Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I know that it's possible to make an object levitate using an electromagnet to hold it up. But is it also possible to do this with regular magnets? Is there a special kind of magnet I need in order to have one powerful enough to hold an object up?

I'm asking because I have this idea in mind where I want to make a decorative item that is levitating an inch or so above its container.

alt text

A is the object I want to levitate.
B is the container.
C shows the magnetic field that is repelling A and B from each other achieving the levitation.

The size of this would be as small as a food plate, maybe even smaller. B is barely a pound or two in weight.

Is that possible?

share|improve this question
    
This site is not for home improvement or do-it-yourself projects or interior decoration. It's for discussion of physics. Your question is pretty close to being about physics - if you edit it to just ask what physical phenomena could be used to levitate an object without electromagnetism, or how strong a magnet would have to be to do so, it'd be fine. However, asking about cost estimates is off topic here. (Also I'd like to see your first paragraph gone) If you change the question to focus on the physics and not the implementation aspects, I'll gladly reopen it. –  David Z Dec 18 '10 at 5:24
3  
@David -- besides; how can a title like that not "generally relate to Physics"? –  BeemerGuy Dec 18 '10 at 6:37
3  
@David -- if instead of closing it you edited it yourself and deleted the first paragraph, then none of this argument would have happened. –  BeemerGuy Dec 19 '10 at 4:59
1  
@BeemerGuy: I suppose that's true, but I'm kind of wary of making major edits to questions because I can never be sure if I'm getting at the real point of the question as the asker (you) intended it. Plus, some people get offended if you change what they write too much (though I guess they shouldn't really, given that everything is community-editable here). I'm still getting used to this mod-powers thing ;-) Anyway, I've reopened your question, but I still think it could be made better. If you don't mind, I can try to edit it in that way, hopefully without changing what you're really asking. –  David Z Dec 19 '10 at 5:32
1  
@David -- have at it! I don't mind. You're the mod. –  BeemerGuy Dec 19 '10 at 5:39

3 Answers 3

up vote 11 down vote accepted

The references in other answers to the Wikipedia pages about Earnshaw's theorem and Magnetic levitation are right on; you absolutely cannot have stable, static magnetic levitation using only ferromagnets. However, at the time of my posting, both other answers contain misinformation.

Kakemonsteret's answer is incorrect*, because Earnshaw's theorem is not the end of the story. If you violate the assumptions of Earnshaw's theorem, its conclusions are no longer valid. There is a special kind of magnet Earnshaw's theorem didn't consider, which you can use for stable, static magnetic levitation: a diamagnet.

Superconductors are strongly diamagnetic, but I suspect using a superconductor is an unsatisfactory solution, unless you have liquid nitrogen on tap. Weaker room-temperature diamagnets like bismuth and pyrolytic carbon don't support much weight, but they will levitate forever and don't require cooling, electricity, or attention.

user879's answer links to the excellent Wikipedia page on magnetic levitation. I'd like to emphasize that this page explicitly discusses diamagnetic levitation, which I think is the closest answer to the spirit of your question: a special type of magnet that makes an object levitate without using an electromagnet. However, the answer goes on to state that a bowl of [ferro]magnets would also work. This is false.

I spent a full summer in high school trying to float a tennis ball covered in fridge magnets above a bowl lined with fridge magnets. I failed; I wasn't violating any of Earnshaw's assumptions. Years later when I finally learned Earnshaw's theorem, I was relieved to realize my failure was predictable, since my goal was provably impossible.

So, buy some strong ferromagnets, buy some strong, light diamagnets, scale down your design's ambitions to something very light, and start building your decorative item.

Don't put your credit cards or your hard drives near it.

*EDIT: This answer has been updated, and now mentions diamagnets.

