On Tue, Oct 18, 2011 at 1:15 AM, David Roberson <[email protected]> wrote: > >>From: Harry Veeder [email protected] > >>If the "law of inertia" is universally true, some sort of centripetal >>force is required to keep the disc revolving in a circle as it moves >>above the magnets. I can vaguely grasp how the phenomena of locking >>preserves the tilt of the disc, but how does locking bring about the >>necessary centripetal force? > >>Harry > It is a beautiful presentation and raises several good questions such as: > > It appears to take force to get the disk to move close to the supporting > magnetic structure. This suggests that energy has to be applied to the > system as the force occurs over a finite distance. Then if the disk is > removed, force again must be applied in the opposite direction. More energy > is absorbed by the system of magnet and disk. Now, where does the energy go > which is supplied? I understand that a superconductor does not allow > resistive loss from current flow so I suspect magnet must gain energy. Does > it actually become warmer as a result of this operation? > > Dave
Hmmm it obvious now. Clearly a superconductor can be made to exhibit both attractive and replusive behaviour simultaneously through the effect of "flux trapping". The attractive behaviour is what keeps the disc on the tract. However, when I took undergraduate physics 25 only the meissner effect which results in repulsion was mentioned. After doing some on line research I found out it was considerably more difficult to produce flux trapping with the superconductors that were available in the 80's. I guess the impractical nature of demonstrating fluxtrapping meant the phenomena need not be mentioned. Harry
