yourself

AnswersPressure and moments (continued)

11 When you use a pair of scissors, it is easier to cut card with the tip of the scissors.

Is this true or false?

12 For each pair of diagrams, tick the one that will result in the bigger turning effect.

13 What will happen to the seesaw whenboth people get on? Choose from theanswers below.

A It will turn in a clockwise direction.

B It will balance.

C It will turn in an anti-clockwise direction.

The correct answer is .

14 When anti-clockwise moments are equal to clockwise moments, a beam will balance.

Use this idea to calculate thesize of the force needed on the right-hand side to balancethe beam in the diagram.

The force needed is .5 N

C

false


force applied force applied

force appliedforce applied

�

�

a

b

10 N

? N

left-hand side right-hand side

6 cm3 cm


LEnd of unit test

GreenPressure and moments

1 a Copy this diagram and label the pivot. 1 mark

b Which way will this beam turn, clockwise or anti-clockwise? 1 mark

2 a Which part of the body is the weight-lifter using as a pivot? 1 mark

b Which part of his body is the lever? 1 mark

c Why does spreading her arms help the gymnast stay balancedon the beam? 1 mark

3 Which of the following beams will balance? 2 marks


A B

C D

J-L-EUTest.qxd 18-Jun-04 11:01 AM Page 17

LEnd of unit test

GreenPressure and moments (continued)

4 Vince was trying to get the lid off an old tin of paint. He had achoice of three tools to use, which are shown below.

a Which tool should he choose to make the job easiest? 1 mark

b Explain your answer. 1 mark

5 A large plastic storage box is to be kept on a shelf in a warehouse.The warehouse manager needs to decide which surface will create the smallestpressure on the shelf.

a Which side would create the greatest pressure on the shelf? 1 mark

b Which side would create the smallest pressure on the shelf? 1 mark

c Give the reason for your answer to b. 1 mark

6 a Which of these diagrams show a gas under the highest pressure? 1 mark

b What two things could you do to reduce gas pressure? 2 marks

7 A snowboarder and a skier are arguing over who will exert the lowerpressure. Both people have a weight of 800 N, the skis have a totalarea of 0.3 m2 and the snowboard has an area of 0.5 m2.

a Will the snowboarder or skier exert the lower pressure? 1 mark

b Give the reason for your answer. 2 marks

8 A car braking system uses brake fluid to transmit the pressure fromthe brake pedal to the car wheels. Explain, using the particle theory,why a liquid is used in a car braking system and not a gas. 2 marks


A B C

BA

C

A B C


LEnd of unit test

GreenPressure and moments (continued)

9 Ceri is experimenting with a balanced beam. It has two sliding masses onit. Ceri finds that if she moves the mass on the left side of the beam, thebeam tips unless she moves the right hand mass to make it balance again.

a What factor (variable) is being changed in the experiment? 1 mark

Ceri makes a results table, and records the distance between eachmass and the pivot as she gets the beam to balance.

b i What pattern was Ceri able to see in her results. 1 markii Ceri thought that one of her results did not fit the pattern.

What reason did she have for saying this? 1 mark

Ceri makes a prediction that there is a rule about balanced beams. It is thatthe mass on one side of the pivot times its distance from the pivot is equalto the mass on the other side of the pivot times its distance from the pivot.

Ceri removed the right sliding mass from the beam and replaced it with onethat had twice the mass.

c i What did Ceri predict about how her results from her firstexperiment might change? 1 mark

ii Complete Ceri’sresults table with the results you would expect her to get. 1 mark


left mass right masspivot

Distance between left mass Distance between right massand pivot (cm) and pivot (cm)

6 6

15 14

17 17

25 25

Distance between left Distance between rightmass and pivot (cm) mass and pivot (cm)

