An electric motor is an electrical machine that converts electrical energy into mechanical energy. An electric generator operates in the reverse
direction, converting mechanical energy into electrical energy.
Most electric motors operate through the interaction between the motor's magnetic field and winding currents to generate force. In certain applications, such as in regenerative braking with traction motors, electric motors can be used in reverse as generators to recover energy that might otherwise be lost as heat and friction.
Electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or generators.
General-purpose motors with standard dimensions and characteristics provide convenient mechanical power for industrial use. The largest electric motors are used for ship propulsion, pipeline compression and pumped-storage applications with ratings reaching 100 megawatts. Electric motors may be classified by considerations such as power source type, internal construction, application and type of motion output.