EDIT: I can't believe I forgot to mention my favorite aspect of Earnshaw's theorem: it proves there's no such thing as solid objects! This is the single most obvious everyday evidence for quantum mechanics. If you see an apparently static, stable object that isn't held together by gravity, then it can't be modeled as a collection of point charges interacting through Newton's laws and Maxwell's equations.

share|improve this answer
1  
@ Andrew You are right, it has been done. there are pictures : en.wikipedia.org/wiki/Diamagnetism . even a live frog !! –  anna v Mar 9 '11 at 5:19
    
@anna: if you think the wrong answer has been accepted, there really isn't anything that can be done about it except casting your votes accordingly, and leaving a comment on the answer and/or the question. –  David Z Mar 9 '11 at 5:35
1  
""buy some strong, light diamagnets,"" I do not like this "diamagnets". A magnet in my opinion is something which is permanently polarized. I'd prefer "diamagnetic material". –  Georg Mar 9 '11 at 8:54
    
@Georg I'm not sure how much to trust internet dictionaries, but 'diamagnet' seems to be a word. Feel free to edit my answer if this still bothers you. –  Andrew Mar 9 '11 at 20:40
1  
thanks for your tenacity; I think you brought back life into my idea =) –  BeemerGuy Mar 10 '11 at 23:17

Earnshaw's theorem proves that using only static ferromagnetism (like refridgerator magnets, which have a very slowly changing magnetic field) it is impossible to stably levitate against gravity.

http://en.wikipedia.org/wiki/Earnshaw%27s_theorem.

Diamagnetic materials might be used to levitate objects.

share|improve this answer
    
I do not think Earnshaw's theorem applies for this case as a)It is not a point charge we are talking about, b)Electromagnetism is not the only force applying on the object. –  Cem Dec 18 '10 at 22:57
    
At a minimum this statement needs to be qualified. Basically Earnshaw's theorem does not deal with all possible configurations of stuff one might use to manage levitation. –  dmckee Dec 18 '10 at 23:37
2  
@Cem @dmckee -- actually, in the wiki, the forth paragraph of the Explanation section says "this theorem also states that there is no possible static configuration of ferromagnets which can stably levitate an object against gravity, even when the magnetic forces are stronger than the gravitational forces." –  BeemerGuy Dec 19 '10 at 5:52
2  
@kakemonsteret Theorems are fine, as long as their premises are kept. Demonstrations are better, look at the pictures: en.wikipedia.org/wiki/Diamagnetism –  anna v Mar 9 '11 at 6:33
1  
@kakemonsteret if you want to keep this as the chosen answer you have to add the correct data for the answer to the question, that there exist diamagnetic materials which might be used to levitate objects, without electroctromagnetism. I think Andrews addresses the question better. –  anna v Mar 9 '11 at 6:41

yes, you can. Not easily though.

My favorite is the Meisner effect. It would require a superconductor for B, which would most likely require liquid nitrogen. Basically, the levitating magnet (A) would create an current in the superconductor (which has "zero" resistance). The current would then go for as long as the superconductor superconducts, creating a magnetic field, which would repulse A.

For more explanation, check out wikipedia. Basically, a I have no idea how much this would cost. Although, the liquid nitrogen needed would most likely make it impractical. By the way, there are no room temp superconductors currently known.

more methods are shown here: http://en.wikipedia.org/wiki/Magnetic_levitation. Some methods shown there do in fact use electricity, but some don't. Check out the spin-stabilized levitation. Very cool.

The last would be to build a bowl of magnets. If you arrange it right, you should be able to get it stable.

share|improve this answer
    
Wait, it all made sense until your last comment -- so it is possible with basic magnets arranged in a certain way? So need for superconductors? –  BeemerGuy Dec 18 '10 at 3:21
    
@user879 See kalle43's answer. I don't think you can use just a bowl of magnets. –  Mark Eichenlaub Dec 18 '10 at 5:30
    
I don't know about the rest, but I know you can't use a bowl of magnets. –  Bruce Connor Dec 18 '10 at 15:54
1  
Superconductors are not ferromagnetic -- they are super-diamagnetic, this make them levitate. Some room temperature diamagnetics also levitate, but the effect is subtle. –  mbq Dec 19 '10 at 9:58

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.