In order to stop a fast-moving motor vehicle within seconds, the vehicle's brakes have to be able to generate a greater force than the engine can. The braking power is friction, caused between surfaces consisting of a complete area which is approximately the size of your hands.
The power of brakes is so mighty because the brake shoe or pad and the brake drum or disc, are thrust together simultaneously with a great force. If the brakes are unassisted, the push given by the driver's foot is amplified with the help of hydraulics within the braking system. There are two main types of brake, the drum brake and the disc brake.
Within drum brakes, the application of friction is placed upon the inside of a rotating drum by the brake shoes. Because this causes a lot of heat to build up it reduces the friction, and therefore gives less power to stop. For this reason, drum brakes are usually fixed to the rear wheels of a motor vehicle. The handbrake gives an additional stopping power to the back wheels, as it is frequently fitted to operate the rear brakes. It can do this by means of a mechanical linkage.
In the disc brake, the friction from the brakes is directed to each side of the spinning disc. This allows an intense heat to be produced without affecting the performance, so giving enormous stopping force. The heat generated is withdrawn by an air flow over the disc. Disc brakes can usually be found on the front wheels of a motor vehicle (although sometimes used on all wheels) because more braking power is needed there.
