QUOTE(tansqrx @ Aug 22 2007, 09:05 PM)

You are on the hunt for the age old myth of the perpetual motion machine. The bottom line is it does not exist.
http://en.wikipedia.org/wiki/Perpetual_motion. It has been tried so many times that the US patent office will flatly refuse any application that is a perpetual motion machine.
The one thing that most people miss in this argument is efficiency. In other words, in the real world there is no such thing as 100% efficiency or perfect transfer of work (power) from one place to another. Take the turbine example. As the turbine is spinning you also have friction in the bearings, wind drag, and heat produced. All of this equals energy being lost in the system and a dropped efficiency. Even if the system is of 99%+ efficiency, that 1% will eventually bring the whole system to a stop.
Yup, that pretty much sums it up. The turbine system you talked about converts gravitational potential energy (the water being higher) to kinetic energy (the water falling and turning the turbine) to electical energy. Assuming that perpetual motion was possible (namely no friction and so on), you'd have no energy left to use at the end. As soon as you start tapping energy from it then it can't shift as much water back to the top to give it more energy, and so on.
One idea that has left me pondering is magnetism, however. If you attached magnets to a turbine such that they span as the turbine did, and had opposing pole magnets on opposite sides (so effectively you're spinning one large magnet), could you use that to, say, push a metal object up a tube against another turbine, and when the poles attracted it instead of pushing it away cause it to drop, generating more energy? As the motion wouldn't be directly opposing the motion of the first turbine (perhaps creating a little more friction as the axle is marginally tilted) could you use the same source to generate more energy?
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