CHAPTER 3

FORCES AND PRESSURE

3.1 Understanding pressure ( ……… / 8 x 100 % = ……………

% )

A student is able to:

Define pressure and state that

Describe applications of pressure

Solve problems involving pressure

1. What is meant by pressure?

(1)...................................................................................................................................

.

2. Choose ( √ ) the examples that apply the concept of pressure? (2-5)

( ) Dispensing toothpaste ( ) Hammering a nail

( ) Using a wider seat belt ( ) Cutting meat with a knife

( ) Ship staying afloat ( ) Aerofoil shaped aeroplane

3.

A girl is going to take a walk on a soggy field. There are two types of shoes as

shown in diagram 3.

Which type of shoes should she wear?

(6)...................................................................................................................................

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4. Diagram shows a 2 kg cuboid on a table.

Calculate the pressure exerted on the table by the cuboid. Tick (√) the correct

answer. (7)

Diagram 4

( ) 0.8 N m-2

( ) 50 N m-2

( ) 200 N m-2

( ) 500 N m-2

5. Diagram 5 shows a 5kg cuboid on a table in 3 different positions.

Circle the diagram in which the cuboid exerts the least pressure on the table. (8)

Diagram 5

2

0.4 m

0.1 m

3.2 Understanding pressure in liquids ( ……… / 8 x 100 % = ……………%

)

A student is able to:

relate depth to pressure in a liquid

relate density to pressure in a liquid

explain pressure in a liquid and state that P = h ρ g

describe applications of pressure in liquids.

1. What is the relationship between depth of liquid and pressure?

(1)............................................................................................................................

2. What is the relationship between density of liquid and pressure?

(2)..............................................................................................................................

3.

Diagram 3

Diagram 3 shows a container of oil.

Underline the correct answer

Point ( X , Y ) has the highest pressure? (3)

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4. The relationship of Pressure in liquid is, P =hρg

What is represented by h, ρ and g respectively?

h = (4) ..............................

ρ = (5) .............................

g = (6).............................

5. State one application of pressure in liquid.

(7)............................................................................................................................

6.

Diagram 6

Diagram 6 shows a glass full of alcohol.

What is the pressure at P? Tick (√) the correct answer. (8)

[ Density of alcohol = 800 kg m-3 ]

( ) 1600 Pa

( ) 16 000 Pa

( ) 160 000 Pa

( ) 1 600 000 Pa

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3.3 Understanding gas pressure and atmospheric pressure

( ……… / 15 x 100 % = ……………% )

A student is able to:

explain gas pressure

explain atmospheric pressure

describe applications of atmospheric pressure

1. A student wrote several statements to explain gas pressure.

However they were NOT in the correct order.

Rearrange the statements in the correct sequence to explain gas pressure.

[Write numbers 1, 2, 3 or 4 in the sequence column]

(1 – 4)

Sequence Statements

Collisions of gas particles in the container occur very frequently.

Gas is made up of tiny particles.

The collisions of gas particles on the wall of container give rise to gas

pressure

Gas particles move randomly with high speed.

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2.

Diagram 2

Diagram 2 shows a manometer connected to a gas tank.

Determine the gas pressure shown.[ Atmospheric pressure = 76 cm Hg] (5)

3.

Diagram 3

Diagram 3 shows a manometer. What will happen to the mercury column Y if X is

connected to a high pressure gas tank?

(6) ………………………………………………………………………………………..

4. Underline the correct answer.

(a) The ( weight , mass ) of air on the earth’s surface gives rise to the atmospheric

pressure. (7)

(b) A mountain terrain has a (8) ( higher , lower ) atmospheric pressure than at

the sea-side because the air at the mountain terrain is (9) ( thicker , thinner ).

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5. It is found that a Fortin barometer reads 74 cm Hg at a highland

whereas the reading is 76 cm Hg at the sea side.

Based on the statement, tick (√)

i. a correct inference (10)

ii. a correct hypothesis (11)

i ( ) The atmospheric pressure is influenced by the altitude

( ) The atmospheric pressure is influenced by the type of barometer

ii. ( ) The higher the altitude from sea level the lower the atmospheric pressure

( ) The lower the altitude from sea level the lower the atmospheric pressure

6. Fortin barometer X reads 74 cm whereas Fortin barometer Y reads 76 cmHg.

Which of the following statements correctly explain the difference in atmospheric

pressure in the terms of altitude?

Tick (√) at the correct statements. (12 – 13)

The Fortin barometer X measured the atmospheric pressure at lower altitude.

