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At 12:27 PM -0700 4/30/98, William Beaty wrote:
Musings about LN2: as conductivity decreases, the magnet falls slower, but
at some point a further decrease in conductivity will cause the magnet to
fall faster. The skin-depth effects and the Lenz-law resistive heating
and braking effects don't vary with temperature in the same way. At very
low resistance, the skin depth becomes so small that significant fields
won't "sink into" the metal, and so the braking force will be reduced and
the magnet will fall. Also, once the magnet starts to fall faster, the
skin depth becomes even smaller and the braking becomes less. As a
result, the magnet would "break loose" from the braking effect, and
suddenly drop down the tube with very little EM friction. At least,
visual/intuitive thinking tells me this is so.
Sorry Bill, but I gotta disagree on this visual/intuitive thinking result.
MY visual/intuitive thinking sez you'll be approaching a superconductive
state and I use the copper pipe as a lead-in for the HTc levitation exp. If
the pipe were a PERFECT conductor the magnet wouldn't fall AT ALL!!!