An AC motor is an electric motor driven by an alternating current. The AC motor commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft producing a second rotating magnetic field. The rotor magnetic field may be produced by permanent magnets, reluctance saliency, or DC or AC electrical windings.
When an AC motor is in steady-state rotation (motion), the magnetic fields of the rotor and stator rotate (move) with little or no slippage (near synchrony). The magnetic forces (repulsive and attractive) between the rotor and stator poles create average torque, capable of driving a load at rated speed. The speed of the stator rotating magnetic field and the speed of the rotor rotating magnetic, relative to the speed of the mechanical shaft must maintain synchronism for average torque production by satisfying the synchronous speed relation. Otherwise, asynchronously rotating magnetic fields would produce pulsating or non-average torque.