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Permanent magnets

  1. May 24, 2017 #1
    First off, I am new here, so please don't tear me apart too hard if I miss or misinterpret something, I'll cotton on eventually :D

    As I understand it, when a permanent magnet repels an oppositely charged object, such as another oppositely charged permanent magnet, no energy is technically being used for the magnets to repel each other, as it is the same principle as putting an apple on a table. The stiffness of the table is counteracting the force of gravity's force on the apple, and that is why the table doesn't just collapse. The stiffness is from the electromagnetic interactions of the atoms making up the table, so in the end it is the EM force counteracting the gravitational force. The magnets repelling each other is caused by electromagnetic interactions.

    In this case, if I were to mount negatively charged permanent magnets onto the blades of a fan, and rotate them using the repulsion of a positively charged permanent magnet, then use said fan to power a dynamo that generated electricity, where would the electrical energy be coming from? Energy cannot be created (or destroyed for that matter) so where is it coming from?

    Yes, the magnets may eventually lose their magnetism due to surrounding heat and such destabilizing them, but don't magnets still work at absolute zero? In a vacuum environment at absolute zero with no outside forces that can destabilize the magnets at that moment (the friction of the fan turning would generate heat, which would radiate to the magnet and perhaps destabilize it over time) the magnets would still repel, yes? At absolute zero, in a vacuum, there isn't much energy going around that the magnet can readily store and convert to repel it's opposite. As far as I am aware there is no energy change in a magnet anyway. Where is it coming from!?
  2. jcsd
  3. May 24, 2017 #2


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    That doesn't work and videos on YouTube that appear to show the fan rotating are _all_ fake.

    Magnetic force is a conservative force. Read the first paragraph of this..


    If the fan were to rotate that would be the equivalent of a particle (magnet) returning to its starting position once per revolution (eg travelling around a closed loop) so no net work is done. No work means nothing to overcome friction so it cannot rotate.
  4. May 24, 2017 #3


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    PS Welcome to the forum.
  5. May 26, 2017 #4
    Note that:
    A positively charged object ATTRACTS a negatively charged object.
    A positively charged object REPELS a positively charged object.
    A negatively charged object REPELS a negatively charged object.

    similarly for magnetism:
    North and south poles attract each other.
    A north pole repels a north pole, and a south pole repels a south pole.

    Ever try to pull two magnets stuck together apart?
    You have to do work to do that.
    The work can be recuperated by moving the magnets back together again.
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