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Forces and Motion

The Stopping Distance of a Car - Friction.

What Conditions affect the Stopping Distance of a Car?

The braking force that brings a car to a stop depends
on the friction between the brakes and the wheels
and the friction between the tyres and the road surface.

The total stopping distance = thinking distance + braking distance.

Changing the friction does not change the thinking distance
but the
braking distance is changed as the amount of friction changes.

How does Friction affect the Braking Distance of a Car?

When the brakes are applied the car loses kinetic energy
(it slows down). The kinetic energy which is lost is
transferred to the brakes and the wheels which both get hotter.
If the brakes are not seriously worn or malfunctioning,
then the friction between the brakes and the wheels
is very good because of modern brake design and materials.

The most important friction for stopping a car occurs between the
tyres and the road surface. If the road is wet or icy, then
the friction is reduced and the braking distance is increased.

If the brakes are applied with too much force the tyres
will slide on the road surface (called skidding).
On a wet road, the tread on the tyre makes water on
the surface of the road go up into the grooves
and then the water is thrown out sideways to get it out
from under the tyre. If the tread is not deep enough
the tyre can not remove surface water quickly enough
and the tyre will ride up on top of the water
and loose contact with the road (called aquaplaning).

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