my idea , using gravity and buyancy... Please read

[Tom Watkin]

As you can see it uses buoyany at the left hand side and gravity on the right

The problem being, how can we reintroduce the ball(s) back into the water ? without, leaking too much water, or taking too much power to do so?

[zerotensor]

The problem being, how can we reintroduce the ball(s) back into the water ? without, leaking too much water, or taking too much power to do so?

That is the problem.  The way buoyancy works is that the pressure at the bottom of the float is greater than at the top of the float.  In order to replace the float at the bottom of the column, you would have to displace an equal volume of water.  The weight of water displaced by the float will be larger than the mass of the float itself (otherwise it wouldn't float).  Not only that, but the entire column of water above the float would have to be displaced.  The gravitational potential energy gained by the float as it rises in the column is not enough to displace the entire column of water when the loop is closed.

Have you ever tried to dive to the bottom of a pool while holding on to an inflated ball?  It's a lot of work.  The amount of work you could get out of the ball by releasing it is at best equal, and in reality substantially less, than the work you did to get it down there.  And it doesn't matter if you dive down with the ball from the surface, or push the ball through an orifice at the bottom of the pool; the work you do is the same.

As for the coils,  remember that the emf generated is due to the time-rate change of the flux, a current will arise to create a magnetic field to oppose that change.  The coils will create a magnetic field which opposes the motion of the magnet, slowing it down, and thereby diminishing the time-rate change of flux.  The energy extracted will always be less than the potential energy (either gravitational or buoyant) input to the system.

Of course, if you were to attach the black box at the bottom to "the very wheelwork of nature", you could do this all day long...

[zerotensor]

I thought I had a bright idea that would make this work, involving a clever valve and airlock assembly, but after a few minutes of thought I have convinced myself that it wouldn't work.

[Haliburton]

I thought about the same thing when i was using magnets.  its more harder to introduce it back into the energy source.  Magnets push it up. gravity pulls it down.  now try to get it back on the magnet

[aleks]

You could try to disintegrate the buoy into small particles and have them leak through a porous membrane on the bottom of the water tank. If pores are small enough, the water's surface tension will not allow water to leak down while it will probably allow particles to leak and go up. OK, it's probably cheating (you still have to put an energy into disintegration and make sure particles auto-assemble into a buoy when they enter the water), but that's only an idea. Disintegration could be also accomplished when then buoy falls down. Anyway, law of energy conservation won't allow this to happen, and the process will stop when particles will try to overcome the water's surface tension barrier.

It's cool we have entered 'nano' physics world, so theoretically we can create "smart" materials which attract to each other in the water and repel from each other in the vacuum/air.