6

7

11

3


LEnd of unit test

RedPressure and moments

1 Vince was trying to get the lid off an old tin of paint. He had a choiceof three tools to use, which are shown below.

a Which tool should he choose to make the job easiest? 1 mark

b Explain your answer. 1 mark

c Give another factor that affects the size of the turning effect. 1 mark

2 a Which of these beams will balance? 2 marks

b Why does spreading her arms help the gymnast stay balancedon the beam? 1 mark

3 A large plastic storage box is to be kept on a shelfin a warehouse. The warehouse manager needs todecide which surface will create the lowestpressure on the shelf.

a Explain why side C will exert the lowestpressure. 1 mark

b The box has a weight of 480 N. Calculate the pressure side C will exert. 2 marks


A B C

3 cm2 cm

1 cm

2 cm2 cm1 cm2 cm

2 cm2 cm

A B

C D

4 m3 m

1 m

BA

C


LEnd of unit test

RedPressure and moments (continued)

4 a A car braking system uses brake fluid to transmit the pressure fromthe brake pedal to the car wheels. Explain, using the particle theory,why a liquid is used in a car braking system. 1 mark

b The diagram below shows a small syringe connected to a largerone in a simple hydraulic system. Use the information in the diagramto calculate the force that will be applied to the large syringe plunger. 2 marks

c Explain why pumping up a tyre increases the pressure of the gasinside the tyre. 2 marks

5 Look at the diagram showing a beam balance.

a Explain, in terms of the principle of moments, why the beamis balanced. 2 marks

b A force of 25 N acts on a lever at a distance of 2 m from the pivot.

Calculate the size of the moment. 2 marks

c What force would be needed to make the beam below balance? 2 marks


force = 5 N force

1 cm2

(0.0001 m2)5 cm2

(0.0005 m2)

50 000 N/m2

left right

2 m

25 N

2 m0.5 mleft right

? 10 N


LEnd of unit test

RedPressure and moments (continued)

6 Ceri is experimenting with a balanced beam. It has two sliding masseson it. Ceri finds that if she moves the mass on the left side of the beam,the beam tips unless she moves the right hand mass to make it balance again.

Ceri makes a resultstable, and records thedistance between eachmass and the pivot asshe gets the beam tobalance.

Ceri makes aprediction that thereis a rule about balancedbeams. It is that the mass on one side of the pivot times itsdistance from the pivot is equal to the mass on the other sideof the pivot times its distance from the pivot.

Ceri removed the right sliding mass from the beam and replaced it withone that had twice the mass.

a i What did Ceri predict about how her results from her firstexperiment might change? 1 mark

ii Complete Ceri’sresults table with the results you would expect her to get. 1 mark

iii What could Ceri dowith her results sothat any patternsare easier to see? 1 mark

b i How could Ceri improve her experiment so that she could beconfident that her prediction was correct? 1 mark

ii What could Ceri do to her results table so that her data clearlyshows that her prediction was correct? 1 mark


left mass right masspivot

Distance between left Distance between right mass and pivot (cm) mass and pivot (cm)

6 6

15 14

17 17

25 25

Distance between left Distance between right mass and pivot (cm) mass and pivot (cm)

6

7

11

3


LEnd of unit test

mark schemePressure and moments


Green (NC Tier 3–6)Question Answer Mark Level

1 a 1 3

b Clockwise 1 3

2 a Shoulders 1 4

b Arms 1 4

c She uses her arms to counterbalance her weight. 1 5

3 B, C 2 4

4 a C or long-handled screwdriver. 1 5

b It will give the largest turning effect. 1 6Accept: it has the longest lever.

5 a A 1 4

b C 1 4

c This side has the largest area to spread the force. 1 5

6 a C 1 5

b Reduce the number of particles. 1 5Make the container larger. 1 5Accept: reduce the temperature.

