The first law of thermodynamics, an expression of the principle of conservation of energy, states that energy can be transformed (changed from one form to another), but cannot be created or destroyed.
The first law of pigs feet, an expression of the principle of conservation of pigs feet, states that pigs feet can be transformed (changed from one form to another), but pigs feet cannot be created or destroyed.
you cannot create or destroy anything.
you can only change something from one form to another.
the first law of paul , an expression of the principle of conservation of common sense , states that only energy is energy.
As a side note, compressing air is a thermal process. It generates heat, so it's less efficient than an elastic spring.
compressing a spring also generates heat.
so there both thermal processes.
To make it sink you have to use energy to compress the air. If you recover that while it floats back up then you can't recover it from the expansion of the bottle/piston. So you come out even at best.
that makes no sence , the expansion must happen before it floats back up.
ie.. the bottle will expand by itself.
the float at the bottom then rises due to buoyancy.
If you make it sink so deep that the pressure of the water compresses the air in the floater automatically and pushes it down further, then to bring it back up you have to expand that air. Doing that means lifting the column of water above it. So the deeper it goes the more energy you need to do a complete cycle.
first the video of the cartesian diver didnt have air inside it , it is just a piece of wood that has a metal paper clip attached at the bottom.
but since you mentioned compressing air lets suppose it was a inverted drinking glass , that had some air at the top.
you pressurize the bottle and the glass sinks , you compress it even more and the air at the top of the glass will compress even further , but as soon as you release the bottle or decompress the bottle the air at the top of the glass will expand on its own due to the decrease in water pressure as it rises to the surface.
so you only put energy in once , it is a small amount of energy compared to the amount of energy you can get back..
Doing that means lifting the column of water above it. So the deeper it goes the more energy you need to do a complete cycle.
if you were standing on the bottom of the ocean , and you held out your hand , all the water from your hand to the surface of the ocean and all the air from the surface of the ocean to outer space would be sitting on top of your hand.
but you wouldnt feel it.
and you could easily lift your hand , because the pressure underneath your hand would be the same as that on top.
these guys can explain it in this video much better that I can
http://www.youtube.com/watch?v=j7EA1KRK7eI&feature=related .
