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in this video at arround 0:47 they deliver the 'dry pots' to the under water lab, bellow the water and they seem to swim up into an opening where it is completly dry.. how is this dry, surly the water would fill into that void seeing as its under water ?

Sorry if this is such a basic quesiton !

http://www.youtube.com/watch?v=kuI7KFsKrBY&feature=player_embedded#!

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If you turn a glass upside down and put it in a sink full of water you'll find the air stays in the glass and stops the water filling the glass. This is exactly how the undersea lab works. The lab is sealed apart from the opening in the bottom, so the air inside it can't escape, and the trapped air keeps the water out.

The air has to be at the same pressure as the water (otherwise the water pressure would compress it and allow some water in) so the pressure is higher than on the surface. That's why the chaps in the lab have to open a valve on the barrels containing the towels before they can open them.

You have to be very sure there are no leaks in the undersea lab. Any leak would allow the air in the lab to leak out and bubble to the surface, and sea water would rush in to replace the leaked air.

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There are instabilities for glass in water which make it difficult to do if the glass tapers outward. You can do it more easily with an upside down coke bottle. –  Ron Maimon Jul 18 '12 at 3:04
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