Boyle's law incorrectly used throughout the freediving literature | DeeperBlue.com Forums
  Guest viewing is limited
  • Welcome to the DeeperBlue.com Forums, the largest online community dedicated to Freediving, Scuba Diving and Spearfishing. To gain full access to the DeeperBlue.com Forums you must register for a free account. As a registered member you will be able to:

    • Join over 44,280+ fellow diving enthusiasts from around the world on this forum
    • Participate in and browse from over 516,210+ posts.
    • Communicate privately with other divers from around the world.
    • Post your own photos or view from 7,441+ user submitted images.
    • All this and much more...

    You can gain access to all this absolutely free when you register for an account, so sign up today!

Boyle's law incorrectly used throughout the freediving literature

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.

VincentMicah

New Member
Apr 14, 2020
6
2
3
30
Boyle's law states that at constant temperature, the volume of a given amount of gas is inversely proportional to its pressure. If you've taken a freediving class you've probably been taught that if you dive to 90m you will experience a 10-fold increase in pressure, and therefore the air in your lungs will get compressed to a 10th of the volume it occupied at the surface.

Well, no, not quite, because if we're talking about the air inside your lungs, then to apply Boyle's law we have to use the pressure inside your lungs too, and having 10 atmospheres of environment pressure does not mean there's 10 atmospheres also in your lungs. It's certainly not the case for a submarine: if a U-boat goes down to 90m, the pressure inside the vessel does not increase 10-fold, so why would it be for your lungs? True, your thoracic cage is more flexible than a sub, but your ribs will still oppose those 10 atmospheres quite stubbornly.
 
  • Like
Reactions: xristos

Nathan Vinski

Well-Known Member
Apr 19, 2015
279
179
83
25
Realistically speaking, there will be a tiny difference as the ribs, and tissues will exert some outward force. However, the body isn't that strong compared to water, so the vast majority (it's probably not been tested, but I'd assume somewhere near 99%) of outward force is created by the air-pressure in the lungs.

According to boyle's law, air needs to be compressed to 1/x the absolute external pressure to exert outward force that's equal to the inward force.

of you consider that the ribs may provide some tiny amount resistance, realistically we're probably looking at a ratio of something like 0.99/x

--

Of course, you can mechanically exert more outward force with the muscles, but in freediving we call this 'Tension'.

Tension in the breathing muscles is the #1 factor in causing shallow (less than ~50m) Lung-squeeze (pulmonary oedema) or the inability to equalize. (if internal pressure is less than external pressure, you can't equalize: Equalize means = pressure on both sides.)

--

Now what about at great depths (deeper than 50m), below the point where the ribs can no longer be mechanically compressed.

again, the body isn't that strong. If nothing happened and the internal pressure stopped increasing, they would probably crack or dislocate due to the enormous external inward force.

At this point the blood vessels on the alveoli become swollen, and this swelling displaces the air further, to the point where the internal pressure is nearly equal to the external pressure: Probably something like 99% or 0.99/x volume.

Again, if it wasn't near-equal, the body would be destroyed & equalization of the ears would be impossible..
 

VincentMicah

New Member
Apr 14, 2020
6
2
3
30
Boyle's law states that at constant temperature, the volume of a given amount of gas is inversely proportional to its pressure. If you've taken a freediving class you've probably been taught that if you dive to 90m you will experience a 10-fold increase in pressure, and therefore the air in your lungs will get compressed to a 10th of the volume it occupied at the surface.

Well, no, not quite, because if we're talking about the air inside your lun
appvalley tutuapp tweakboxgs, then to apply Boyle's law we have to use the pressure inside your lungs too, and having 10 atmospheres of environment pressure does not mean there's 10 atmospheres also in your lungs. It's certainly not the case for a submarine: if a U-boat goes down to 90m, the pressure inside the vessel does not increase 10-fold, so why would it be for your lungs? True, your thoracic cage is more flexible than a sub, but your ribs will still oppose those 10 atmospheres quite stubbornly.

issue solved!!
 
DeeperBlue.com - The Worlds Largest Community Dedicated To Freediving, Scuba Diving and Spearfishing

ABOUT US

ISSN 1469-865X | Copyright © 1996 - 2021 deeperblue.net limited.

DeeperBlue.com is the World's Largest Community dedicated to Freediving, Scuba Diving, Spearfishing and Diving Travel.

We've been dedicated to bringing you the freshest news, features and discussions from around the underwater world since 1996.

ADVERT