The motor rotor requires a torque to start its rotation. This torque or moment is usually produced by magnetic forces developed between the magnetic rotor poles and those of the stator. An engine can not be operated if it is made exclusively of permanent magnets.

This is easy to verify, because not only will there be no initial torque to ‘trigger’ the movement if they are already in their equilibrium positions, as they will only swing around that position if they receive an initial external ‘jerk’.

Forces of attraction or repulsion, developed between stator and rotor, ‘pull’ or ‘push’ the movable rotor poles, producing torques, which cause the rotor to rotate faster and faster, until the frictions or loads attached to the shaft decrease the torque to the value ‘zero’. After this point, the rotor rotates with a stable angular velocity. Both the rotor and the motor stator must be ‘magnetic’, as these forces between poles produce the torque required to make the rotor rotate. Even though permanent magnets are often used, especially in small motors, at least some of the ‘magnets’ of a motor must be ‘electromagnets’.

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