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Constantly Moving Magnet

  1. Dec 17, 2007 #1
    Is it possible to make a magnet move constantly up and down, insider a container for example, without touching it or forcing it to move?

    I dont know much about Physics but wanted to ask this question as its been bothering me for a few days!!!!

    I was thinking about how magnets may repel and attract each other and by having magnet at both ends of a container or tube, a magnet in the middle may constantly move due to this attract/repel effect

    Is this possible?
  2. jcsd
  3. Dec 17, 2007 #2


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    In a vacuum, maybe. In air, absolutely not. Conservation of energy + air resistance = no way jose.
  4. Dec 17, 2007 #3
    Are there any applications that use it in a vacuum? What if the magnets are in an air tight tube?
  5. Dec 17, 2007 #4


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    Staff: Mentor

    The question appears to me to be a logical contradiction. How can you "make" anything move without "forcing" it to move?

    Theoretically, an object on a spring would bounce up and down forever if there were no friction, but it still requires a force to get it moving in the first place.
  6. Dec 17, 2007 #5
    Thanks Russ. I was thinking along the same lines.

    Further, even assuming you had a magnet, say in a tube with say, Bismuth ends so that no matter which pole faces it the pole is repelled, and this magnet is already moving towards one pole or the other, sooner or later due to hysteresis losses and the plain old dampening effect that it implies the magent in the center will come to rest somewhere between the two extremes without some outside action.

    Otherwise it would be a perpetual motion machine. (From the perspective of say a Rankin Cycle a clear impossibility.)
  7. Dec 17, 2007 #6
    I thought that it is ok for something to move from one point to another until infinity, but it can't ever do useful work while doing so... or give you more work back then what you put into it - that would be a violation.

    so i think, to answer the question the poster had: If you theoretically created a PERFECT vacuum, displaced the magnet in the middle by some distance (hence put in some potential energy), and then let it go, then yes, it would bounce around forever, converting always between potential energy and kinetic energy. Its not really useful though :)
  8. Dec 17, 2007 #7
    Mephisto. That would seem to be correct, but it not only requires a perfect vacuum, but perfect elasticity in the magnetics.

    In other words the magnetic materials can have no hysterysis losses. Can't convert some tiny percentage of the force they receive into heat, nor electricity, nor expansion, nor compression, nor motive or nuclear forces strong or weak of any kind.

    Given that, yes it would bounce forever. But in the real world we can't build any such materials yet. And even if we could good old Heisenburg would start spinning in his grave if we thought we could monitor such a perfect confluence without disturbing it.
  9. Dec 18, 2007 #8


    Staff: Mentor

    An accelerating charge radiates, does an accelerating magnet also radiate?
  10. Dec 18, 2007 #9


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    Science Advisor
    Homework Helper

    Easy, Just change the frame of reference.

    For example: you can make the Sun move by making the Earth stationary :smile:
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