7 a The snowboarder. 1 5

b They have the same weight 1 6but the snowboard has a bigger area. 1 6

8 Liquids can’t be squashed or liquids can transmit pressure. 1 6Gases can be squashed or gases can’t transmit pressure. 1 6

9 a Distance of the mass from the pivot. 1 4

b i The distances of the masses from the pivot are the 1 5same on each side.

ii The second pair of results are not identical. 1 5

c i The distance between the left mass and the pivot 1 6would be half that of the right mass (or the rightwould be double the left).

ii 12, 14, 22, 6. 1 6

pivot

Scores in the range of: NC Level

4–6 3

7–11 4

12–16 5

17–25 6


LEnd of unit test

mark schemePressure and moments


Red (NC Tier 5–7*)Question Answer Mark Level

1 a C or long-handled screwdriver. 1 5

b It will give the largest turning effect. Accept: it has the longest lever. 1 6

c The size of the force. 1 6

2 a A, D 1, 1 5

b She uses her arms to counterbalance her weight. 1 5

3 a It has largest area over which to spread the force. 1 5

b Pressure = force/area = 480 N/12 m2 = 40 N/m2 2 7One mark for correct equation and correct substitution but incorrect calculation; one mark for correct equationand incorrect substitution but correct calculation;two marks for correct answer with no working shown.

4 a Liquids can’t be squashed or can transmit pressure. 1 6

b Force = pressure × area = 50 000 × 0.0005 = 25 N 2 7One mark for correct equation and correct substitutionbut incorrect calculation; one mark for correct equationand incorrect substitution but correct calculation;two marks for correct answer with no working shown.

c There are more gas particles; so more collisions happen. 2 6

5 a Moments clockwise = moments anti-clockwiseAccept: force × distance gives the same moment on both sides, or similar. 2 6

b Moment = force × distance = 25 N × 2 m = 50 Nm 2 7One mark for correct equation and correct substitutionbut incorrect calculation; one mark for correct equationand incorrect substitution but correct calculation;two marks for correct answer with no working shown.

c Moment on right = 10 N × 2 m = 20 Nm 2 7*Force = moment/distance = 20 Nm/0.5 m = 40 NOne mark for correct equation and correct substitutionbut incorrect calculation; one mark for correct equationand incorrect substitution but correct calculation;two marks for correct answer with no working shown.

6 a i The distance between the left mass and the pivot would be half 1 6that of the right mass (or the right would be double the left).

ii 12, 14, 22, 6 1 6iii Put the results in order/have more results. 1 6

b i Repeat the experiment with more distances from the pivotand use other masses. 1 7

ii Add a column to each side showing the mass times the distancefrom the pivot. 1 7

Scores in the range of: NC Level

5–9 5

10–14 6

15–18 7

19–25 7*


L Pupil checklistPressure and moments


Learning outcomes I can do I can do I need to this very this quite do more well well work on this

I know that pressure depends on force and area.

I can use the equation pressure = force/area.

I can describe effects of high and low pressure.

I can describe some effects of pressure in liquids.

I understand how pressure in liquids and gases can be explained in terms of particles.

I understand that pressure increaseswith depth due to the weight of the substance above.

I understand that pressure increases withforce and decreases with area.

I can describe some effects of pressure in gases.

I can name a lever and a pivot.

I can describe how using a longer lever makes a job easier.

I can identify levers and pivots in the human body.

I can identify levers and pivots in machines.

I can use a beam balance.

I can describe how an object can be balanced.

I understand that the turning effect of a force is its moment.

I can plan and carry out an investigation using weights and a beam balance to find out about balance.

I can use the equation moment = force × distance from the pivot.

Pupil-Checklist.qxd 17-Jun-04 8:00 PM Page 12

L GlossaryPressure and moments


Word

air pressure

anticlockwise

clockwise

compress R

counterbalance

cylinder

equilibrium

exert

hydraulic machine

lever

load R

magnify R

moment

newtons per squaremetre, N/m2 R

pascal R

piston

pivot

pneumatic machine

pressure

principal of moments R

transmit R

turning effect

water pressure

Definition

The effect of a force spread out over an area.

When you exert pressure on something, you apply a force to it.

The unit by which pressure is measured. Also called a pascal. R

Another name for the unit newtons per square metre. R

To pass on from one place to another. R

To make something appear larger than it is. R

A machine that works by transferring pressure through a liquid.

