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Consider a single isolated rotating mass (for example planet), is it possible to extract energy out of its rotation? If yes, how could that theoretically be achieved?

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3 Answers 3

Attach magnets, bring wires close, enjoy while it lasts. The changing magnetic field would induce currents in the wires, hence you could extract out energy from the rotating system.

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How would you hold stator in place to make it work? –  Ardath Apr 22 at 22:20

Caution: I have not worked this out rigorously, and I'm not entirely convinced that it works (or even that the problem is solvable). Comments appreciated.

The answers here all have the disadvantage that they fundamentally require large amounts of mass not in the same non-inertial frame to work properly. But what if there simply was no such mass? In other words, what if the entire universe consisted of our rotating orb, and us, on it. How would one extract the energy from the orb?

It's pretty obvious you have to do this by exploiting fictitious forces. One way is to coil a string around a wheel, and place a large mass on one end of the string - as the mass flies outward, it will spin the wheel up, giving us energy. The disadvantages are that we lose the mass permanently (it costs the same amount of energy to get it back), and it won't work in the presence of a gravitational field stronger than the fictitious outward force.

That's ok though, because there are other fictitious forces. To make this a bit easier to visualize, suppose we were on a merry-go-round, spinning counter-clockwise. Sitting at the center, facing outwards, I push a marble. The coriolis force takes over and the marble veers to the right. Intuitively, this happens because doing otherwise would require the marble to speed up. The marble needs to keep the same kinetic energy as it had before from an intertial reference frame, so it veers to the right. If we resist that motion, we ought to be able to extract energy, and then bring the marble back down to $r=0$.

At this point the details aren't too hard to work out. Launch a bar magnet into the air (the energy for this will be re-gained, in part, when the magnet falls), and induce drag on longitudinal motion with some wires nearby (from which electricity is extracted). Repeat. If you set this up all long the equator, you shouldn't even need to worry about re-positioning the magnet.

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A little hard to do, but say..

  1. You build a sun room on the surface of the sun.
  2. You tether the axle of a bicycle wheel sitting on the surface of the earth to your sun room on the surface of the sun.
  3. As the earth turns, the bicycle wheel turns. It stays in place as it is tethered to the sun.

Now - you can extract energy from the turning of the bicycle wheel.

Must be an easier way?

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Isolated mass means that there is no other massive object nearby. –  Ardath Apr 22 at 22:24

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