The Fortin barometer X measured the atmospheric pressure at higher altitude.

The Fortin barometer Y measured the atmospheric pressure at lower altitude.

The Fortin barometer Y measured the atmospheric pressure at higher altitude.

8. List two applications of atmospheric pressure.

i .

(14) .........................................................................................................................

ii.

(15) .........................................................................................................................

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3.4 Applying Pascal’s Principle ( ……… / 10 x 100 % = ……………

% )

A student is able to:

state Pascal’s principle.

Explain hydraulic system

Describe applications of Pascal’s principle.

Solve problems involving Pascal’s principle.

Instruction : Answer all questions in this section.

1. Pascal’s Principle states that

(1)………………………………………................................................................

…………………………………………………………………………………………..

2. Give 2 examples of the application of Pascal’s Principle

(2) …………………….…………. (3)……………………….......................

3. Diagram 3 shows a application of Pascal’s Principle.

Diagram 3

State the relationship between F1, F2, A1 and A2.

(4) ……………………………………………………………………………………

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4. Diagram 4 shows one application where pressure is transmitted

equally through an oil. Name of the system : (5)………………………..

Diagram 4

5. Diagram 5 shows toothpaste being squeezed out from the tube. The principle

that explains the situation below is (6)………………………………

Diagram 5

6. Diagram 6 shows a : (7)………………………..

Diagram 6

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7. Diagram 7 shows a simple hydraulic system. A1 and A2 are cross

section area of the piston. A1 = 5 cm2 and A2 = 10 cm2.

Diagram 7

(a). What is the minimum force F1 which can lift a load of 100 kg ?

(8)

…………………………………………………………………………………

(b). What will happen to the hydraulic jack if the force F1 is less than the value

found in 7(a)?

(9) …………………………………………………………………………………

(c). Give one reason for your answer

(10)

……………………………………………………………………………………

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3.5 Applying Archimedes’ Principle ( ……… / 26 x 100 % = ……………% )

A student is able to:

Explain buoyant force

Relate buoyant force to the weight of the liquid displaced

State Archimedes’ principle.

Describe applications of Archimedes principle

Solve problems involving Archimedes principle

1. Buoyant force is the (1) …………….. force acting on an object immersed in a

fluid.

2. Archimedes' Principle states that if an object is partially or fully immersed in a

fluid, it experiences a buoyant force equals to the (2) ……………….. of the fluid

displaced.

3. Give 2 examples of the application of Archimedes' Principle

(3) …………………………….., (4) ………….………………..

4. Diagram 5 shows a spring balance supporting a metal block K in three

situations.

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Diagram 5

(a) Compare the readings of the spring balance in Diagram 5A and Diagram 5B.

(5)

……………………………………………………………………………………

(b) The three forces that act on K when it is partially or totally immersed in

water are it’s weight (W), tension (T) and buoyant force (J). Mark the 3 forces

in diagram 5a or b. (6)

(c) Write down the relationship between the forces in (b).

(7)

…………………………………………………………………………………

(d). (i). What will happen to the spring balance reading in diagram 5C if the water

is replaced with salt solution?

(8)

……………………………………………………………………………………

(ii) Give one reason for your answer.

(9) …..

………………………………………………………..……………………

5. A submarine can sail on the surface or under the sea. Explain how a

submarine on the surface can submerge.

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a) The submarine has a (10)____________.

b) Water is (11)_________ in the ballast tank.

c) The submarine sinks when its (12) ___________ is more than that of the

water and its weight is equal/more than the (13)______________.

6. Diagram 7A and 7B show two different situations of a boat with the same load

in different waters.

Diagram 7

Compare the levels of the boats in diagram 7 and the volumes of water displaced by

the boat. Relating the mass of the boat with its load, the volume of water displaced

and the density of the water, deduce a relevant physics concept.

a) The boat (14) _________ more in the river than in the sea.

b) Sea water is (15) ___________ than river water.

c) The (16) _________ of the boat and its load is the same when it is in the

sea and in the river.

d) The boat floats because it is being balanced up by the (17) _____________.

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e) The buoyant force is equal to the weight of (18) _________________.

f) (19) _______water will be displaced when the density is lower.

The boat sinks more when the density is (20)__________.

7. Diagram 8A and B illustrate the working principle of a hydrometer. The depth

to which the test tube sinks depends on its surrounding liquid.

