How Electric Motors Work

Magnetism

Magnetism is the force that creates rotation for a motor to operate. The poles of a permanent magnet are connected by magnetic lines of force. The principle of magnetism states that unlike poles are attracted to one another while like poles repel. AC motors operate on this principle.
When two bar magnets come into close proximity, the resulting attraction and repulsion create force. The magnet on the left is stationary and cannot move. The one on the right is free-turning and rotates. As the "North" pole of the rotating magnet moves away from the like pole of the stationary magnet, the "South" pole of the rotating magnet is attracted towards the opposite pole of the stationary magnet. Since unlike poles attract, the turning magnet rotates until the "N" and "S" poles come together. When this occurs, both magnets are satisfied and no further action will occur.

How Electric Motors Works

Electric motors function on the principle of magnetism; where like poles repel, and unlike poles attract.

In a simple motor, a free-turning permanent magnet is mounted between the prongs of an electromagnet. Since magnetic forces travel poorly through air, the electromagnet has metal shoes that fit close to the poles of the permanent magnet. This creates a stronger more stable magnetic field. (The electromagnet functions as the stator, and the free-turning magnet is the rotor.) Fluctuating polarity in the electromagnet causes the free-turning magnet to rotate. The poles are changed by switching the direction of current flow in the electromagnet.
The direction of current flow can be changed in one of two ways. In a DC motor, connections must be interchanged at the battery. AC current oscillates on its own.

The stator in an AC motor is a wire coil, called a stator winding. It's built into the motor. When this coil is energized by AC power, a rotating magnetic field is produced.
When a magnetic field comes close to a wire, it produces an electric current in that wire. This is called induction. In induction motors, the induced magnetic field of the stator winding induces a current in the rotor. This induced rotor current produces a second magnetic field necessary for the rotor to turn.

Induction motors are equipped with squirrel rotors, which resemble the exercise wheels often associated with pet rodents like gerbils. Several metal bars are placed within end rings in a cylindrical pattern. Because the bars are connected to one another by these end rings, a complete circuit is formed within the rotor.

Consider this close-up of a 2-pole stator and one of its rotor bars. Alternating current flowing in the stator causes the poles to change rapidly, from north to south and back again. If the rotor is given a spin, the bars cut the stator lines of force. This causes current flow in the rotor bar. This current flow sets magnetic lines of force in circular motion around the rotor bars. The rotor lines of force, moving in the same direction as those of the stator, add to the magnetic field and the rotor keeps turning.