Question

How do the gas laws operate in scuba diving? I mean to exclude the rule of never holding your breath...

Answer 1

Well, what is the golden rule of scuba-diving....?

Explanation:

The golden rule of scuba is NEVER to hold your breath. Why not? Because if you got a lung-full of air, and you ascend without exhaling, the difference in pressure, caused by the difference in mass of the water above you at various depths, may cause your lungs to explode. I know you excluded this scenario in your question, but it is one your instructor will emphasize, and he should do so, because a lot of recreational divers have perished this way.

And sometimes, when you are at depth, you can watch the bubbles exhaled by yourself or your buddy, and notice their expansion as they rise to the surface....Boyle's Law operates, `PV=k`, so if pressure decreases at decreasing depth, which it certainly does, the bubbles expand. When you are in the boat and waiting for the other divers to ascend,,,sometimes you notice their air bubbles at the surface...and you are impressed by the volume of the water displaced, as the bubbles come to the surface.

Sometimes when you dive, you start with a full tank, at say `3200* "psi"`, and when you first check your gauge, (in the first few minutes), the pressure has dropped by `300-400*"psi"`, and clearly this is the effect of the air in your tank being chilled to sea water temperature....`P_2=(P_1)/T_1xxT_2`...the volume in each case is constant...and so does not appear in the combined gas equation. The rate of loss of air pressure becomes more moderate as you continue to dive. And this is a manifestation of Gay-Lusaac's law.

As to the Ideal Gas law, the more you fill your tank when refilling, means the more mass of air in your container....most of us can readily pick up a full tank...and differentiate the full tank from the empty tank just by mass.

I will try to think of some more...