Diagram 8

Explain how you would design a hydrometer that can determine a wide range

of densities of liquid, using the idea of the working principle of hydrometer in

diagram 8A and diagram 8B. Draw a diagram that shows the design of your

hydrometer and in your explanation. Consider the following aspects:

- the stability of the hydrometer,

- the sensitivity of the hydrometer,

- the ability to measure a wide range of densities of liquids,

- the calibration of the hydrometer.

a) Draw a correct design of the hydrometer. (21)

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b) Put (22) ___________ ball bearings in the glass bulb, to ensure the

hydrometer is upright.

c) Use a (23) _________ stem, to have a bigger interval of the scale.

d) Use a suitable big bulb and a (24) ________ stem. So that the hydrometer

does not sink fully in low density liquid.

e) (25)__________ the hydrometer into a paraffin oil / alcohol to calibrate for

liquid of low density.

f) (26)__________ the hydrometer into a carbon tetrachloride solution to

calibrate for liquid of high density.

Learning Objective

3.6 Understanding Bernoulli’s principle. ( ……/ 28 x 100 % = ……………% )

Learning Outcomes

A student is able to:

State Bernoulli’s principle

Explain that resultant force exists due to a difference in fluid pressure

Describe applications of Bernoulli’s principle

Solve problems involving Bernoulli’s principle

1. Bernoulli's Principle states that the pressure exerted by a fluid (1) ……………

as its velocity increases.

2. Name 4 examples of application of the Bernoulli's Principle:

i (2)……………………..,ii (3).…….………………….,iii (4)……………….…..,

iv (5)………………………………….

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3. Diagram below shows a piece of paper hanging from a retort stand. When air

flows from the nozzle of an air pump, the paper changes its position as shown

in Diagram B.

Diagram 3

(a) Compare the position of the paper in Diagram 3A and Diagram 3B.

(6).……………………………………………………………………………………

(b) F is a force that causes the paper to change its position. In box X, on

Diagram B, indicate and label the direction of F that acts on the paper. (7)

(c) Explain how F is produced.

i (8)…………………………………………………………………………………

ii (9)

……………………………………………………………………………………

(d) (i) What happens to the paper in Diagram B when the air flows faster ?.

(10) ……….………………………………………………………………………

(ii). Give a reason for your answer in (d)(i).

(11).………………………………………………………………………………

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(e) Name the principle that causes the observation in Diagram B.

(12) .……………………………………………………………………………………

4. Diagram A below shows the situation of a sheet of paper before and when air is

blown. Diagram B shows the situation of canopy before the lorry moves and

when the lorry moves at high speed.

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Diagram 4

(a) Based on Diagram 4A and Diagram 4B :

(i) State two similarities for the situations in Diagram 4A and

Diagram 4B.

(13)

……………………………………………………………………………………

(14)

……………………………………………………………………………………

(ii) Compare the air pressure above and below the paper when air

is blown.

(15)

………………………………………………………………………………

(iii) Relate the speed of the air to the pressure of the air.

(16)

………………………………………………………………………………

(b) Name the principle involved in question (a)(iii).

(17) ………………………………………………………………………………

5. Diagram 5 shows an instrument used to measure the speed of air.

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Diagram 5

In Diagram 5A shown the level of coloured water in the U-tube is the same

before air flows.

(a) Compare the speeds of air at P and Q when air flows as in diagram B.

(18)

……………………………………………………………………………

(b) Mark the water level in the U-tube in Diagram B when air flows. (19)

6. Diagram 6 shows a cross-section of a wing of a moving aero plane.

The wing of the aeroplane experiences a lift force.

Diagram 6

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(a) Name the shape of the cross-section in Diagram 6.

(20)…………………………………………………………………………………

(b) Explain why the lift force acts on the wing of the aeroplane.

i (21)……………………………………………………………………………

ii (22)…………………………………………………………………………………

iii (23)…………………………………………………………………………………

7. Diagram 7 shows a model of an aeroplane.

Diagram 7

You are required to give some suggestions to design a aero plane which can

travel faster and is more stable.

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Using the knowledge on motion, forces and the properties of materials, explain

the suggestion based on the following aspects:

- the surface of the plane

- the shape of the plane

- material used for the plane

- position of the wing

- the size of the wing

a) (24)__________ surface. To reduce air friction between air plane and air.

b) (25)_____________ shape. To reduce air friction also.

c) (26)________________ material. To reduce the weight and easy to fly.

d) The wings are positioned higher up on the body so that the aeroplane is

(27)_________________ .

e) (28)___________ wings. To increase the uplift (force)..

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