A third set of losses arises from the motor’s shaft bearings and the motor’s internal windage. Ball-bearing friction torque is typically 0.001 to 0.002 times the load, and unless the motor drives through gears or belt, the only load is the weight of the rotor. Bearing loss is small. That leaves windage, which in air-cooled motors is mainly the power consumed by a small fan attached to one end of the rotor. As you probably know, in flywheel energy-storage systems, fast-spinning rotors would rapidly slow down from churning air, so they are enclosed, pumped down, and kept under vacuum. Thus, in motors turning at usual speeds, some torque is lost in the vigorous air turbulence in the small air gap between stator and rotor.