# Levitron toys vs Earnshaw's theorem **URL:** \ **Category:** Factual Questions\ **Created:** [November 22, 2012, 4:45pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847 "2012-11-22T16:45:48Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Greg\_Charles](https://avatars.discourse-cdn.com/v4/letter/g/839c29/32.png) [@Greg\_Charles](https://boards.straightdope.com/u/Greg_Charles)\ **Post date:** [November 22, 2012, 4:45pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/1 "2012-11-22T16:45:48Z")
In an ad Edmund’s sent me about their [Levitron Globe](http://www.scientificsonline.com/levitron-anti-gravity-globe.html), they claimed it violated Earnshaw’s theorem. Based on [Wikipedia](http://en.wikipedia.org/wiki/Earnshaw's_theorem), it does seem impossible, but there are some “loopholes”. Which loophole is this toy using? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 22, 2012, 4:51pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/2 "2012-11-22T16:51:54Z")
The gyroscopic effect stabilizes the levitator. It’s not stable when not spinning. ---
**Author:** ![Greg\_Charles](https://avatars.discourse-cdn.com/v4/letter/g/839c29/32.png) [@Greg\_Charles](https://boards.straightdope.com/u/Greg_Charles)\ **Post date:** [November 22, 2012, 5:30pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/3 "2012-11-22T17:30:08Z")
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? ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [November 22, 2012, 5:45pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/4 "2012-11-22T17:45:06Z")
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). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 22, 2012, 6:06pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/5 "2012-11-22T18:06:36Z")
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. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 22, 2012, 6:19pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/6 "2012-11-22T18:19:36Z")
> [@Chronos](#): > > 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](http://mods.x-cart.com/templates/27-dresscode/images/P/demo_store_p4017-01-01.jpeg), which is not dynamic - it’s just gyroscopic. ---
**Author:** ![Greg\_Charles](https://avatars.discourse-cdn.com/v4/letter/g/839c29/32.png) [@Greg\_Charles](https://boards.straightdope.com/u/Greg_Charles)\ **Post date:** [November 23, 2012, 6:22am UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/7 "2012-11-23T06:22:45Z")
> [@Chronos](#): > > 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. 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? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 23, 2012, 4:24pm UTC](https://boards.straightdope.com/t/levitron-toys-vs-earnshaws-theorem/641847/8 "2012-11-23T16:24:02Z")
Magnets can gradually change in strength due to the temperature or magnetic field of their environment, or rapidly due to traumas like getting dropped.