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Can magnets defy the law of energy conservation?

  1. Dec 15, 2012 #1
    I'm pretty sure it cannot, but if I put a common bar magnet close to another magnet, they will move towards each other. I don't have much of a background in physics, but it seems to me that the kinetic energy is coming out of...nowhere. I can repeat this experiment as many times as I like but the magnetic attraction does not decrease. Where is the energy coming from? What is being converted into kinetic energy?

    For all the physics intellectuals, I'm only in grade nine so please don't use:
    1. Fancy words no layman can understand
    2. No fancy equations that include processes, functions, and the like

    And please use common analogies. That would be great. Thank you.
  2. jcsd
  3. Dec 15, 2012 #2


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    It's coming out of the magnetic field.

    The magnetic field gets is energy from you. (by separating the magnets)
  4. Dec 15, 2012 #3
    It works the same way as gravity. You can hold a ball over your head and let gravity pull it down, or hold a magnet next to a bit of metal (or another magnet) and let one pull the other. When you're done, you have to put energy back into the system to separate them: be it a ball and the ground, or two magnets.
  5. Dec 15, 2012 #4


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    The energy comes from you.

    When the magnet was made it was given Potential Energy relative to all the other iron in the universe. When you bring a bit of iron near to the magnet it looses PE and gains KE. When it hits the magnet the KE is dissipated as heat (and sound perhaps). If you want to repeat the trick using the same bit of iron you have to expend energy pulling it off the magnet and restoring it's PE.
  6. Dec 15, 2012 #5
    Hi, I was searching the forum for this. This video seems to say that this arrangement would run forever! Can anyone tell me where it would stop?

    [crackpot hoax link deleted]
    Last edited by a moderator: Dec 15, 2012
  7. Dec 15, 2012 #6
    My one guess is that the magnets demagnetize after sometime. But even then you can run it for a long time! Also, does the time a magnet get demagnetized related to the amount of energy obtained from a coil cutting its magnetic field?

    In other words, would a magnet whose field has not been come in presence of another magnet or a magnetic material be de-magnetized after a longer time?
  8. Dec 15, 2012 #7
    Okay, thank you all for answering. :smile:

    To clarify, if the magnet has potential energy, when does it lose its potential energy? Maybe when you use the magnet many many times over and over? At that point, will the magnet no longer be magnetic since all of its potential energy has been transformed into another form of energy?

    On a side note, is the universe itself not one giant perpetual-motion machine?
  9. Dec 15, 2012 #8
    Jay, If something looks to good to be true..

    If this guy has a monopole in his possession, let alone one that large, a lot of people will be really interested in meeting him. There's probably a battery in the base of the block or something. You'll notice that he:

    1. Never shows you what's under the block.
    2. Moves both hands off the screen when moving the meter leads.
    3. Never shows the machine 'not work' with the magnet removed.
  10. Dec 15, 2012 #9
    When you hold something above the ground and drop it, does the earth "lose" potential energy? If you drop the ball over and over will the earth eventually run out of gravity?

    No. Every time work is done, some is lost and becomes useless. Eventually, barring any other failure mode (big crunch, rip, etc), all the energy will eventually be uniform and thus useless.
  11. Dec 15, 2012 #10
    But the kinetic energy from two magnets slamming together is much greater than that required to pull it apart, if done properly, no?
    Can't magnets demagnetize after many uses? If not, how do they ever demagnetize?
    Last edited: Dec 15, 2012
  12. Dec 15, 2012 #11


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    Nope. The energy required to separate two magnets will always be equal to (or greater than) the energy with which they will slam together if released.

    There ain't no such thing as a free lunch.
  13. Dec 15, 2012 #12
    No. If you think this is the case, what example are you considering?

    They demagnetize because the atoms come out of alignment. This takes a long time if you aren't smacking things into them or subjecting them to a lot of heat. They can be put back into alignment easily enough as well.
  14. Dec 15, 2012 #13


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    Staff: Mentor

    Question has been answered and we don't discuss crackpottery here, even to debunk it. Thread locked.
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