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7K Forces and their effects

Identifying forces

Friction

Weight

Forces summary

7K Forces and their effects

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Identifying forces

7K Forces and their effects

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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 feel a force and see the effect of 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 forces – Effects of a force

Effect 3. A force can change the direction of an object.

Effect 2. A force can change the speed of an object, making it faster or slower.

Effect 1. A force can change the shape of 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

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7K Friction – What is friction?

Friction occurs when any two surfaces move against each other and tries to stop the movement.

Heat is generated as a result of friction.

Which type of surface generates more friction,a rough surface or a smooth surface?

Put your palms together and rub hard. What happens?

You are creating the force called .

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7K Friction – Take the rough with the smooth

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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 car’s movement.

This type of friction is called air resistance.

 7K Friction – Thrust and drag forces

What forces are acting on a racing car travelling at a constant speed?

Drag forces oppose the thrust forceand slow the car.

Where are these frictional forces?

drag

A thrust force makes the car move forward.

Where does this force come from?

thrust

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

 7K Friction – Thrust and drag forces

When the thrust and drag forces are balanced, the car travels at a constant speed.

drag thrust

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7K Friction – High or low?

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Weight

7K Forces and their effects

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7K Weight – What is gravity?

Why doesn’t water come out ofthe tap sideways?

Why does rain always fall downwards

towards the Earth?

Why don’t people on the other side of the Earth

fall off into outer space?

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7K Weight – What is gravity?

The answer to all these questions is the force called…

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7K Weight – What is weight?

The pulling force of gravity always acts towards the centre of the Earth, wherever you are on the planet.

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7K Weight – What is weight?

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 object’s…

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7K Weight - Balanced forces

The girl’s weight due to the force of gravity is pulling her

mass down on the chair.

An upwards force is 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?

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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 Weight – Changes in weight

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7K Weight – Changes in weight

On Earth, a mass of 1 kg has a weight

of 10 N.

My mass is 42 kg.

What is my weight on

Earth?

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7K Weight – Changes in weight

The force of gravity on the

Moon is 6 times less

than on Earth.

My mass is still 42 kg. What is my

weight on the Moon?

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7K Weight – Changes in weight

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?

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Have you ever noticed how difficult it is to push an inflatable under water?   

How does upthrust help things float?

That’s because the water exerts an upwards force on the inflatable.  The upward force that acts on things in a liquid is called…

7K Weight – Force of water

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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?

Weight of the duck due to theforce of gravity

pulls downwards.

Upthrust of water pushes upwards against the weight of

the duck.

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Forces summary

7K Forces and their effects

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7K Forces summary – “Feel the force!”

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.

7K Forces summary – “Feel the force!”

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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 summary – “Feel 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 Earth’s gravity always acts towards the centre of…

a) the Moon.

b) the Earth.

c) the Sun.

7K Forces summary – “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.

7K Forces summary – “Feel the force!”

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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.

7K Forces summary – “Feel the force!”