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A kind of strange Underwater Air Bubble question


CS_SJ
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Hello,

Something I’ve wondered about is those amazing air bubbles that are sometimes found in underwater caves. In particular, I was wondering how the depth of the water does or does not affects them.

In my Figure 1 example, the water is 50 feet deep and air bubble in the cave has 3 feet of air from the top of the cave to the water, and the air pressure in the bubble is the same as sea level.

Well, what would happen if the same cave was 1000 feet deep? (see Figure 2.) Would the bubble still have 3 feet of air from the top of cave to the water? Or would the tremendous weight of the water make the bubble much smaller like just 3 inches tall or something? And what about the air pressure? Would the air be super compressed?

If this is the wrong place to ask this question, I apologize in advance, and if you could direct me where I could get an answer for this, I would appreciate it.

Thank you,

- SJ

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10 minutes ago, CS_SJ said:

In my Figure 1 example, the water is 50 feet deep and air bubble in the cave has 3 feet of air from the top of the cave to the water, and the air pressure in the bubble is the same as sea level.

No, that’s not correct.

The pressure under water will be the atmospheric pressure plus the pressure from the weight of the water, pgh (p is the density)

You add 1 atmosphere with a column of water of about 10.3 meters, or ~33 feet.

Water is almost incompressible, so you add another atmosphere for each 33 feet.

 

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  • 2 months later...

Yup, pressure squeezes air pockets.

As a kid, I remember playing with a tiny one-inch frogman free gift from a box of Sugar Puffs, you popped him in a glass lemonade bottle full of water, then made him go up and down by screwing the bottle cap up and down.

He was designed to have a tiny bubble of air trapped in his goggles and we could see the bubble shrinking as we screwed the cap, making him dramatically sink to the bottom of the bottle through loss of buoyancy. 

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