Part of hydraulic and pneumatic machines. Pistons moveinside cylinders.

Part of a hydraulic or pneumatic machine that acts like aplunger, moving in and out of a cylinder.

The pressure in water. It is caused because water pushes onobjects from all sides as the water particles collide with theobject.

To squeeze into less space. When you compress a gas, theparticles move closer together and so the gas has a smallervolume. R

A machine that works by transferring pressure through acompressed gas.

The gas pressure caused when air particles all around us hitus and other surfaces.

The point around which a lever turns.

A force that is carried by a person or machine. The load isoften the weight of an object. R

A simple machine for lifting objects, that turns around a pivot.

When there is a force on an object and the force arrow is toone side of the pivot, the force has a turning effect on theobject.

Glossary.qxd 18-Jun-04 11:33 AM Page 13

L GlossaryPressure and moments (continued)


Definition

Moving in a curve in the opposite direction to the hands of aclock.

Moving in a curve in the same direction as the hands of aclock.

The turning effect of a force around a pivot. The moment ofa force depends on the size of the force and its distance fromthe pivot.

This states that when two moments are balanced, the sum ofthe anticlockwise moments equals the sum of the clockwisemoments. R

A weight used to balance another force, that stops something falling over.

When the forces on an object are balanced, it is inequilibrium.

Glossary.qxd 18-Jun-04 11:33 AM Page 14

L Key wordsPressure and moments

air pressure

anticlockwise

clockwise

compress R

counterbalance

cylinder

equilibrium

exert

hydraulic machine

lever

load R

magnify R

moment

newtons per square metre, N/m2 R

pascal R

piston

pivot

pneumatic machine

pressure


transmit R

turning effect

water pressure

Sheet 1 of 1

Sheet 1 of 1


Key wordsL Pressure and moments

air pressure

anticlockwise

clockwise

compress R

counterbalance

cylinder

equilibrium

exert

hydraulic machine

lever

load R

magnify R

moment

newtons per square metre, N/m2 R

pascal R

piston

pivot

pneumatic machine

pressure


transmit R

turning effect

water pressure


Keywords.qxd 18-Jun-04 11:35 AM Page 12


L Book answersPressure and moments

L1 Under pressureGreena The pressure at the sharp end is very high.b Camels’ feet are large and flat. The contact area

between the camel and the sand is large. Thismeans the pressure is quite low, so the cameldoes not sink into the sand.

c When the knife is blunt the cutting edge isflattened and has a large area. This causessmaller pressure from the blade so it will not cutvery well.

d The pressure will increase if the area decreases.e The woman with stiletto heels exerts higher

pressure. The heels have a very small area so herpressure is high. The baby elephant has widefeet. Its weight is spread over a large area so thepressure is low.

1 If you wear snowshoes ... your weight is spreadover a larger area than your feet.If you wear stiletto heels ... your weight is spreadover a smaller area than your feet.If you wear trainers ... your weight is spread overthe same area as your feet.

2 The person lying flat on the ice would be morelikely to reach the child. That person’s weightwas spread over a large area. The person walkingwould be more likely to crack through the icesince the shoes would have a smaller areacausing higher pressure on the ice.

3 They have large feet so that the pressure fromtheir feet on the mudflats is small and theydon’t sink into the mud.

4 Tractors sometimes travel through muddy fields.Their large wide tyres spread their weight outover a large area. This makes the pressure on themud less and they not likely to sink into themud. A plough is like a knife. It needs to besharp so that it has a small area to push into thesoil. The small area presents a large pressure andthe soil is more easily cut through.

5 Lying flat on a bed of nails spreads your weightout over a large area. This makes the pressuresmall at any one point. It would be even betterif the nails were slightly blunted as this wouldincrease the total area of the nail much moreand reduce the pressure greatly.

