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Q:
How deep do you have to go to get 80 bar
- Catherine Considine
A:
Hi Catherine,
The pressure in a fluid at a depth h is due to the weight of all
the fluid on top, plus the pressure of the earth's atmosphere on top of
that fluid. The pressure is equal to rho*g*h + 1 atmosphere, where rho
is the density of the fluid, and g is Newton's gravitational constant
(9.8 meters/sec**2). Be sure the units all match up (I recommend SI
units. rho is in kilograms/cubic meter, and h is in meters, and you'll
get the pressure in Pascals. But I'll express the results in the usual,
clumsy units below).
80 bars is about 79 atmospheres. Accounting for the 1 atmosphere
due to the atmosphere, you only need 78 from the fluid. In seawater
(you'll need the ocean for this I think), the pressure increase is
about one atmosphere for every 10 meters. So you need to go down 780
meters below the surface, or about half a mile. You'll need more depth
in fresh water because it is less dense (no salt in it).
Tom
(published on 10/22/2007)
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