Re: falling magnet demo

[PHRP@FHSUVM.FHSU.EDU (Roger A. Pruitt)]

We found that a single, thin-walled copper pipe did not produce large enough
eddy currents to slow the magnet appreciably. We thought about having a
gunsmith bore out a large copper bar, but first tried nesting copper pipes
of increasing diameters. This worked extremely well, and we have been using
a 2.5 meter pipe of this construction successfully for the past seven years. 

Roger

> I tried a classic demonstration of dropping a magnet through a copper
> tube at the same time as dropping an unmagnetized bar.  They both
> landed at the same time.
> Since one possible explanation was that the magnet's speed was not
> great enough, I set a pvc tube on top of the copper tube so that
> the magnet would have a significant speed when it reached the copper.
> Still, they both fell with normal acceleration.
> Can anyone explain why the magnet was not slowed when falling through
> the 50 cm long copper pipe?
> Thanks,
> Don Greenberg