Brakes are mechanical devices that inhibit motion by applying artificial frictional resistance to moving machine parts to retard or stop their motion. There are several types of brakes including disk brakes, drum brakes, vacuum brakes, air brakes, hydraulic brakes, and railway brakes. A single block or shoe brake consists of a block or shoe made of softer material than the rim of a revolving brake wheel drum that is pressed against the rim to slow or stop rotation.