An engine is a mechanical device that produces some form of output from a given input. When the purpose of an engine is to produce mechanical power from a fuel source it is referred to as a prime mover; alternatively, a motor is a device which produces mechanical power from other forms of energy (such as electricity, a flow of hydraulic fluid, or compressed air). An automobile makes use of several motors to start the car and drive the car's various pumps (fuel, power steering, etc) – but the power plant that propels the car is called an engine. The term 'motor' was originally used to distinguish the new internal combustion engine -powered vehicles from earlier vehicles powered by a steam engine (as in steam roller and motor roller).
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