I know this may seem like a very generic topic but I find that more often than not, freedivers are given the knowledge in order to dive, but fail to make the link between theory and application. There are also very experienced divers out there that even after years of diving still do not understand the physics of diving. This is one of the many reasons we advocate taking our Freediver or Intermediate Freediver courses here at the Oregon Freediving Company. Since man has been able to write, people have been interested in observing what is going on and documenting it. It is the ancient Greeks who were responsible for the shift to a rational belief. If you are close enough you are able to see through the magic to see the logic. Any technology is significantly advanced is discernable from magic. I know this may sound like a romantic Novel but the majority of our community sees the magic of freediving, and what I would like you to now see, is the logic behind it all.
Today I would like to shed light on how I see pressure and why pressure affects the body. So…. What is pressure? Continuous physical force exerted on or against an object by something in contact with it. Or force per unit area!
Now, for the most part, I strongly advocate using the metric system for freediving but in terms of understanding pressure I found the imperial system to really help.
At sea-level, we are exposed to about 14.7 pounds per square inch (psi) of pressure. This means that each square inch of our bodies has the equivalent force of about 14.7 pounds pressing on it. This pressure is actually a result of the weight of the air in Earth’s atmosphere.
As it turns out, if you took a column of air, one square inch in cross-section, that would extend from sea-level all the way to the edge of the atmosphere, all the gas molecules in that column of air would have a combined weight of about 14.7 pounds — which leads to 14.7 psi of pressure at sea level.
With that information in mind, and “atmosphere” is defined as a unit measurement of pressure that is equal to the pressure caused by the earth’s atmosphere at sea level….. Which just happens to be 14.7psi. Like air, water causes pressure by its weight. But of course, water is considerably denser than air. A column of sea water one inch in cross-section would need to be only about 10 meters tall to weigh 14.7 pounds. Therefore, at a depth of 10 meters beneath the sea surface, the total ambient pressure is about 29.4 psi, or 2 ATM which is 1 ATM caused by the weight of the air in Earth’s atmosphere, plus 1 ATM for the weight of 10 meters of seawater.
Even as a scuba diving instructor, this piece of the puzzle really didn’t click. I always understood what pressure was and how it affected me, but never why. These are the things that excite me as a diver, and if you feel the same, then join us on course. You won’t regret it.