7k forces and their effects

8/13/2019 7K Forces and Their Effects

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OUP: To be used solely in purchasers school or college

7K Forces and their effects

Identifying forces

Friction

Weight

Forces summary

7K Forces

and their effects


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Identifying forces



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What is a force and what does it do?

7K Identifying forces - What is a force?

A force is

You cannot see a force.

But you can feela force and see the effectof the force.

Forces make things happen or stop them from happening.

Name 5 ways in which you have used a force today.


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Forces can effect things in 3 ways. Can you name them?

7K Identifying forcesEffects of a force

Effect 3. A force can change

the directionof an object.


the speedof an object,

making it faster or slower.


the shapeof an object.


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7K Forces - Find the force

In each picture, identify the main force and describe its effect.

Click on the

picture to find the force


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7K Forces

Friction

7K F i ti Wh t i f i ti ?


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7K FrictionWhat is friction?

Friction occurs when any two surfaces move against

each other and tries to stop the movement.

Heatis generated as a result of friction.

Which type of surface generates more friction,

a roughsurface or a smoothsurface?

Put your palms together and rub hard. What happens?

You are creating the force called.

7K F i ti T k th h ith th th



7K Friction Take the rough with the smooth

7K F i ti Th t d d f



The friction of the tyres on

the road opposes

movement of the car.

The friction of air against the body of the

car also opposes the cars movement.

This type of friction is called

air resistance.

7K FrictionThrust and drag forces

What forces are acting on a racing car travelling at a

constant speed?

Drag forcesoppose the thrust forceand slow the car.

Where are these frictional forces?

drag

A thrust forcemakes the car moveforward.

Where does this force come from?

thrust

7K F i ti Th t d d f



What happens to the speed of the car when thethrust and drag forces are unbalanced?

7K FrictionThrust and drag forces

When the thrust and drag forces are balanced, the car

travels at a constant speed.

drag thrust

7K Friction High or lo ?



7K FrictionHigh or low?

7K F d th i ff t



Weight


7K Weight What is gravity?


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7K WeightWhat is gravity?

Why doesnt

water come out ofthe tap sideways?

Why does rain always

fal l downwardstowards the Earth?

Why dont people on the

other side of the Earth

fall off into ou ter space?

7K Weight What is gravity?


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7K WeightWhat is gravity?

The answer to all these questions is the force called

7K Weight What is weight?


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The pulling force of gravity always acts towards the

centre of the Earth, wherever you are on the planet.



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Why is weight different to mass?

Weight is a force and is measured in Newtons.

The effect of the force of gravity on an object is called

the objects

7K Weight Balanced forces


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7K Weight - Balanced forces

The girls weight due to the

force of gravity is pulling her

mass down on the chair.

An upwards forceis

produced by the chair in the

opposite direction to gravity.

The girl below is not moving. Are there any forces acting on her?

The girl does not move because these forces are balanced.

What does this tell you about the size of these forces?

7K Weight Changes in weight


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What happens to weight and mass when gravity changes?

Gravity changes depending on where you are in the Universe.

Our friendly alien Ms. R. Nerg will help you find out more

7K WeightChanges in weight



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On Earth, a

mass of 1 kg

has a weight

of 10 N.

My mass is

42 kg.

What is myweight on

Earth?



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The force of

gravity on the

Moon is

6 times lessthan on Earth.

My mass is

still 42 kg.

What is myweight on the

Moon?



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In outer

space, far

away from

any planets or

stars, there is

no gravity

pulling on me.

My weight in

outer space

is 0 N.What is my

mass in

outer space?

7K Weight Force of water


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Have you ever noticed how difficult it is to push an

inflatable under water?

How does upthrust help things float?

Thats because the water exerts an upwards force on

the inflatable.The upwardforce that acts on things in a liquid iscalled

7K Weight Force of water

7K Weight Why do things float?


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What does this tell you about the forces acting on it?

The floating rubber duck is not moving.

What forces are acting on the rubber duck as it floats?

7K Weight Why do things float?

Weightof the duck due to theforce of gravity

pulls downwards.

Upthrustof water pushes

upwards against the weight of

the duck.



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Forces summary


7K Forces summary Feel the force!


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2. The units that forces are measured in are called

a) metres.

b) newts.

c) Newtons.

1.Feel the force is a well-known saying from which

famous film?a) Star Wars.

b) Star Trek.

c) Stars in Your Eyes.



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3. Gravity and magnetism are examples of

a) contact forces.

b) non-contact forces.

c) police forces.

4. The force that occurs when two surfaces move against

each other is called

a) Fred.

b) fiction.

c) friction.




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5. In icy weather roads are covered with sand. How does the

sand effect the amount of friction between car tyres and

the road?a) Reduces friction.

b) Increases friction.

c) Has no effect.6. A dog being taken for a walk is pulling on the lead held

by its owner. The pulling force of the dog increases.

What happens to the speed of its owner?

a) Speeds up.

b) Slows down.

c) Changes direction.


7K Forces summaryFeel the force!


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7. The upwards force that slows down a sky diver as

they fall through the air is called

a) weight.

b) air conditioning.

c) air resistance.

8. The pulling force of the Earths gravity always

acts towards the centre of

a) the Moon.b) the Earth.

c) the Sun.

o ces su a y Feel the force!



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9. A cyclist is travelling at a constant speed.

The balanced pair of forces acting on the cyclist are

a) thrust and weight.

b) thrust and drag.

c) thrust and upthrust.

10. A computer on a desk does not move because

there are

a) no forces acting on it.b) unbalanced forces acting on it.

c) balanced forces acting on it.

y



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11.An astronaut drops a 1 kg bar of chocolate in outer space.

What is the weight of the bar of chocolate?

a) 10 N.

b) 1 N.

c) 0 N.

12.A spacecraft has a mass of 9000 kg on Earth.

What would its weight be on the Moon?

a) 1500 N.b) 9000 N.

c) 54 000 N.

y

7k forces and their effects

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