I got all kinds of different reactions from people from amazement, to an "aha" moment, to nods from the few who already understood the physics behind this. Then I explained what was happening: The magnet induces an electric current within the copper plate, which, in turn, gives rise to a magnet field within the copper, which pulls back against the magnet's motion.  Stop moving the magnet, and the current dissipates, leaving no effect.

Then I explained how this principle is used by induction cooktops, where a circuit inside the unit creates a varying magnetic field just under the top surface.  The magnetic field induces a current in the bottom of the cookware sitting above it, causing it to heat up.  (Copper doesn't work very well because it doesn't offer enough resistance to the induced currents and thus won't heat up enough.  Iron or steel work much better.)

Then I explained how they could try magnetic induction right at home by buying a single burner unit for around $100 and just use whatever cookware they have that will work with it.  My goal is to dispel the myth that homeowners have to discard all their cookware, buy a new stove, or remodel their kitchens.  While explaining this, I handed each guest an information sheet with details. Unfortunately, I ran out of literature before the end of the festival, so I've prepared an updated PDF version here for anyone who didn't get one, and for anyone who couldn't make it to the festival.  Just click on the link below to download an updated copy.