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Re: falling magnet demo



Donald points out an alternative to the copper pipe. This may have a
pedagogic advantage in that students can see the magnet slide down the
trough. The troughs that I have seen were extruded aluminum of "U" shape
cross section. The disadvantage of using super magnets is that students
might be led to think this works only with these super strong magnets.

Roger

In a previous note, I pointed out that our "tube" is made of four or five
nested copper pipes about 2.5 m long. Our magnets are "cattle" magnets about
3" long purchased from a local farm supply store. They are small cylindrical
steel magnets of much lower cost and strength than neodymium. Our machinist
also fashioned a similar cylindrical piece of nonmagnetized soft iron. We
drop this through the tube for comparison with the magnet's fall time. It
also dispels the notion that friction slows the magnet's fall.

Roger



Commercial versions of the demo use the supermagnets in an *aluminum*
tube. Such tubes, in six foot lengths and various diameters, are readily
available in hardware stores.

-- Donald