Physics Question?

Question

There is a maximum depth at which a diver can breathe through a snorkel tube because as the depth increases, so does the pressure difference, tending to collapse the diver's lungs. Since the snorkel connects the air in the lungs to the atmosphere at the surface, the pressure inside the lungs is atmospheric pressure.

What is the external-internal pressure difference (in Pa) when the diver's lungs are at a depth of 6.1 m (about 20 ft)? Assume that the diver is in fresh water. (A scuba diver breathing from compressed air tanks can operate at greater depths than can a snorkeler, since the pressure of the air inside the scuba diver's lungs increases to match the external pressure of the water.)

Answer 1

At 20 ft., there are 20 cu. ft. of water above each sq. ft. of surface area. A cu. ft. of water weight 62.4 lbs., so that's 1248 lbs. per sq. ft.

Divide by 144 sq. in. per sq. ft. to get the pressure per sq. in. (a bit less than 10 psi). This is in addition to the 14.7 psi of air pressure at the surface of the water.

And, as you say, the air pressure is still essentially 14.7 psi inside the diver's lungs, so the pressure difference is the "somewhat less than 10 psi" you calculated in the preceding paragraph. And you can convert it to Pa.

Answer 2

one atmosphere is 33 feet or 10m isn't it? Can't you extrapolate from there? 16lbs. psi per atmosphere...just a thought.