Physics Review
Depth and Pressure
In this module you will review the relationship between depth and pressure.
This understanding is needed as a tool in subsequent pages.
 As a diver you are interested in depth,
here measured in feet of sea water (FSW).
But your body, from a physiological standpoint, reacts to pressure,
here measured in atmospheres absolute (AtA).
| Using these terms, you see in this table that, at the
surface, the pressure on your body is one atmosphere. This is the pressure that results
from the weight of the air in space pressing down on you. As you descend in the water,
this pressure increases e.g. at 33 FSW the pressure is 2 AtA, etc. |
| Depth and Pressure |
| Depth |
Pressure |
Feet
of
Sea Water
(FSW) |
Atmospheres
Absolute
(AtA) |
| 00 |
1 |
| 33 |
2 |
| 66 |
3 |
| 99 |
4 |
|
In the pages that follow it will be necessary to convert FSW to AtA and visa versa. The
formulas below will be used for that purpose.
Given FSW find AtA: (FSW/33) + 1 = AtA
Example: Given a dive to 130 feet of sea water (FSW), find the pressure in
atmospheres absolute (AtA).
Answer: (130/33) + 1 = 4.94 AtA
Or
Given AtA find FSW: (AtA-1) X 33 = FSW
Example: Given a pressure of 7 atmospheres absolute (AtA), find the depth in feet of
seawater (FSW).
Answer: (7 - 1) X 33 = 198 FSW
Note: When converting depth in fresh water (FFW) to pressure (AtA) and
visa versa, use the constant 34 feet/AtA instead of the 33 feet/AtA used for sea water.
This change will account for the fact that fresh water is 3% less dense than sea water.
|
