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Physics/buoyancy force


QUESTION: Dear Sir ,  Can we  consume buoyancy force from water as a energy.

ANSWER: Sure I've heard of an idea for using bubbles of gasses emitted from geothermal vents in an "underwater waterwheel" before.  This would work.  It is not, however, a fundamental source of energy in and of itself.  Something else has to actually submerge whatever you wish to use for the buoyant force, and that requires (natural or human-supplied) some source of energy.

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QUESTION: Dear sir,sir
         Thanks for your answer, i send a image  for  operation of  energy harvesting by gravity force and buoyancy . Can this system possible  to make energy. I need your technical advice. This system is my own idea.

Ah, yes, I've seen this design and variants on it in the past.  Just one example of a whole page devoted to it:  And here's another:  Also here:

Now, to your particular machine.  It's an excellent design, in theory, because you can clearly see that each side should rotate your chain counter-clockwise constantly.  It seems, if you look at it from a force perspective, that it should rotate counter-clockwise (as drawn).  Buckets on the left to pull down, buoyant buckets on the right to pull up...seems reasonable at first glance.  However, it turns out that the devil is in the (as usual) details.  You have (as drawn) 19 floats or buckets or whatever you call them.  You can just cancel the weights of the buckets going up and down on the left and right hand sides (whatever they gain from their weights in falling they lose in the reduction of the buoyant force going up, so that really doesn't matter).  So we can, for simplicity, go with massless buckets.  You have multiple buckets of volume V going up on the right hand side.  It looks like it should still work, but you have to consider the pressure at that depth.  Each bucket that goes up gains an energy = rho*V*g*h (that's the force*depth of the water), where rho is the water's density.  For every bucket coming out, you have to pull one in the bottom.  That's the problem.  If you assume, for simplicity, that each bucket has a cylindrical geometry with a top area A and a length L (volume V=A*L), then you have to fight a pressure force of rho*g*h*A to get it in.  The net buoyant force of each one, even if they're end-to-end so that the height h is equal to n*L where n is the number of them is rho*L*A*n*g = rho*h*A*g, which is exactly the force that the bottom bucket is fighting to get in against all that pressure.  Simply put, you're underestimating the pressure on your airlock at that depth.  Any loss whatsoever from friction stops the system.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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