Friction: A Force That Slows Things Down

Friction is a force that appears when two surfaces rub against each other. It acts against movement, so it slows moving things down. Rubbing surfaces can also produce heat.

How much friction you get depends on the surfaces:

• Rough surfaces (a tar road, a rubber sole) give a lot of friction — good grip.
• Smooth or slippery surfaces (wet tiles, ice, polished glass) give little friction — things slide easily.

Friction is often useful: the rough tread on a minibus taxi's tyres grips the road, shoe soles stop you slipping, and brakes use friction to stop a bicycle.