In an ad Edmund’s sent me about their Levitron Globe, they claimed it violated Earnshaw’s theorem. Based on Wikipedia, it does seem impossible, but there are some “loopholes”. Which loophole is this toy using?
The gyroscopic effect stabilizes the levitator. It’s not stable when not spinning.
Well, that’s a thought. The ad doesn’t mention it rotating, but a found a video that shows it does. It’s quite slow though, maybe one rotation every two to three seconds. That’s really all it takes? If it slowed down any more, it would fall off?
Earnshaw’s theorem does not apply to diamagnetic materials (which is how they get frogs to levitate). Alternatively, the magnetic field could be altered via some feedback mechanism in response to the motion of the globe (Earnshaw’s theorem applies only to static configurations).
It’s dynamic. There’s a sensor that somehow monitors the position of the globe and adjusts the field accordingly. These things (at least, the way they’re usually designed) are also extremely fiddly: If the strength of the magnet changes at all, you won’t be able to balance it just right.
I didn’t look at the link.
I have this one, which is not dynamic - it’s just gyroscopic.
Ah, so it’s really balancing the globe like a person would … detecting shifts and making adjustments. That’s sort of amazing actually.
Fiddly, huh? So these things often go bad after a while? Do magnets naturally change in strength, or is it unusual?
Magnets can gradually change in strength due to the temperature or magnetic field of their environment, or rapidly due to traumas like getting dropped.