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Q & A: magnetic levitation

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Most recent answer: 10/22/2007
Q:
Is it possible to have an object "float" (hover) inbetween to magnets and actually regulate how high or low it can go? If so, how heavy can the "floating device" be?
- Lester Rey (age 17)
Miami, Fl
A:
It is possible with static magnets, but only if you have a "diamagnetic" object- one which expels magnetic fields rather than draws them in. Most objects are either not diamagnetic or else very weakly diamagnetic, so you need to have magnetic fields changing very rapidly in space to hold up an ordinary diamagnetic object. I have seen a picture of a really tiny frog magnetically levitated, and I think thatís as big as it gets. Now one type of material (most superconductors) fully expels magnetic fields. In other words, superconductors are very strongly diamagnetic. Using superconductors, very large objects, like trains, can be levitated.

If you use active feedback circuits to keep changing the magnetic field, you can levitate large objects which have ordinary magnetism. If you try using fixed fields, however, a theorem by Earnshaw says that the situation is always unstable, and wonít stay levitated.

Mike W.

(published on 10/22/2007)

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