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Q & A: Water compressibility

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Q:
Due to the pressure at the bottom of the ocean is the water "thicker"? i.e. If you have 10 gallons of water at sea level would it still be 10 gallons at a mile or so under the surface? If not what would be the volume? I ask this because I was watching a show where they were testing a deep-sea exploration capsule. They sent it down empty and it leaked. When they opened it on the deck of the ship again water shot across the deck for much longer than it should have taken to empty the container?
- Cameron Holland
Fargo ND
A:
Here's a table of water volumes at different temperatuers and pressures. Yes, water does in fact compress as you raise the pressure (no surprise here), but it doesn't compress by much.


temp F(C) 0 atm 500 a 1000 a 2000 a 3000 a
32 (0) 1.0000 0.9769 0.9566 0.9223 0.8954
68 (20) 1.0016 0.9804 0.9619 0.9312 0.9065
122 (50) 1.0128 0.9915 0.9732 0.9428 0.9193


A mile under water gives about 150 atmospheres of pressure, so that should be less than 1 percent compression, according to the table.
What you probably saw on the show was an effect of the trapped air in the leaky capsule rather than the water. The "empty" capsule was really full of air, and as water leaked into the capsule at high pressure, the air got squeezed into a tiny little space. When the capsule was brought back to the surface, the air expanded and pushed the water out, shooting it far across the deck for a longer time than if there was just water in the capsule.

Tom J. (w mike)

(republished on 08/02/06)

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