Reda Karl’s boots do not spread his weight over a large

area. The pressure under his boots is high andhe sinks into the snow.

b Camels’ feet are large and flat. The contact areabetween the camel and the sand is large. Thismeans the pressure is quite low, so the cameldoes not sink into the sand.

c The area of contact between the blade of a sharpknife and the object it is cutting is very small.This means the pressure is very high and the

blade will cut quite well. When the blade isblunt, it is flat rather than sharp, and it has alarge area, so the force of cutting is spread outover a larger area. Less pressure is produced andthe knife doesn’t cut the object so well.

d 3.75N/m2. The pressure has increased.e The woman’s pressure is

600 N ÷ 0.005 m2 = 120 000 N/m2.The elephant’s pressure is 60000N ÷ 0.8 m2 = 75 000N/m2.The woman exerts the higher pressure.

f 1.6N1 Force Area Pressure

30 N 10 m2 3N/m2

40 N 0.5 m2 80 N/m2

10 N 2 m2 5 N/m2

8 N 4 m2 2 N/m2

20 N 40 m2 0.5 N/m2

2 The rescuer lay flat on the ice so that his weightwould be spread over a larger area putting lesspressure on the ice than if he had walked on it.

3 a The pointed end of a pin has a very smallarea and the force will produce a very largepressure and puncture your skin. The head ofthe pin has a large area which causes a smallpressure from the same force and does noharm to your skin.

b Tractors sometimes travel through muddyfields. Their large wide tyres spread theirweight out over a large area. This makes thepressure on the mud less and they are notlikely to sink into the mud. A plough is like aknife. It needs to be sharp and thin so that ithas a small area to push into the soil. Thesmall area presents a large pressure and thesoil is more easily cut through.

c Stiletto heels have a very small area and theweight of a woman will produce enoughpressure on the floor to damage it.

4 a 40 000N/m2

b 20 000 N/m2

c The pressure increases because the area of histoes is less than the area of his shoes.

L2 Taking the plungeGreena No. The particles are already touching each

other.b biggerc It multiplies it to become a larger output force.d A car lift, braking system in a car, any other

correct answer.1 Hydraulic system – uses pressure in liquids,

which is the same in all directions.Water pressure – the pressure water has becauseof its own weight.

Book Answers.qxd 18-Jun-04 12:44 PM Page 31


L Book answersPressure and moments (continued)

Liquid – cannot be squashed because theparticles are already touching.Piston – the force on it depends on the pressureand its area.

2 Individual answers.3 The output piston.4 The weight of the water above you makes more

and more pressure on your body the deeper you go.

Reda The particles in a liquid are touching each other.

There is not enough space for any of theparticles to move into. So you cannot squash aliquid into any smaller volume.

b The larger plunger has an area 10 times the areaof the smaller plunger. The larger plunger has aforce 10 times the force on the smaller plunger.

c The shell of the submarine has to be very strongto withstand the tremendous water pressureit encounters when diving deep into the sea.

1 Input Area Pressure Output Areapiston in m2 in system piston in m2

Force in N/m2 Forcein N in N10 2 5 20 410 0.1 100 50 0.530 0.2 150 300 2

2 500 N3 a 50 N

b 50 Nc 200 N

4 Individual answers.5 The deeper you go in a pool, the heavier the

weight of water there is over you, pushing downon you. If you go too deep you can have enoughpressure to damage your ears.

L3 Pressure in the airGreena It squashes them closer together.b The pressure increases.c upd lower1 Air pressure – caused by the weight of air above you.

Pneumatic machines – machines that use asudden expansion of squashed gas.Volume of a gas – space taken up by gas particles.

2 decreasing3 Individual answers.4 The piston in the pneumatic drill is pushed

quickly into its cylinder, squashing the gas. Theother end of the cylinder has a moveable wallattached to a chisel. When the pressure insidethe piston gets high enough, the opposite wall ofthe cylinder moves out carrying the chisel whichhits the pavement. A strong spring then pulls thewall and chisel back into its original position and

the piston squashes the air again and the processis repeated over and over very quickly.

