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I know there must be a reason this wouldn't work

  1. Jan 19, 2006 #1
    I was thinking about how gravity is used as an energy source, for instance, gravity pulling water over a wheely-thing produces hydroelectricity. I wondered if there was a way to perpetually use gravity as a continual source of energy without the normal catch -- water can only fall once before it has to be raised up again, and that raising up would nullify any benefits of getting the water running through such a continuous loop.
    So why not just harness the energy generated by a continuously falling object? This may not be kosher science-speak, but isn't it safe to say that when you stand on the ground, you're continuously falling into the ground, only resisting that pull by means of your muscles exerting energy in the opposite direction?
    I recently learned of a material which can take advantage of such physical force and convert it to electricity: http://www.scienceblog.com/cms/material_reveals_unexpected_intriguing_behavior_9804 [Broken]
    To sum up, why not just place a plate of this material under a heavy object such as a house? Wouldn't the weight of the house generate a fair amount of electricity?
    I don't see how this couldn't have been thought of before, so I'm sure there's some major fallacy in my understanding that makes this impossible or impractical. Otherwise we would have perpetual energy sources!
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jan 19, 2006 #2


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    Only something in orbit is continuously falling toward the ground. In the case of a house or whatever, there is gravity continuously pulling on it, but it can't fall because the ground is in the way. Once it settles onto the generating device, no further work can be done unless it is raised and dropped again.
  4. Jan 19, 2006 #3
    Granted, but the article I linked to said "squeezing" (a constant force) could generate electricity. I assumed that meant constant pressure on the molecular structure was generating energy somehow.
  5. Jan 19, 2006 #4
    Gravity causes a mass to exert a downward force, but force is not the same thing as energy. To transform this force into energy you need a displacement of the mass in question. Unfortunately there is only so far you can go downward before you hit the ground, after which you have to raise the mass again to produce more energy, and this consumes exactly the energy you had initially produced. No free lunch.
  6. Jan 19, 2006 #5
    "Squeezing" something is a similar thing. A force is applied over a distance, even when this distance is extremely short. Squeezing a spring using a force will visibly store energy in the spring. This is not so visible when you squeeze a piezoelectric crystal (like those used in lighters) but some type of action within the molecular matrix does cause electrons to move in response. But then it stops because there's also a limit as to how much action can be produced until you re-apply the force and re-displace some material again. Still, once the force has displaced what it could displace and has produced the energy it could, the system stabilizes and no further energy comes out of it.
  7. Jan 20, 2006 #6
    Gotcha. Thanks for your responses!
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