Friction

Why do you slip on a wet floor?

A force that slows

Friction is a force between two surfaces that rub together. It always works against movement. It slows moving things down and can stop them.

Rough and smooth

Rough surfaces make more friction than smooth ones. A ball rolls further on smooth tiles than on a rough carpet or grass. Wet and icy floors have little friction, so we slide and slip.

Useful friction

We need friction! The patterns on shoe soles and tyres grip the ground. Bicycle brakes use friction to slow the wheels.

Without friction, you could not walk – your feet would slip. Knots in ropes would come undone, and nails would slide out of wood.

Reducing friction

Sometimes friction is a nuisance. It wears things out and makes them hot. We put oil or grease on machines and bicycle chains. This lubricant reduces friction.

What I learnt

I know that friction is a force that slows things down.
I know that rough surfaces make more friction.
I can give examples of useful and unhelpful friction.