Spinning magnetic coins

A simple, clear demonstration of the effect of magnetization! Equipment: 0.33L cans, ruler, neodymium magnet, iron coins, straw. Construct a bridge: suspend a ruler between two supports. Set a magnet on top of the ruler. Suspend some coins by the neodymium magnet under the "bridge," forming a coin chain. Blow on the lowest coin through a straw. Notice how fast the coin rotates. Modify this experiment by constructing a tower of coins balanced on a can, attracted to the magnet on the ruler above. Now you can spin the whole tower! Ferromagnetic materials, such as iron or nickel, can become magnetized if placed in an external magnetic field. We used coins made of steel, an alloy consisting of mostly iron, a small amount of carbon, and some additives. When these coins encounter an external magnetic field,