Stephen A. Lawrence wrote: > In this case, the energy was put in by spinning up the ring to start > with, and that's the energy we get back out. Whether it resided in the > magnetic field of the ring while the ring was spinning, or in the > inertia of the ring itself, is something which is beyond me just now > (and luckily, for this problem it doesn't really make a difference...).
Agreed from a COE point of view. The point I was trying to lead up to is the way magnets compare to the spinning charged ring. Consider the problem as though we were using another spinning charged ring (B) in place of the dipole box. To start, the dipole box charged ring (B) is already spinning. To get attraction, the two rings need to spin in opposite directions. As we spin up the original charged ring (A), ring B will slow down as it outputs energy to the increasing magnetic field. It will slow down more as the two rings are attracted together increasing the field energy and providing the kinetic energy for the rings relative motion. Assuming similar rings with equal rotation rates at the time when both are spun up, both rings will subsequently provide equal energy. Energy is conserved at all times during these operations. A permanent magnet acts like a dipole box and not like a spinning charged ring. A permanent magnet acts like a spinning charged ring that does not slow down as it supplies energy. This is where questions of ZPE as the source of energy in permanent magnets become involved. With a PM in the box, energy is not conserved during this operation unless we include the energy source from which the PM keeps a constant dipole contribution. In finite element magnetic field simulation programs the PMs are modeled using soft magnetic materials with conductor loops driven by current sources at the poles as the required energy source. This brings us to the way that energy conservation in magnets needs to be described. No net energy is provided by the PM over any complete cycle that returns the magnet to the same field conditions. > > Here's another good one: Does a free-falling charge radiate? As an experimentalist, I would suggest that the answer might be found by studying black holes. I do not have much confidence in many of the theories of modern physics and prefer to direct my efforts to doing experiments suggested by a more conservative approach to how much we think we know. George Holz Varitronics Systems
