### KS3 Physics

Energy
Motion and Forces
Waves
Electricity and Electromagnetism
Matter
Space Physics

# Frictional Forces

Frictional forces are formed when two objects move against each other. These are forces that move in opposite directions, making it harder for an object to move.

Frictional forces are greater on rigid surfaces than on smoother surfaces.

• Between car tyres and the road – this stops cars from skidding
• Between shoes and the floor – to stop us from slipping
• Between the brakes and the wheel of a car – to slow the car down

However, sometimes friction is not helpful:

• The friction between the chain of your bike and the axles causes a lot of noise and makes it difficult to pedal
• In a car, friction between moving engine parts can cause the engine’s temperature to rise and lead to wear and tear on the parts

## Examples of Friction

### Friction in our Homes

Holding Objects – Friction is required to hold onto any object. Without it, objects would slip from your hands.

Using an eraser – When you rub an eraser on paper, it overcomes the frictional force between the lead particles (from the pencil) and the paper.

### Friction Outdoors

Polishing rough surfaces – You can use sandpaper to smooth rough or sharp edges. Rough surfaces have more irregularities than smooth surfaces do. The rough and rigid surface of the sandpaper increases friction, which helps to eliminate the irregularities on rough surfaces, making them smoother.

Tug of War – In this game, two teams pull on a long rope. The friction between the players’ hands and the rope helps them maintain their grip.

### Friction in Nature

Forest fires – Trees can rub against each other due to high wind velocities. This builds up friction and heat, which can lead to forest fires.

Climbing trees – There are many animals that have sharp claws, hairy feet or both. These can be used to climb trees. For example, a strong friction exists between the animals’ claws and the tree’s rough surface.

Quizzes