If I were to take a impermeable globular ballon, say 50 meters in diameter and force it into the ocean to a depth at which the density of the balloon became too heavy for the bouyant force to support it, then it would sink. If it sank deep enough, the water pressure surrounding the balloon could eventually squeeze the ballon to a diameter of 1 meter. Of course, the balloon would be much more dense because the air trapped inside the ballon is now occupying a much smaller space.

But if I reversed the process and somehow managed to resurface the balloon from the bottom of the ocean, as the water pressure decreased would the balloon expand? Since the air has no where to go, does it "re-inflate" the balloon?

When I pull the balloon from the ocean, is it again 50 meters in diameter?

Cable out again? ;)

But if I reversed the process and somehow managed to resurface the balloon from the bottom of the ocean, as the water pressure decreased would the balloon expand? Since the air has no where to go, does it "re-inflate" the balloon?

When I pull the balloon from the ocean, is it again 50 meters in diameter?Yes.

Scuba divers actually have to be aware of this effect as they surface. They surface slowly (the rule is to go more slowly than your air bubbles) and release air from their lungs. Surfacing more rapidly or holding your breath you can damage your lungs.

~Raithere

If I were to take a impermeable globular ballon, say 50 meters in diameter and force it into the ocean to a depth at which the density of the balloon became too heavy for the bouyant force to support it, then it would sink. If it sank deep enough, the water pressure surrounding the balloon could eventually squeeze the ballon to a diameter of 1 meter. Of course, the balloon would be much more dense because the air trapped inside the ballon is now occupying a much smaller space.

But if I reversed the process and somehow managed to resurface the balloon from the bottom of the ocean, as the water pressure decreased would the balloon expand? Since the air has no where to go, does it "re-inflate" the balloon?

When I pull the balloon from the ocean, is it again 50 meters in diameter?
Yes, Yes.
Your baloon is imopermeable and I therefore cannot see how the water pressure can alter the fact that the balloon and air total density with respect to the density of water at the depth in question, itwill ever increase to be greater than that of water. Rememebr the balloon is impermeable. This being the case then the balloon would begin to rise as soon as the force holding it to the current depth is removed.

Yes.

Scuba divers actually have to be aware of this effect as they surface. They surface slowly (the rule is to go more slowly than your air bubbles) and release air from their lungs. Surfacing more rapidly or holding your breath you can damage your lungs.

~Raithere

It is more serious than that. Bubbles forming in the blood stream causes heart failure. The "Bends" are potenitally lethal.

It is more serious than that. Bubbles forming in the blood stream causes heart failure. The "Bends" are potenitally lethal.While also an effect of compression and decompression the bends works a bit differently.

Under pressure nitrogen dissolves in the body's fluids. As the body decompresses the dissolved nitrogen is released just like carbon dioxide is released when you open (and decompress) a can of pop. Bubbles in the blood stream are extremely painful and dangerous. Typically it's not a major concern though unless you are diving quite deep or for long periods of time. Recreation divers rarely suffer from it though it's always best to be careful.

The effect I was referring to is more common and is caused by the same mechanism as in sevenblu's experiment. Compressed air in the lungs expands as the pressure drops and can cause the lungs to hyper-inflate causing ruptures and hemorrhage.

Interestingly free divers don't need to worry about either effect even though they have gone as deep as 170m. This is because they only have one breath-full of air. The problems occur when you breathe air in a compressed state.

~Raithere

While also an effect of compression and decompression the bends works a bit differently.

Under pressure nitrogen dissolves in the body's fluids. As the body decompresses the dissolved nitrogen is released just like carbon dioxide is released when you open (and decompress) a can of pop. Bubbles in the blood stream are extremely painful and dangerous. Typically it's not a major concern though unless you are diving quite deep or for long periods of time. Recreation divers rarely suffer from it though it's always best to be careful.

The effect I was referring to is more common and is caused by the same mechanism as in sevenblu's experiment. Compressed air in the lungs expands as the pressure drops and can cause the lungs to hyper-inflate causing ruptures and hemorrhage.

Interestingly free divers don't need to worry about either effect even though they have gone as deep as 170m. This is because they only have one breath-full of air. The problems occur when you breathe air in a compressed state.

~Raithere

Full agreement.

Ok, honest answer to sevenblu question. Air won't work, it never would get dense enough to 'sink'. In order for that to happen, the density of the gas in the balloon would need to be greater than that of the water.

However, carbon dioxide would work. At 14.7 psia and 70 F, CO2 is a gas, so you could fill a balloon with it.

As you forced the balloon down to the depths of the ocean, the first thing you'd notice is the ballon shrinking as pressure increased. You might also notice the gas inside getting hotter. In effect, you're doing work on the ballon by compressing it - energy is being added to the gas inside the balloon and as a result, it gets hotter.

This doesn't make for a particularly interesting example, but if we assume the balloon doesn't have any insulation, then we'll find there is heat transfered from the hot gas to the relatively cool ocean. Lets assume the ocean is 70 F all the way down, and is fresh water instead of salt water, just for simplicity. (I don't have a computer database for salt water unfortunately) Lets also assume we push the balloon down slowly enough that the gas in the balloon has time to cool off all the way down such that it stays at 70 F. We might stop periodically in order for the gas to cool off.

At a depth of roughly 2000 feet, the carbon dioxide is going to be at a pressure of 838 psi, at which point we'll need to stop and watch the balloon contract rather suddenly. Its at this point, the gas changes to a liquid. It condenses as it cools on the inner surface of the balloon, liquifies, and the balloon shrinks untill it is completely filled with liquid.

But the balloon won't sink still, because the density isn't high enough, so we push the balloon down farther. As we descend into the dark depths of the ocean, the balloon continues to shrink and get more dense. Water is relatively incompressible, but CO2, even as a liquid, will continue to become more and more dense.

Eventually, we'll get to a point where the carbon dioxide actually gets as dense as the water. This happens at a pressure of roughly 5000 - 5500 psi or a depth of roughly 12,000 feet. If at that point, we release the balloon, the CO2 balloon will actually sink, becoming more and more dense as it descends.

As we turn this situation around, the exact opposite will occur, assuming heat transfer and everything else occurs just as before. The process of ascending is identical to the process of descending, but with the balloon getting cooler as it rises, and heat going into the gas. At a depth of 2000 feet we'll see the liquid boil on the relatively 'hot' surface of the inside of the balloon. When it finally gets to the surface, the balloon will be back exactly as it started. Again, assuming the heat transfer is the same as before.

thank you so much, now I can finally sleep.

Ok, honest answer to sevenblu question. Air won't work, it never would get dense enough to 'sink'.

Depending on the mass and volume of the balloon envelope, of course!
(I'm feeling pedantic today :) )

(I'm feeling pedantic today :) )

lol well, actually I took a look at some combination of pressure and temperature that might give you a density of air that's as high as water. Even at 100,000 psi, water is 10% more dense. That's a water depth of over 200,000 feet, and there's no ocean that deep.. oh wait, I hear Jules Verne found a way to the center of the earth ... perhaps if we fill up his hole with water, we might find.... nah, never mind.

Note that at that pressure, temperature doesn't have a very strong affect on density, its far from an ideal gas. :p