# Friction

## Key Stage 2

### Meaning

Friction is a force that slows things down when two surfaces are touching each other.

Singular Noun: Friction
Plural Noun: Friction

Friction can only happen when two surfaces are touching so it is called a "Contact Force".
Friction depends on the texture of a surface.
The rougher a surface is, the more friction an object will experience when it is moving.
The smoother a surface is, the less friction an object will experience.
A surface could be described as high friction or low friction.
Sometimes a low friction surface is called "slippery".

### Experiments

Friction and Shoes

Good shoes are designed to have a high friction surface on the sole. Take off one of your shoes and look at the bottom of your shoe with a magnifying glass.

You might try to answer the following questions:

• Who has the slipperiest shoes and how do slippery shoes look different from shoes that are not slippery?
• When shoes get older, how does the bottom of the shoes look different and do shoes get more slippery or less slippery as they get old?

Friction of different surfaces

1. Take a flat piece of wood and attach spring to one end.
2. Pull the piece of wood by the spring along the carpet and measure how long the spring is as you drag it.
3. Repeat this by dragging it along a table and the tarmac outside.
4. Write down which surface made the spring go longest. That is the surface with most friction.

## Key Stage 3

### Meaning

Friction is a force that acts to slow an object down when two solid surfaces are in contact.

Friction is a force so it is measured in Newtons.
Friction is a contact force because it only exists when two surfaces are touching.
Friction occurs because two rough surfaces have bumps that fit together resisting them from sliding against each other.
 The two diagram shows two rough surfaces and two smooth surfaces. The friction between the rough surfaces is greater because there are more bumps in the way to prevent the surfaces sliding against each other.

### Examples

 Friction acts at the point where the bowling ball touches the ground. The force of friction acts to decelerate the bowling ball as it moves. Friction acts at the point that the tyres touch the ground. The force of friction can act to decelerate the car but can also be use to accelerate the car. If there was no friction the wheels would spin but the car would not accelerate.

## Key Stage 3

### Meaning

Friction is a force that acts prevent two surfaces from sliding over one another.

Friction is a force so it is measured in Newtons.
Friction is a contact force because it only exists when two surfaces are touching.
Friction occurs because two rough surfaces have bumps that fit together resisting them from sliding against each other.
 The two diagram shows two rough surfaces and two smooth surfaces. The friction between the rough surfaces is greater because there are more bumps in the way to prevent the surfaces sliding against each other.
Friction can act to decelerate an object sliding along a surface. However, it also allows objects with a driving force to accelerate by preventing a wheel from sliding against the surface.
The friction between two surfaces can be reduced with a lubricant which keeps the rough parts of two surfaces separated.
 The two diagram shows how rough surfaces can be separated by a lubricant reducing the friction between them.

### Energy Transfer

When two surfaces slide over one another work is done by friction to transfer energy from the kinetic energy store to the thermal energy store of the system.

### Examples

 Friction acts at the point where the bowling ball touches the ground. The force of friction acts to decelerate the bowling ball as it moves. Friction acts at the point that the tyres touch the ground. The force of friction can act to decelerate the car but can also be use to accelerate the car. If there was no friction the wheels would spin but the car would not accelerate.

### References

#### AQA

Friction, page 19, GCSE Physics, Hodder, AQA
Friction, pages 16, 53, 63, 67, GCSE Physics; The Revision Guide, CGP, AQA
Friction, pages 209, GCSE Combined Science Trilogy 2, Hodder, AQA
Friction, pages 26-7, 156, 148, 167, GCSE Physics; Student Book, Collins, AQA
Friction, pages 9, 14-15, 50, 117-118, 146-147, 149, GCSE Physics; Third Edition, Oxford University Press, AQA

#### Edexcel

Friction, page 132, GCSE Physics, Pearson Edexcel
Friction, page 374, GCSE Combined Science, Pearson Edexcel

#### OCR

Friction, 63, 66-67, Gateway GCSE Physics, Oxford, OCR
Friction, pages 163, 205, Gateway GCSE Combined Science; The Revision Guide, CGP, OCR
Friction, pages 26, 29, 85, Gateway GCSE Physics; The Revision Guide, CGP, OCR