Levitron: The Amazing Anti-Gravity Top
Levitron is an eccentric educational toy consisting of a small metallic top, a heavy black base to spin it upon, and a thin plastic layer between the two. Get the top spinning, then lift it off the base by moving the plastic layer, and watch as it hovers several inches above the base as it spins, a defiant kick in the pants to fun's arch nemesis gravity.
Getting the top to work right, however, is a painstaking and twiddly process. With the set are provided an assortment of ring-shaped brass and plastic weights in various colors and sizes. (And a tiny rubber washer to hold it all on, but a rubber band works great if you're the washer-losing type.) With too little weight on board, it shoots off across the table, and with too much, it just acts like an ordinary top. Even more annoying, its ideal weight changes by the minute, so the fine-tuning never completely ends.
Levitron's secret is that the top itself and the black slab it spins above are magnetized with opposing polarities. When the weight and position of the top are perfect, repulsion between the north poles of the twin magnets causes it to find a point of equilibrium where magnetism is balanced out by gravity.
The weight of the top needs constant precise adjustment because it plays a part in determining the height of the equilibrium point, and minute temperature changes alter the force of the two magnets. Therefore, adjustment is needed to compensate for climate. So the next time Levitron just won't get any air, you can at least save face with a scientific explanation.
Levitron was patented in 1995 by a Seattle-based company called Fascinations. ("Wonders created by Physicists".) Since its invention, it has been quite popular; later versions of the toy called Platinum and Omega Levitron place it on an easily adjustible tripod base, and a device called the Perpetuator piggybacks on top of the base, generating electromagnetic radiation to make the top spin indefinitely.
Sources: www.levitron.com and of course, this weird floaty toy I got for Christmas about eight years ago, and finally got to work two hours ago.