The synchronous electric motor has the rotor with number of poles corresponding to the number of poles of the stator winding. During normal stepping operation, there is no relative motion between the rotor poles and the magnetic field flux of the stator (stator poles), ie they are in perfect synchronism. The magnetic field of the rotor always intends to align with the magnetic field of the stator, but the two magnetic fields are never correctly aligned, because the existence of a sturdy torque generates a lag between the fields, even if they are running at the same speed.
Even when it is idle, the motor has a strong torque due to the friction of the bearings and the ventilation system. This lag generates an angle, called a load angle, or torque angle. This loading angle rises as the sturdy torque increases. In turn the “output power” of the motor will depend on the total losses in the motor, which are the total losses in the stator copper, total losses in the rotor copper, losses by friction and ventilation and losses in the iron. https://www.mrosupply.com/electrical/extension-cords-reels/cord-reels/773434_l5550123x_reelcraft/