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Spinning Objects

  1. May 19, 2012 #1
    I havnt taken physics in a while and cannot remember much. But i came here to see if an idea i had was possible. The idea is that if you were to spin a magnet in space(becasue from what i remember if you spin an object in space it continues non-stop(i have bad memory though)) you can use the spinning magnet like a hydro generator, to create limitless electrical energy. But first i want to know if you were to spin a magnet in space if(pt1) it will continue to spin non-stop and (pt2) it could be used like a hydro generator were it has coils around it to create electricity. Please answer this if possible.
  2. jcsd
  3. May 19, 2012 #2
    Whenever one extracts energy from a system, the energy must (Correction: come from somewhere). In this case, the magnet's spinning will slow down.
    Last edited: May 19, 2012
  4. May 19, 2012 #3
    Im a little slow,can you explain it a little more?
  5. May 19, 2012 #4
    So, basically, Conservation of Energy implies this energy must come from somewhere. The only place it could come from in this situation is the rotational kinetic energy of the magnet.
  6. May 19, 2012 #5
    Ok,i see now. Thank you.
  7. May 19, 2012 #6
    But if you take part of the gatherd energy to start it up again, it would only create the same amount of electricity used to respin it again?
  8. May 19, 2012 #7
    Actually, due to friction, you'd get less energy back.
  9. May 19, 2012 #8
    But were would the energy from friction go? I know space is cold so the energy from friction would create heat but be gone from the cold of space.
  10. May 19, 2012 #9


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    Staff: Mentor

    Both motors and generators are basically the same device: rotating electromagnets that convert energy between electrical and mechanical. When you apply electricity to a motor, it rotates. If you want it to produce more torque, it will need more electricity. Generators work the same way: if you want to extract more electrical energy, they will produce a stronger magnetic field, which will require more input torque to counteract.

    It surprises me that while most people are aware of how motors work (and don't expect a violation of conservation of energy), this question is very common when it comes to generators.
  11. May 19, 2012 #10


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    Science Advisor
    Gold Member

    It would be like using an electric motor to power an electric generator to power the electric motor. It doesnt work. Extracting energy from a motor creates a braking torque on the motor. Drawing energy from a generator also creates a breaking torque on the generator [its just a reverse wired electric motor].
  12. May 20, 2012 #11
    It would just get dissipated, and while the heat wouldn't have much of an effect on the surroundings, this doesn't affect how much heat energy was released.
  13. May 20, 2012 #12


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    Staff: Mentor

    The energy is not being dissipated as heat, it is being converted from mechanical (kinetic) to electrical.
  14. May 20, 2012 #13
    And the quote I was replying to was asking where the energy from the friction would go.
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