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A magnet that won't stop spinning?

  1. Aug 9, 2011 #1
    A magnet that won't stop spinning??

    what happens if a horseshoe magnet is fixed to a a coil such that there is a constant field through the coil?? The initial torque due to the field will spin the coil,but since the magnet is connected to the coil,it will keep sending a field through the coil at the same angle,further spinning the coil and then the process continues.......the coil-magnet apparatus will keep on spinning. Isn't this possible??
     
  2. jcsd
  3. Aug 9, 2011 #2
    Re: A magnet that won't stop spinning??

    .......
     
    Last edited: Aug 9, 2011
  4. Aug 9, 2011 #3

    SteamKing

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    Re: A magnet that won't stop spinning??

    By Jove! I think you've got something! Now, run with it!
     
  5. Aug 9, 2011 #4

    russ_watters

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    Re: A magnet that won't stop spinning??

    No, clearly this violates conservation of energy, so it won't work.
     
  6. Aug 9, 2011 #5
    Re: A magnet that won't stop spinning??

    Why would it violate the law of conservation of energy?The magnet is the source of energy.We are simply using the energy provided by the magnet.No energy is being "magically produced".
     
  7. Aug 9, 2011 #6

    russ_watters

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    Re: A magnet that won't stop spinning??

    No, nagnets do not expend energy by exerting a static force. A magnet is no more a source of continuous power than a spring.

    Perhaps if you drew yourself a picture you'd see that what you are suggesting is like lifting yourself off the ground by pulling on your own shoelaces.
     
  8. Aug 9, 2011 #7
    Re: A magnet that won't stop spinning??

    But where does the magnet-coil model fail?What would actually happen if the set up is made and placed in a zero gravity environment.As long as the the magnet exerts force,the coil would spin.
     
  9. Aug 9, 2011 #8

    russ_watters

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    Re: A magnet that won't stop spinning??

    Nothing will happen. It will not spin because there is no external force to spin it.
     
  10. Aug 9, 2011 #9
    Re: A magnet that won't stop spinning??

    Hmm..but if the magnet were to be detached for a split second,it would spin.That brings me to a more fundamental question-why is there such a big difference between internal and external forces in this case?Why doesn't the internal force in the attached apparatus do anything?After all,it is a field through a magnet[is it because the coil applies an equal and opposite force?]
     
  11. Aug 9, 2011 #10

    Ryan_m_b

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    Re: A magnet that won't stop spinning??

    What do you mean "spin"? What you are trying to describe just wont work. You are trying to create perpetual motion.
     
  12. Aug 9, 2011 #11
    Re: A magnet that won't stop spinning??

    By spin ,i mean that the coil will rotate so as to minimize magnetic flux through it.
    Then again,why wouldn't the magnet-coil apparatus spin-is it because an equal force would be exerted by the coil,thus cancelling out torque due to the magnet?
     
  13. Aug 9, 2011 #12

    uart

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    Re: A magnet that won't stop spinning??

    Yes. If the coil is correctly orientated within the magnet then there is certainly a torque ,due to the current, acting on the coil. For this same orientation and current direction however, the coil itself will induce it's own magnetic poles, which are perpendicular to the main magnet poles and with a N-S polarity directed so as to produce a counter torque on the main magnet.
     
    Last edited: Aug 9, 2011
  14. Aug 9, 2011 #13

    russ_watters

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    Internal forces always sum to zero. Try this:

    Sit on a swivel chair.
    Grab your left shoulder with your right hand.
    Pull.

    Do you start to spin?
     
  15. Aug 17, 2011 #14
    Re: A magnet that won't stop spinning??

    oh yes!! i have realized my mistake! i had not thought about the opposite magnetic field.thank you very much
     
  16. Aug 17, 2011 #15
    Re: A magnet that won't stop spinning??

    I've been sitting in my office chair trying this for a while now and can't seem to do it.

    Am I doing it wrong? Do I pull or push my shoulder?
     
  17. Aug 17, 2011 #16

    Ryan_m_b

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    Re: A magnet that won't stop spinning??

    Is this sarcasm? If so haha, if not it won't work anymore than reaching down and pulling your legs up will make you rise.
     
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