I know that perpetual motion cannot exist. I'm just looking for the flaw in this system:
0) Construct a very tall silo of water (ex: 6 feet in diameter, 1000 feet tall).
1) place a very heavy, but buoyant object in the bottom of the silo (lifting the object to the top of the silo)
2) push the object off the side of the silo, and allow it to turn a turbine or something.
3) put the object back in the bottom of the silo; repeat.
It seems like there is an incredible amount of "free" energy to be harnessed from allowing the buoyant object to float to the top of the silo, increasing it's potential energy. Where is this energy expended that would invalidate the premise of this machine?