As outlined above, an induction motor (or a rotating transformer, as they’re less commonly called) is a specific type of AC motor assembly that relies on a spinning, electrically charged rotor to create an EMF around a stator, and thus produce the vital alternating current that the AC motor can then convert into mechanical energy.
Induction AC motors of this kind are also known as asynchronous motors, because the output rotor generally turns at a slower rate than the frequency being supplied to it at any given time. In other words, the motor spins ‘out of sync’ with the power being supplied.
This is necessary because of another key characteristic of a true induction motor; namely that a charge created through electromagnetic induction is the only source of electrical ‘excitement’ the armature receives. If the rotor turned at the exact same speed as the rotating magnetic field on the stator, no current would be induced, and the armature would require another source of excitement in order to generate power. This is what happens in a DC motor, where the current is directly conducted to the armature, or in a synchronous AC motor (see below).