Reda The particles in a gas are spread out with lots of

space between them. When the gas is squashed,the particles are brought closer together and thevolume of the gas is decreased.

b The pressure inside the tyre increases more andmore as you pump. This happens because youare pushing more and more air particles into thetyre and the particles gets closer and closertogether, raising the pressure inside the tyre.

c If you pump too much air into a tyre or balloonthe strength of the rubber may not be enough towithstand the pressure put on it and it mightburst.

d The pressure inside the aircraft is higher thanthe pressure at the airport.

e 10 000 N1 decreasing2 a The pad is pushed up and down causing,

alternately, more and less pressure in theblocked pipe. The blockage is moved by thechanging pressure.

b The higher up a mountain you go, the less airthere is above you. The pressure from the airabove you decreases.

c Aeroplanes must keep the pressure inside thecabins about the same as at ground level. Thepressure outside the cabin during flight is verylow, so air must be pumped into the cabin.

3 a The particles are moving about randomly,knocking into each other and into the wallsof the can. Their speed is the same as thespeed of the air particles outside the can.

b When the can is heated, the particles moveabout much faster, knocking into the walls ofthe can with greater force, causing thepressure to increase.

c If the can is heated for a long time thepressure might get so high that the can willexplode.

4 Since the air pressure is low near the top of amountain, there are fewer particles of oxygenthat are breathed into the climber’s lungs witheach breath. Breathing becomes more rapid inorder to get enough oxygen.

5 Individual answers.

L4 Where’s the pivotGreena elbowb She is pushing near the hinge.c Her force is unbalanced.d The levers are the screwdriver and the crowbar.

The pivots are on the edge of the can andbetween the wooden beam.

e B




1 a false b falsec The shorter the lever, the bigger the force

that is needed to move an object.d The hinge of a door is its pivot.e Joints are examples of pivots.f Bones are examples of levers.

2


Reda balancedb

c Her weight becomes unbalanced.d Closer to the pivot.e The levers are the screwdriver and the crowbar.

The pivots are on the edge of the can andbetween the wooden beam.

1

2 A longer lever produces a greater turning force.3 Move the pivot or move the positions of the

people on the seesaw.4 The size of the force applied to the lever

and the distance between the pivot and theforce.

Force on lever

Pivot

Turningeffect

Force acting

ECOMIX

PivotForce acting on the wheelbarrow

Load

Force

Pivot

5 Design a flexible gripper to go round the item tobe unscrewed with long handles at the end sothat more turning force could be applied.


L5 Balancing actGreena Away from Mahir.b The distances are the same.c Mahir’sd Move closer to the end of the seesaw.1 Balanced system – two girls of the same weights

sit opposite each other on a seesaw, both thesame distance from the pivot.Unbalanced system – two boys of differentweights sit opposite each other on a seesaw,both the same distance from the pivot.Turning effect – gets bigger when the force actsfurther away from the pivot.

2 a They will both be the same distance from the pivot.

b The forces would be unbalanced. The end ofthe seesaw holding the heavier boy would godown.

3 James’

Reda They are both pushing the same distance

from the pivot.b 90Nmc The anticlockwise moment.d anticlockwise

1 a Their distances from the pivot are the same.b The forces would be unbalanced. The seesaw

would tip down on the side holding theheavier boy.

2 a The moment of a force is calculated bymultiplying the force times the distance ofthe force from the pivot.

b The seesaw will tip in an anticlockwisedirection.

3 Example Force in N Distance Moment offorce in Nm

A 10 1 m 10B 50 50 cm 25C 55 70 cm 38.5

4 a Anticlockwise: 350 N × 2 m = 700 Nm.Clockwise: 300 N × 1 m + 200 N × 2 m = 700 Nm.

b Yes. The seesaw will balance.

L6 Moments in lifeGreena anticlockwiseb You would have to move the remaining weight

further from the pivot.c The counterbalance.




d At all the places where there are joints; fingers,shoulders, elbows, wrists, neck, etc.

e Individual answers; lifting any heavy objectsfrom the floor.

