How does the electric motor rotor rotate?

The rotor of the electric motor needs a torque to start its rotation. This torque is usually produced by magnetic forces developed between the magnetic rotor poles and those of the stator.

Forces of attraction or repulsion, developed between stator and rotor, ‘pull’ or ‘push’ the rotor’s movable poles, producing torques, which cause the rotor to rotate faster and faster, until the frictions or loads attached to the shaft reduce the Torque to the value ‘zero’. After this point, the rotor rotates with a constant angular velocity.

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At least some of the ‘magnets’ of a motor must be ‘electromagnets’. An engine can not run if it is built exclusively with permanent magnets, because not only will there not be the initial torque to ‘trigger’ the movement.

A simple electric motor consists of a coil that rotates between two permanent magnets. The magnetic poles of the coil (represented by the magnet) are attracted by the opposing poles of the fixed magnets. The coil rotates to take these magnetic poles as close as possible to each other, but when it reaches that position the current direction is reversed and now the poles that face repel each other, continuing to propel the rotor.