electro pendulums

 
This project uses two cylindrically shaped cow magnets. They are sold at cattle feed stores. People who raise cattle get a cow to swallow such a magnet so that any bits of metal that the cow may eat will be held by the magnet which stays in the cow's first stomach. That way the swallowed metal causes the least harm to the cow. Be sure not to purchase rectangular cow magnets which have the poles at the sides instead of at the ends.
 
Build the structure shown. The top piece is about 3 1/2 by 3/4 by 12 inches, the bottom 5 1/2 by 3/4 by 12 inches and the uprights 3 1/2 by 1 1/2 by 16. A 9/16 inch diameter hole is drilled near the bottom of both uprights to hold the magnets.
 
Use #22 or thinner enameled copper wire to form two coils of 50 turns each with the open center of each coil about 1 inch across. Use a piece cut from a small plastic container or cardboard tube as a form for each coil. Leave at least 2 feet of each wire end extending from the coils. These leads are placed in slots cut in the top board and suspend each coil so that it hangs at the end of a magnet. Scrape or sand away the enamel insulation for one inch on each lead end. Twist the ends together to form a loop circuit as shown in the diagram. Tape or glue the wires along the top board to secure them. Swing one of the coils toward and away from its upright. In a short time the other coil will begin to swing. The first coil to swing cuts through the magnetic field of its magnet. That causes electrical current to flow around the loop circuit just as with any typical electrical generator. The flow of current causes the coils to produce magnetic fields of their own. The second coil moves because it is an electomagnet pushing and pulling against the cow magnet.
 
Notice whether the coils swing in opposite directions or not. Try turning one of the magnets around and see what happens. A somewhat simplified version uses one magnet. A magnet end extends from each of two opposite sides of the single upright. The coils' leads are connected and secured at the top of a block of wood fastened to the top of the upright. Or two disc shaped magnets available at most Radio Shack stores could be attached, one on each end, to a short dowel and that used instead of the cow magnet.