I was just swimming with a floating board for the pool, and came up with a thought. What would happen if you had two tubes one filled with air, and the other one filled with water. If you could somehow get an object less than half the density of water to fall down the tube with the air and go to the bottom of the other tube to displace water, couldn't the buoyant force exceed -1 times the force of gravity on the object? I posted an image on Wikimedia to illustrate this: http://commons.wikimedia.org/wiki/I...use_of_Negative_Buoyancy_to_run_a_turbine.gif If it could run a turbine with this, it would clearly violate the law of conservation of energy. But apparently, a nonconservative force is involved (i.e. gravity). Clearly, there would be a better mechanism for the "water lock" than a carousel, but this is what I came up with. So I need to know soon, WHERE is the catch (assuming all leakage problems are handled correctly)? Something doesn't make sense.