Diving 107: Scuba Diving Underwater Physics
33.03 feet sea water = 1 Atmosphere pressure = 14.7 psi
34.03 feet fresh water = 1 Atmosphere pressure = 14.7 psi
PV=nRT
P=T/V or V=T/P or T=PV
P = pressure in psi
V = volume in ft
3
n = moles of gas (1 mole = 6.022 x 10
23
atoms)
R = gas constant 10.7316 psi ft
3
/ lbmol °R
T = temperature in Rankine (°R) = °F + 459.6
P
guage
= 14.7psi x [depth of sea water] / 33.03 feet sea water
P
absolute
= 14.7 + (14.7psi x [depth of sea water] / 33.03 feet sea water)
Sea water weighs 64.58 lbs/ft
3
pr 8.6213 lbs/gallon Specific gravity = 1.035
Fresh water weighs 62.4 lbs/ft
3
or 8.3303 lbs/gallon Specific gravity = 1.000
Bouyant Force (Archemedes Principle):
F
buoyant
= W
in air
- W
in water
= dgv
F
buoyant
is the buoyant force
W
in air
also known as dry weight
W
in water
is weight in water [remember that negative numbers are positively buoyant]
d is the density of the liquid [salt water is 64.58 lbs/ft
3
and fresh water is 62.4 lbs/ft
3
]
g is the gravitational acceleration 32.37 ft/sec
2
(normally written as 1 in the equation i.e. 1 gravity)
v is the volume of the object in cubic feet (ft
3
)
For calculating the tissue depth for Haldanean decompression M-values, an easy to remember formula is:
D
final
=[1-2
-(t/h)
]*D
actual
D
final
= the final tissue depth
D
actual
= actual dive depth
t = time underwater
h = halftime compartment
I have written a function for the R language which calculates the EAD, PO2 and working depth for any FO2 breathing gas blend.
You can find my simple function here:
http://quashnick.net/scuba/university/Nitrox_for_R.txt
A better option is to use the R-Project (http://r-project.org) Package called scuba. You can find it here:
http://cran.r-project.org/src/contrib/Descriptions/scuba.html
Links
http://physics.itsbaxter.com/links.html
- Good site for more information on the physics of scuba diving.
Document Source:
http://Quashnick.net/scuba/university/diving107.html
Design and Content:
Stephen Quashnick