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What is friction?

Grips on the soles of running shoes stop you slipping.Grips on the soles of running shoes stop you slipping.Friction is a force that tries to stop things moving. It is produced when two surfaces rub together. Rough surfaces produce more friction than smooth ones. Friction can cause problems, such as making machines wear out. But friction can also be helpful. Friction caused by the grips on your shoes, for example, stops you slipping over. Water and air can also both cause friction.

Reducing or increasing friction

Cyclist. Insets show brakes (top) and gears (above).Cyclist. Insets show brakes (top) and gears (above).

This cyclist’s “streamlined" helmet and smooth lycra clothing help to reduce friction, enabling him to move faster. The cogs and chains on a bike are coated in slippery oil to reduce friction. This keeps them running smoothly. 

To slow down, the cyclist squeezes the brakes, which grip the wheel rims, causing friction. The tread on a bicycle’s tyres increase friction. This allows the tyres to grip the road.

Our fingerprints give our fingers grip. This is because the tiny ridges in the skin provide friction. Fingerprints allows us to hold objects more easily. They might slip out of our hands if we had smooth fingertips. Apes (and koalas) also have fingerprints.

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