Diamagnetic levitation: Flying frogs and floating magnets (invited)

Contrary to our intuition, apparently nonmagnetic substances can be levitat ed in a magnetic field and can stabilize free levitation of a permanent mag net. Most substances are weakly diamagnetic and the tiny forces associated with this property make the two types of levitation possible. Living things mostly consist of diamagnetic molecules (such as water and proteins) and c omponents (such as bones) and therefore can be levitated and can experience low gravity. In this way, frogs have been able to fly in the throat of a h igh field magnet. Stable levitation of one magnet by another with no energy input is usually prohibited by Earnshaw's Theorem. However, the introducti on of diamagnetic material at special locations can stabilize such levitati on. A magnet can even be stably suspended between (diamagnetic) fingertips. (C) 2000 American Institute of Physics. [S0021-8979(00)68408-6].