220V Cooling Fan rotor rotation

"220V Cooling Fan" is to provide the use of an alternating power supply: single-phase AC motor is only one winding, the rotor is a squirrel-cage. When single-phase sinusoidal current through the stator windings, the motor will produce an alternating magnetic field, the strength and direction of the magnetic field at any time intercropping sine law, but in the spatial orientation is fixed, so called the alternating magnetic field pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two at the same speed, rotation of the rotating magnetic field opposite to each other, when the "220V Cooling Fan" rotor is stationary, the two rotating magnetic field generated in the rotor two equal and opposite torque, so that the combined torque is zero, so the motor can not be rotated. When we use the force of the motor to rotate in one direction (eg clockwise rotation), then the movement of the rotary cutting magnetic field lines and clockwise rotation of the rotor becomes smaller; "220V Cooling Fan" rotor and counterclockwise direction cutting magnetic field lines motion rotating magnetic field becomes large. This balance broke the total electromagnetic torque generated by the rotor will no longer be zero, the rotor will push along the direction of rotation from