The density of sea water is slightly greater than 1000 kg/m3 and the
acceleration due to gravity is slightly less than 10 m/s2. So a column
of seawater 10 m tall and 1 m2 at the base has a mass of slightly
greater than 10 000 kg and a weight (W = mg) of approximately 100 000 N
or 100 kN. That means the pressure at the bottom of the column (P = F/A)
is approximately 100 kPa, which is very close to the "standard
atmospheric pressure" value (101.325 kPa) used by the World Meteorology
Organization and the American Meteorological Society.
More specifically, the average density of seawater is 1027 kg/m3
according to the University Corporation of Atmospheric Research (UCAR).
Others claim values ranging from 1020 kg/m3 to 1030 kg/m3. The value
used in the past for the "standard acceleration due to gravity, g_n" is
9.80665 m/s2. The product of those two "standard" values is 10 071.429
55 kg/m3 making the pressure added by a 10 m column of seawater to be
100.714 295 5 kPa. This is even closer to the "standard atmospheric
pressure" stated above.
This matter of course was of interest to me in my previous work in
physics but it was **especially** important to me when I operated
submarines during my navy career. A bit of trivia: submarines made of
steel are more compressible than seawater so a neutrally buoyant
submarine becomes negatively buoyant if it dives to greater depth. Water
must be pumped out of internal variable ballast tanks then to restore
neutral buoyancy. The relative compression factor is classified; I will
not give you a value.
Jim
Harry Wyeth wrote:
I have always found it interesting--as a certified SCUBA diver--that Th
according to someone's law of pressure (Boyle? Dalton? Kilroy's?
Someone else?), pressure on the body underwater doubles at 33 feet.
That's 10 m, of course. That is, at 10 m there is 2x atmospheric
pressure, and that there is 3x at 20 m, etc.
I have always wondered just why this is. Why at 10 m, and not, say,
11.5, or something else? Anyone know? Just a coincidence?
HARRY WYETH
--
James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
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