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Gravity used to produce Electrical current?

  1. May 5, 2012 #1
    Hi, I'm not a physicist or anything so my question here can be silly, please take it easy on me and tell me -if so- why wouldn't this work.

    My thought is as follows:

    We need a pipe, water, a vacuum vessel that can expand and contract by mechanical means, copper wires, and a magnet.

    First hold the pipe vertically and fill it with water, put the copper wires around the pipe in coils. Attach the magnet to the vacuum vessel, and put it in the pipe.

    Now, from basic physics, if the vaccum vessel has less density than the water it will flow, and if it has a higher one it will drown.

    Assuming when it's fully contracted it has higher density than water, it will drown and the magnet will move throgh the coil and produce current.

    Once it hits the bottom, the vessel expands, hence the density is lowered -greater volume means less density, right?-. Again assuming it has less density than water when it's fully contracted, then it will flow up and the magnet will move throgh the coil and produce current again. And it expandes again when it reaches the top, repeating the whole mechanism again.

    The longer the pipe the more electricity generated -since we have more wires cutting the magnetic field-, and at a certain length, this set is "supposed" to produce energy more than it consumes to expand and contract the vessel.

    I know, it might not be financially feasable, but I'm talking about the concept. And again, I'm not a physicist, so I may have made a completely silly mistake here.
    Your thoghts please.
  2. jcsd
  3. May 5, 2012 #2


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    NOTHING will produce more energy than it uses

    this thread is touching on a subject that is not allowed on this forum
    I suggest you read the posting rules before thinking of taking this discussion any further :)

  4. May 5, 2012 #3
    Oh sorry didn't know this subject was not allowed, if it's really against the rules then a mod should close this thread..

    Again sorry for breaking any rules :)
  5. May 5, 2012 #4


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    no probs :)

    just be aware that any subject to do with free energy, perpetual motion machines and anything in that area is not allowed
    mainly because its all B.S. lol and lacks any scientific credibility

    other than that
    welcome to the Physics Forums and read a few threads on things that do get discussed in many branches of science :)
    you may find some interesting stuff

  6. May 5, 2012 #5
    I'm not sure I agree with a policy of shutting these threads down on sight; it's often interesting and instructive to consider /why/ a given perpetual motion machine won't work.

    In this case, unfortunately, the work required to expand the vessel against water pressure at the bottom of the tube will always be greater than the electrical energy it generates in its travels. You can try to make the tube really long so as to generate a lot of electrical energy in one pass, but that just increases the water pressure at the bottom of the tube, since a larger column of water is bearing down on it, making it even harder to expand the vessel at the bottom.
  7. May 5, 2012 #6


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    the why is very simple, they break the laws of physics - period!

    there doesnt need to be any discussion as it is pointless
    anyway thats the rules of those that run the forum

  8. May 5, 2012 #7
    I feel guilty to discuss this further after I knew it's against the rules, but I can't help it ;p.

    What if we replaced the expanding vessle with a hollow vessle that is connected to a pump via a hose.

    If we fill this vessle with water it will drown, once it reaches the bottom, the pump will empty the vessle via the whose -the water is extracted outside the whole set-, and it will float again.

    That problem is solved, but still why wouldn't this work? -since if it did, someone would have done it before :)-.
  9. May 5, 2012 #8


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    You need the energy to pump the water out as well. You use the pressure gradient for buoyancy, which means that when you change the contents of the tank you are working against the pressure, regardless of whether you generate energy on sinking or floating. So the net energy gain will always be zero minus losses, which is a net loss.
  10. May 5, 2012 #9
    If you want to do more than one cycle of this process, you have to remove the water from the vessel at the bottom, then lift that water up to the top and put it back in the vessel. The work expended to lift the water up that distance is larger than the energy you can extract from putting it in the vessel and letting it descend again.

    Fundamentally, you are generating power by extracting the gravitational potential energy that the vessel has at the top of the tube, and which it gives up as it descends the tube. But any mechanism for putting the vessel back in its original state at the top of the tube has to give it back the same amount of gravitational potential energy. So it costs at least as much energy to reset the system as you can extract from running it for one cycle.
  11. May 6, 2012 #10
    Wouldn't it be beneficial to the OP to explain to him exactly how/ which laws of physics are broken, as he obviously doesn't understand? I got the impression that he's asking for guidance here, and not actually claiming to have invented a perpetual motion device. I could see how one can learn a lot from this discussion, as OP's mind is already primed for information.
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