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This video lists a number of perpetual motion machines that have been proposed throughout history:

These are all mechanical machines, which use gravity to operate, i.e, they are a way to transform the force of gravity into energy, and do not need batteries or motors. Since I think that those machines are not really perpetual motion ones, can they turn for hundreds of years or will it stop just after some minutes?

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They will stop when the batteries run out - each one has a hidden pump or motor, that's all. –  Nathaniel Oct 2 '13 at 13:44
    
@Nathaniel Those machines do not violate the current laws of physics, instead, they try to use the force of gravity. –  user29727 Oct 2 '13 at 17:47
    
Trust me, the ones in that video have hidden motors. (Apart from the perpetual train, where if you watch the weight rather than the slope it's on, you'll see it just rolls downhill for a bit then stops.) The thing that all those proposed machines have in common is that they don't work. Friction very rapidly stops them from turning. –  Nathaniel Oct 3 '13 at 2:06
    
@Nathaniel What about Jacob Leupold’s Overbalanced Wheel and Boyle's Self-Flowing Flask, isn't it a way to convert the force of gravity into energy? –  user29727 Oct 3 '13 at 12:27
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you generate $mgh$ of energy for each weight you move from the top to the bottom, but you pay $mgh$ to get it back to the top again. So the total is $0$, always. It doesn't matter how they're connected or how they move, this will always be true. The impossibility of ever getting a non-zero amount of energy from such a machine is one of the most fundamental laws of physics there is. –  Nathaniel Oct 5 '13 at 14:56
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1 Answer 1

Wikipedia describes Perpetual motion as motion that continues indefinitely without any external source of energy. This is impossible in practice because of friction and other sources of energy loss.

Of course, this is practically impossible since you can never fully eliminate the frictional forces. Although we say it’s impossible, people still like to come up with ideas. Perpetual motion machines are sort of like playing the lottery. People think they have a much higher chance of winning than their actual chance of winning.

Perpetual motion describes motion that continues indefinitely without any external source of energy is impossible in practice because of friction and other sources of energy loss. It violates the first or second law of thermodynamics.

See this detailed explanation at wired.com with a kind of experimentation.

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Those machines do not violate the current laws of physics, instead, they try to use the force of gravity. And we can eliminate frictional forces with super-fluids. –  user29727 Oct 2 '13 at 17:48
    
instead, they try to use the force of gravity Force does not equal energy. You need room to do work. That is the fundamental law they're trying to break. And we can eliminate frictional forces with super-fluids.. ELIMINATE? Tell me again, how we can eliminate friction... –  Cruncher Jan 6 at 16:15
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