Brakes slow a car down by making extra friction, which is in the opposite direction to the movement of the car. The acceleration is .

The greater the speed, the bigger the force that is needed to stop a car in the same distance. If you are driving at 50 km/h, it only needs a light force on the pedal to stop the car in 100 m. If you are driving at 100 km/h it would need a much bigger braking force to stop the car within 100 m.

When you have to stop really quickly, for example a child runs out in the road in front of you, a significant proportion of the stopping distance is taken up with the " distance". There is a reaction time while you see the emergency, realise there is an emergency, and then put your foot on the brake. During this time, the car is still travelling at the speed.

The braking distance will increase if:

- the car is in poor condition, especially if the are worn down;
- the road is or greasy.

If there is ice, there is very little , and braking has to be done very carefully indeed. Ice is one of the slipperiest substances known.

Some people try to drive after have several in the pub, or worse still, having taken drugs.

Why is it so dangerous to drive while drunk? Although people have a sense of well-being, alcohol has a depressing effect on the brain. This results in:

- loss of inhibition, making people show off by driving , or more aggressively;
- loss of coordination;
- appreciation of dangerous situations;
- much slower time when an emergency arises.