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Spinning Compass

  1. May 21, 2010 #1


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    What happens if you took a compass and surrounded it completely with north poles (and no south poles)? Would the compass just spin repeatedly because it doesn't know what to point to?

    Also, the compass can't spin forever; so I'm guessing it will stop because the magnets can't last forever. Why can't they last forever? Is it because the electrons lose energy?

  2. jcsd
  3. May 21, 2010 #2
    I dont think it would spin at all.
  4. May 21, 2010 #3


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    So if it doesn't spin what would happen? For instance, if you took an ordinary compass and placed 8 evenly spaced magnets with their north poles all facing the compass and very close it, and assuming all magnetic fields are identical in strength, where would it point?
  5. May 21, 2010 #4
    I think it would point in the direction you placed it in.

    Of course if you had 8 north poles surrounding it I assume it would point to the nearest space in between the north poles. But if you could surround it by a 'infinite' amount of N poles such that the filed was completely symmetric, the compass wouldn't be compelled to move at all.
  6. May 22, 2010 #5
    I also think the compass wouldnt spin. The north pole of a magnet is attracting one end of the compass, and the other side would be repelled by the north pole. So they even out.

    But Im not sure on the demagnetizing. I know that most magnets are demagnetized by external forces and so forth, but I wouldnt know what would happen without those.
  7. May 22, 2010 #6
    The electrons in the atoms don't lose energy. A magnet will be demagnetized only when the "magnetic domains" become misaligned. In other words, what makes a magnet "permanent", (i.e., not an electromagnet) is when the material can support the long term alignment of the magnetic domains without the application of an external electromagnetic field.

    Magnetic domains were discovered by physicist Francis Bitter. You can google them and him for more information.

    Back in the day the only known material for mass producing permanent magnets was hardened steel. This was pretty good, but would lose magnetic strength over time, or under various stresses. In the past few decades they have engineered really super magnetic materials that just about nothing in any normal environment will demagnetize. You don't have to worry about your refrigerator magnets, or the magnets in your audio speakers losing any strength in your lifetime.

    Regardless, there is no configuration of permanent magnets that will result in anything spinning. It's been tried by about 400,000 tinkerers since the discovery of lodestone, and none found a way to do it. Once you understand that to get something spinning you need a changing force you can see it can't be done with permanent magnets: their field is not changing, but static. You can get spinning with electromagnets because you can, and motors do, constantly change the strength or direction of the magnetic fields.
  8. May 22, 2010 #7
    Just thought I'd point out that you can do this experiment very easily for very minimal cost. I'm sure you already realized this, but I'd like to encourage you to do that. You will find it very rewarding.
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