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Re: more Japanese gyro-dropping



Gary's observation, and a challenge presented by Herb, made me think that
a magnet falling through a solenoid and a solenoid folling through the
terrestial magnetic field have something in common. Can a rapidly rotating
metallic disk be viewed as a current loop? The uniform magnetic field would
create and external torque on the gyroscope but not a net force. I have
nothing to suggest; just thinking about both problems.

I suspect that the "magnetic braking" effect of eddy currents must play a
role in the case of the magnet falling near the copper winding. The effect
may be small but not negligible. Local current loops can exist in short
segments of copper, even when the input resistance of the oscilloscope
is very large. Just recall what happens when a magnet falls through a
copper pipe which has a slot from one end to another. The magnetic braking
is nearly as strong as it is in a pipe without a slot. I have a setup to
demonstrate this.
Ludwik Kowalski