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Dropping a magnet through the moon

  1. Apr 17, 2015 #1
    Let's say we built a tunnel through the (arbitrary) center of the moon, and lined the surfaces of the walls with millions of loops of copper wire. If we dropped a massive magnet in through the moon, would it produce a substantial amount of current due to the magnetic field passing through the wire, and keep going back and forth due to gravity? And would it be worth it?
  2. jcsd
  3. Apr 17, 2015 #2


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    If the coil ends were open-circuited, then there would be no losses and the magnet would keep oscillating between the surfaces of the moon.

    If the coil ends were connected to some load resistance (like a generator), then the back-emf would slow down the passage of the magnet on each oscillation on each pass, with the end result of the magnet stationary in the middle of the coil at the center of the moon, and you have extracted an amount of energy from the coil corresponding to the initial Gravitational Potential Energy of the magnet when released at the surface of the moon (minus inefficiencies).

    Makes sense?
  4. Apr 17, 2015 #3


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    You might produce a current, but the magnet will not come out to the same distance again. It will simply get stuck in the middle relatively fast.
  5. Apr 17, 2015 #4


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