String a wire between the poles of the large magnet and connect
the ends to a power supply. Turn on a small current through the
wire and it will jump out. Reverse the polarity and the wire will
jump into the magnet.
Also available as a variation on this concept is the "jumping
speaker" demo. There are a couple speakers in drawer 43 that look
like the above photo and are detached from their bases with 2
wires coming out from the speaker coil. Make sure the speaker is
sitting fairly flat and snug in the speaker base, then connect the
wires to a 9V battery (either by tapping the battery to the leads
as shown in the photo, or by using alligator clips) to see the
speaker jump out of the base.
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