A machine element for applying a force to a moving surface to slow it down or bring it to rest in a controlled manner. In doing so, it converts the kinetic energy of motion into heat which is dissipated into the atmosphere. Brakes are used in motor vehicles, trains, airplanes, elevators, and other machines. Most brakes are of a friction type in which a fixed surface is brought into contact with a moving part that is to be slowed or stopped. Brakes in general connect a moving and a stationary body, whereas clutches and couplings usually connect two moving bodies.