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Q & A: levitating mercury?

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Most recent answer: 07/18/2009
Q:
I have read some articles about ancient useage and perhaps,not a true useage of mercury being enclosed in a sealed container and being heated to a pretty high degree,and this caused the container to levitate.It is probably just some kind of fantasy...anything to it?
- D.Weiss
Youngstown,Ohio
A:
Sure sounds like a fantasy to me.

Mike W.

(published on 01/23/2008)

Follow-Up #1: levitating metals

Q:
There are a couple of ways of looking at this. If you get a metal like mercury or lead, and heat it up enough, then you can "hold" it in your hand, it will "levitate" on a buffer of water vapour that evaporates from your skin... looks VERY cool and it's easy to screw up. Or you can levitate a drop of mercury (actually, up to about an 11mm diameter) over a strong magnetic field because the magnetohydrodynamic forces cause freaky turbulence (they think) inside the droplet. But to just heat it and have it levitate... no.
- Bernard
Perth, Australia
A:
That idea about holding hot mercury or lead suspended on a little water vapor from your skin sounds really bad, as you indicate. Even if somehow you manage not to get burned, you've got hot metal emitting toxic vapors.

If any conducting metal drops toward a strong magnetic field, eddy currents will be generated in the metal. The magnetic field of these currents will repel the magnetic field already there. However, the eddy currents are dissipated by resistance in the metal, allowing the metal to fall toward the magnet, just somewhat slowed.

Even if some turbulent liquid flow gets going in the liquid mercury, I don't see how it could be sustained without some additional energy source. So a mercury drop should fall, roughly similarly to other pieces of metal.

The previous question about  mercury in sealed containers seemed to involve some old myth.


Mike W.

(published on 07/14/2009)

Follow-Up #2: diamagnetic levitation

Q:
Can the diamagnetic property of any metal be exploited for its levitation(even though it may require a good big magnitude of magnetic field)?Can the same idea be used for levitating humans, without damaging the body functioning()due to high magnetic fields)?Thanks
- Nimish (age 17)
Mumbai, India
A:

Typical metals are so weakly diamagnetic that you'd need a very strong field changing over a very short distance to provide enough force to levitate them in the Earth's gravitational field. That means working with a very small sample of the metal, not a large object. Still, it's possible in principle.

Some metals are not diamagnetic but rather weakly paramagnetic. Earnshaw's theorem proves that such paramagnetic material cannot be levitated by any combination of static fields. Such metals can be levitatedusing the eddy currents induced by ac fields, but that requires a steady energy input.

Very small animals (e.g. tiny frogs) can be levitated in dc fields thanks to their diamagnetism. The problems and the strength of the required fields become enormous for larger animals such as ourselves. Although I believe that people are not seriously hurt by the largest standard lab fields (say 15 Tesla) , those would not be nearly large enough to levitate anyone.

There's a nice discussion here: https://en.wikipedia.org/wiki/Diamagnetism.

Mike W.


(published on 07/18/2009)

Follow-up on this answer.