Our life is pull of forces. We cannot see them but we can see how they affect things. Forces can change the shape of something, its speed, or the direction that it is moving in.
This is an example of friction.
Forces are either pushes or pulls. These pictures show some changes caused by forces. Many forces need to touch an object before they can affect it. These are called contact forces.
Friction is the force between two touching objects. It can slow things down or make things stand still. The friction between our clothes and a chair stops us from sliding off it. Walking would be very difficult without the frictions between our feet and the floor – we would slip and slide everywhere.
Friction can also wear things away. The brake pads on a bicycle eventually wear away, and so do car tyres. Parts of your clothes get thinner as friction wears them away.
Friction produces heat and noise. If a car engine runs without any oil in it, the large friction between the moving parts inside the engine causes it to overheat and stop working. Rusty door hinges squeak and make a door difficult to open.
We can increase friction by using certain materials. Rubber produces a lot of riction which is useful to use. The tyres of a Formula One racing car stop the car from sliding off the road as it speeds round a sharp bend. The rubber mat in a bath stops us from slipping.
We can reduce friction by making surfaces smooth. Skiers wax the bottom of their skis to make them very smooth. This reduces friction and allows them to ski faster.