<P> The disc brake is a device for slowing or stopping the rotation of a road wheel . A brake disc (or rotor in U.S. English), usually made of cast iron or ceramic, is connected to the wheel or the axle . To stop the wheel, friction material in the form of brake pads (mounted in a device called a brake caliper) is forced mechanically, hydraulically, pneumatically or electromagnetically against both sides of the disc . Friction causes the disc and attached wheel to slow or stop . </P> <P> Pumping brakes are often used where a pump is already part of the machinery . For example, an internal - combustion piston motor can have the fuel supply stopped, and then internal pumping losses of the engine create some braking . Some engines use a valve override called a Jake brake to greatly increase pumping losses . Pumping brakes can dump energy as heat, or can be regenerative brakes that recharge a pressure reservoir called a hydraulic accumulator . </P> <P> Electromagnetic brakes are likewise often used where an electric motor is already part of the machinery . For example, many hybrid gasoline / electric vehicles use the electric motor as a generator to charge electric batteries and also as a regenerative brake . Some diesel / electric railroad locomotives use the electric motors to generate electricity which is then sent to a resistor bank and dumped as heat . Some vehicles, such as some transit buses, do not already have an electric motor but use a secondary "retarder" brake that is effectively a generator with an internal short - circuit . Related types of such a brake are eddy current brakes, and electro - mechanical brakes (which actually are magnetically driven friction brakes, but nowadays are often just called "electromagnetic brakes" as well). </P> <P> Electromagnetic brakes slow an object through electromagnetic induction, which creates resistance and in turn either heat or electricity . Friction brakes apply pressure on two separate objects to slow the vehicle in a controlled manner . </P>

How can you use vehicle's engine as a brake