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Physics and Car safety
Brakes

Brakes use physics to perform their job in a car and are very important in a collision because in order to stop in time the brakes must be in good working order.
 
There are a few aspects of physics that brakes deal with.One is force which is shown through a lever in the pedal. As your foot pushes down on the pedal providing a force the lever multiples this force. The reason the force is multiplied is because our foot can not provide enough of a force to stop a car so the lever system does this.
 
One side of the lever in the pedal is twice as long as the other. As our foot provides a small force to the longer side of the pedal the lever system allows the force to be multipled because the force before must be equal to the force after. Since the first side is double the length and a small force and the second side is half the length, the force must be double so the force before is equal to after.This greater force allows the brake to stop the car, sometimes avoiding a collision.

brake-leverage.gif
Source:http//auto.howstuffworks.com/brake.htm

Brakes also use hydraulics which involve physics because of the forces involved. A hydraulic system is similar to a lever system when physics is involved. In the hydraulic system the force is multiplied as is done in the lever system. In order for forces to be multipied the sizes of the pistons used must be different. If you apply a force to a smaller diameter piston and it connects to a larger diameter piston the force will be multiplied by the difference in area between the two pistons.
 
The amount of force needed to be placed on the brakes in order to stop the car depends on the surface the car is driving on. If the car is driving on a surface where more traction is available such as gravel compared to ice, then there will be less of a force needed to stop the car. The opposite is true for starting a car on each surface. There is a lot less force required to move a car tire along a  slippery surface then one with more friction involved. The reason for this is because a gravel road has a greater coefficent of friction then an icey road which means that there is more "stickiness" between the two objects.

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