Jumping Rings with AC or DC driving

A large coil has a long metal cylinder, extending well past the body of the coil, put into the middle and it is wired up to permit either 120 V AC or DC voltage to be applied. A copper ring that has been encased in liquid nitrogen is then put on top of the coil by threading it around the cylinder. In the case of DC voltage being applied the inital kick of rising electritciy and hence a changing magnetic field is adequite to launch the ring to the top of the metal cylinder and then it drops down again. In the case of AC the initial change doesn't generate an initial magnetic field change strong enough to launch the ring, instead it hovers above the coil (camera must be used to show this.)