Experiments with electromagnets

Jumping Ring expt.gif (888 bytes)

This is a great demonstrator of Lenz's Law, and an extension of the Floating Tube experiment. All that is needed is to slide the AC electromagnet coil over an 8" long bolt, place an aluminum or copper tube over the bolt, and energize the electromagnet for a short time, like a only second! The tube will shoot off the end of the bolt and go sailing through the air. To give it a greater distance, cool the tube in some liquid nitrogen to get it really cold (and make its resistance much lower) then place it onto the bolt and give the coil a short pulse of current. The distance the tube will travel could be twice as far as the warmer tube.

You may find something like this in a science museum (such as the Franklin Museum in Philadelphia, or the Discovery Place in Milwaukee). You push a button on an electromagnet and an aluminum ring is propelled over an arch to another electromagnet. Press a button on the other electromagnet, and the ring is shot back to you. Great fun!

To make one that can shoot a ring several feet into the air, a larger AC electromagnet is wound onto a long laminated core which is much longer than the core is.  When energized, an aluminum ring resting on top of the coil will shoot off into the air. 
Details are given in:

Propulsion without Wheels
E. R. Laithwaite
Hart Publishing Company
New York, NY  1968
(see pages 130-131)