The internal forces of the electric motor cause the rotor to rotate, which is called the Lorentz Force. If an electron passes through a magnetic field, it will suffer a force. If there is a current passing through a wire through the magnetic field, it will suffer a force proportional to the product of the current and the magnetic field.
To maintain the constant torque in the rotor two things can be done as, reverse a half cycle of the current in the whole winding and doing this the torque will always be in the same direction, will not be alternated, and also the additional windings can be placed with different angles around of the motor, causing the torque to become the sum of the torques of these windings rab vxcb . This is always greater than zero, but not constant, this variation being called the ripple of the torque.
We can calculate the direction of the force using the Right Hand Rule. The index finger of the right hand points in the direction of the current and the middle finger points in the direction of the magnetic field, the thumb will give the direction of the force. Note that the single wire will be replaced by a loop. The forces on this wire will cause a rotation in the loop and between the magnetic poles, this loop will behave like two wires with currents flowing in opposite directions.