Watch this video: Permanent magnets moving relative to a stationary copper tube generate Eddy currents which result in Joule heating of the copper. Simple enough. Let's change the problem to a rotor with 4 (circumferential) permanent magnets rotating inside a stationary (aluminum or copper) tube at some given RPM. 1. Which would heat the stator faster: magnets placed in alternating polarity (NSNS) or the same polarity (NNNN) around the rotor? I think it would be alternating because an area element on the stator would see more variation in the field per revolution. 2. Which would require more torque to turn the rotor: alternating or constant? I think they would be the same because the field strength and relative velocity are the same as the stator element passes each magnet, so the Lorentz force should be the same for both configurations. 3. Why does the alternating magnet configuration generate more heat but require the same amount of torque? Where did I go wrong? Any links or references would be much appreciated.