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Gravity > Perpetual Motion > Charging by Induction and energy

  1. Dec 2, 2004 #1
    So according to my common sense and logic and some disscussions I had with other people on IRC, theoretically in space if you had a exactly/perfectly spherical planet with a cylinderical hole through it, and you dropped something -a huge permanent magnet to be specific- through that hole, the thing would move up and down forever until some force is exerted on it, Correct ?
    Then right in the middle of this hole, we put some coils. When the magnet goes through this coils, it is going to create a EMF on the coils correct and according to Lenz law, there will be an electromagnetic friction. But if we remove the current as soon as it is created, there wont be a friction, thus the thing would just keep moving ?! If this were possible then it would be against the laws of thermodynamics, the second one if I recall them correctly, unless gravity is also a form of energy.

    So since this is not possible, where am I thinking wrong ? :rofl: :rofl:
  2. jcsd
  3. Dec 2, 2004 #2


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    All you need to do is to actually PERFORM this experiment yourself. You will realize that the moment you try to push a magnet through a coil, you will feel a RESISTANCE against it. This means that you have to apply a force to get the magnet into the coil - the force you apply gets larger as you try to move the magnet faster into the coil.

    Lenz's law is the result of the conservation of energy. The induced current in the coil, no matter how fast you "remove" it, will generate its own magnetic field to oppose the changing magnetic field flux from the magnet. This is inescapable.

  4. Dec 2, 2004 #3


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    I have no idea what you mean by "remove the current as soon as it is created" but (a) if the current fails to come into existence you can extract no usable energy from it in which case your scheme is a nonstarter and (b) if it does come into existence and you extract usable energy then it had to have come from the magnet-planet system and that energy loss will zap your perpetual motion machine out of existence.
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