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Could Earnshaw be only thinking inside the box

  1. Dec 18, 2013 #1
    Hello PF people
    i just joined the forum after many many months of being driven insane concerning Earnshaw's Theorem, i myself am not a scientist or physicist so i am limited in the amount of knowledge that i have, but my curiosity wont let me accept what everyone else seems to be in agreement with.
    As far as i can understand it is stated that a permanent magnet cannot achieve stable equilibrium, which is why they always attract, as i have discovered on many occasions, my own sense of logic tells me that this is due to each magnet having a single axis, so after thinking about this for a while, i had one of those archimedes moments, although i wasn't in the bath at the time, what if the the single axis became a shared axis, between two permanent magnet, lets say one magnet at point east and one at point west, joined via a rigid connection, my logic tells me that each magnet would cancel the other out, which as far as i can see would create a third state, stability, the problem i foresaw was that the magnets would try and flip the other way, using the north south axis, so using the same process and adding two more magnets to cancel out the potential north south flip, and connecting them with a rigid body would mean the magnets have no where to go, so all they can do is sit there above a surface made of permanent magnets, possibly using a halbach array for the surface, i honestly believe that with a four magnet rig connected to a cross shape, stable levitation of permanent magnets can be achieved. i have already built a platform form for the magnets to be mounted to, but sadly i built it to big, not taking into account that magnetic fields are curved, i did manage to hold the whole thing in one place but its tendency to slide off the field was the only issue, the usual flipping characteristic was not present, the next one i build will be a lot smaller so i can build a surface that it wont slide off. i would seriously love some feedback on this concept. i don't know if youtube links are allowed on here but i put a video on there of me doing this experiment, as i said at the beginning i am not a physicist so please dont be too harsh in your replies.
    Thank you
  2. jcsd
  3. Dec 18, 2013 #2


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    Science Advisor
    Homework Helper

    Trying to argue against math is usually a waste of time, so good luck with your experiment!

    But stable magnetic levitation is possible using diamagnetic materials like water, or even frogs. All you need is a frog, and a VERY strong magnet ... http://www.ru.nl/hfml/research/levitation/diamagnetic/
  4. Dec 18, 2013 #3


    Staff: Mentor

    This is exactly the type of instability predicted by the theorem.
  5. Dec 18, 2013 #4
    i get the arguing against math point, trouble is that wont satisfy my sense of logic until i actually see it not working, i believe the other term for this condition is stubbornness, thank you though for the good luck sentiment, i have seen the frog levitation experiment, all i need to do now is acquire a frog and a very very expensive 10 tesla magnetic coil, anyone have next weeks winning lottery numbers per chance?.
  6. Dec 18, 2013 #5
    so if the sliding off the field is one of the issues, do you think that if the east west magnets where angled outwards then they would centralize themselves, again going back to each one canceling the other out, if one magnet is pushing against the other both with equal force, then the two magnets should stay in one place, as long as the curvature of the field is large enough, I'm also wondering if having a 5th magnet opposite to all the rest and central would not anchor the whole thing somehow.
  7. Dec 18, 2013 #6


    Staff: Mentor

    The point of the theorem is that under the assumptions of the theorem there will always be some direction of slipping. All you can do is design things which violate the assumptions of the theorem.
  8. Dec 18, 2013 #7


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