Dave Johnson made this awesome mechanism, which he calls a Magnet Machine, that illustrates the concept of inductive eddy currents. He writes:
This machine manipulates small spherical rare earth magnets, slicing one at a time from the end of a long chain, moving it around a bit, then dropping it back to re-connect at the tail end of the chain.
It also demonstrates a little snippet of science called eddy currents. Watch how slowly the magnet falls through the aluminum tube compared to falling through air: the falling magnet generates an electrical current in the tube, and that current in turn generates a magnetic field that opposes the movement of the magnet, slowing it down dramatically. See http://en.wikipedia.org/wiki/Eddy_current if you want more.
I made this machine for my father-in-law for his 75th birthday: astute viewers equipped with video analysis software and way too much time on their hands might find that the magnet drops 75mm from the tip of the slicer until caught by the lifter, and that the lifter then drops it through a 75mm long aluminum tube.
Outstanding! Great work, Dave!
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The slicing and moving mechanism on the outside strikes as incredibly clever mechanical engineering. The inside, with the chain of spherical magnets, snaking around the inner clock-work, looks like a bunch of god damn voodoo! Beautiful, thank you for sharing.