1 Moment – turning effect of a force.Counterbalance – weight which stopssomething falling over.Pivot – point around which a lever turns.

2 more3 Individual answers.4 a Holding a long pole allows them to balance

the weight of their bodies with the turningforces on either end of the pole.

b With longer legs greater moments can beused.

Reda 1.5 m b 600 Nc By having a heavy counterbalance on one end

of the crane, the other end can be used to liftheavy weights.

d 400000N1 The moment downward caused by a long arm

(lever) is greater than the moment caused by ashort lever when held close to the body.

2 Individual answers.3 The weight on one side of the scale is placed at

the same distance as the pan on the other sidewhich holds the material being weighed.

4 2.5 m5 a At all the places where there are joints;

fingers, shoulders, elbows, wrists, neck, etc.b The arms.


L7 Getting balancedGreena The weight on the left-hand side of the beam,

the distance of the weight on the left-hand sidefrom the pivot, the weight on the right-handside of the beam and the distance of the weighton the right-hand side from the pivot.

b The moment on the left-hand side is equal tothe moment on the right-hand side.

c yes d yese Row C gives a combination that balances. The

moment on the left-hand side is equal to themoment on the right-hand side.

f E – 5 – 2 – 2 – 5g i 2 N ii 3 Nh Put Mary at 3m, Zahir at 2m or Mary and

Parveen at 2m.i Yes. If Joe moves to the 2m position, then the

seesaw will balance with Zahir at 1 m or Parveenat 3m.

1 If the question allows any number of weights tobe placed on the right-hand side, there would betoo many possible combinations to list here. So

we will confine ourselves to allowing only oneweight, of any value, to be placed on the right-hand side. Those possible answers to give a(clockwise) moment of 20 units on the right-handside would be: 5 N at position 4, 4 N at position 5,10 N at position 2 and 20 N at position 1.

2 Equilibrium means balanced. When somethingis in equilibrium, there are no movements. Allforces in a system are balanced by equal andopposite forces.

Reda The weight on the left-hand side of the beam,

the distance of the weight on the left-hand sidefrom the pivot, the weight on the right-handside of the beam and the distance of the weighton the right-hand side from the pivot.

b The beam will balance for rows A to D.c The distance times the weight on the left-hand

side equals the distance times the weight on theright-hand side.

d Left-hand side Right-hand side1 N in hole 5 2N in hole 2 1N in hole 1

1 N in hole 8 1N in hole 4 2N in hole 2

3 N in hole 7 7N in hole 3 no more

weights

2 N in hole 5 3N in hole 2 4N in hole 3 3N in hole 1

1 N in hole 7 4N in hole 5 5N in hole 5 2N in hole 1

6 N in hole 8 2N in hole 4 8N in hole 7 no more

weights

3N in hole 3 2N in hole 1 2N in hole 2

1N in hole 3

e i bigger ii smallerf For i, output force is 20 N. For ii, output area is

4 cm2.1 There are too many possible combinations of

the 18 weights and two 1 N hangers to list here. Individual answers must be scrutinised.Some possible combinations would be, on theright-hand side hang:both hangers on position 1 with 9 weights oneach hanger, hanger and 17 weights on position 1 and hangeronly on position 2, hanger and 15 weights on position 1 and hangerand 1 weight on position 2, hanger and 13 weights on position 1 and hangerand 2 weights on position 2, hanger and 13 weights on position 1 and hanger and 1 weight on position 3, hanger and 11 weights on position1 and hangerand 3 weights on position 2, hanger and 11 weights on position 1 and hangerand 1 weight on position 4, etc.

2 Equilibrium means balanced. When somethingis in equilibrium, there are no movements. Allforces in a system are balanced by equal andopposite forces. A level seesaw, a horizontalbeam balance, etc.


xxl pressure and moments unit guide - physicslocker...the concept described here where the forces...

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