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Dec16-12, 07:57 PM
P: 22,296
Quote Quote by nhmllr View Post
Okay, let's say my arm was perfectly efficient. Or let's say that the block is a magnet that we suspend on top of a perfectly efficient electro magnet that strengthens and weakens in it's field, causing the block to move up and down. Basically what I'm saying is, if there are no inefficiencies, where does the energy go?
If you replace your arm with a spring, the energy just keeps bouncing back and forth between kinetic and two different kinds of potential energy.

But your arm, like a hydraulic lift, is not capable of absorbing and storing mechanical energy. So the act of lowering the object is always just a loss. Even if 100% efficient, it would only be a 1-way lifting device.