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 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!