Jumping Disc (Thomson's Coil)

The Demonstration:
An aluminum ring is launched off of an electromagnet. With the iron bar in the electromagnet, it goes even higher.
Quick Physics:
An electromagnet is just a coil of wires with a current running through it. Electrons are like tiny magnets and when they move (as in a current), they create a magnetic field. The iron core increases the magnetic field of the electromagnet. The ring feels a greater magnetic force, which pushes it higher. The colder the ring it, the less resistance there is and the more current can flow through it. More current means a bigger magnetic field and the ring goes even higher!