Friction is a force that slows the motion of two surfaces when they move across each other. An engine has many moving parts. If they rub against each other, creating friction, the efficiency of the engine is affected. The friction creates heat and the engine needs more energy to work. The parts also wear down as they come into contact. To reduce the friction in an engine, a lubricant, such as oil, is put between the moving parts.
There are also times when friction is useful. For example, if there were no friction between our feet and the ground, we would fall over. This can happen when a floor is polished or there is ice on the ground. There is less friction between our feet and these surfaces, so we easily slip.
The grooves on a tyre help to push water on the surface of the road out of the way. This means that there is more friction between the tyre and the road, preventing the car from skidding.
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