An electric motor is an electric machine that converts electrical energy into mechanical energy. The reverse of this is the conversion of mechanical energy into electrical energy and is done by an electric generator, which has much in common with a motor.
Most electric motors operate through the interaction between the magnetic field of an electric motor and the winding currents to generate force. In certain applications, such as in regenerative braking with traction motors in the transportation industry, electric motors can also be used in reverse as generators to convert mechanical energy into electrical energy.
Electric motors, which are in applications as diverse as industrial fans, blowers and pumps, machine tools, electrical appliances, power tools and disk drives, can be powered by DC power sources, such as batteries, motor vehicles or rectifiers; by sources of alternating current (AC), such as from the grid, inverters or generators. Small engines can be found in electric watches. General purpose motors with highly standardized dimensions and characteristics provide mechanical power suitable for industrial use. The largest of the electric motors are used for vessel propulsion, compression piping and pumping storage applications with ratings reaching 100 megawatts. Electric motors can be classified by type of electric power source, internal construction, application, type of output of movement, etc.
Electric motors are used to produce linear or rotating force (torque), and must be distinguished from devices such as magnetic solenoids and loudspeakers that convert electricity into motion but do not generate usable mechanical powers, which are referred to respectively as actuators and transducers.