MadSci Network: Earth Sciences
Query:

Re: When submarines dive, is pressure greater on the inside or the outside?

Date: Wed Feb 16 08:01:22 2000
Posted By: Carlin Gregory, , Chemistry (BA and MS) in Synthetic , Williams Gas Pipelines - Texas Gas
Area of science: Earth Sciences
ID: 950299459.Es
Message:

Paul, regarding your question on the pressure inside and outside any 
airplane.  The answer is that the pressure is relative to standard 
pressure, that is what the pressure is at ground level, 14 pounds per 
square inch.  Since air pressure gets smaller the higher you go up, and an 
absolute vacuum would be 0 pounds per square inch (psi), the highest
pressure difference between the outside and inside of a plane is 14 psi.  
This pressure is easily overcone by the structural integrity of the 
plane.  And this is also the reason why the pilots cannot be crushed by 
the pressure inside the plane.  The cabin pressure is attempting to 
maintain ground pressure or about 14 psi. Since pressure on the ground is 
14 psi, and that pressure is what is maintained by the cabin, the pilots 
would feel just the same as they would on the ground, no matter how high 
they flew.  However, if you take a plane down to the ocean bottom where 
outside pressures are much greater, (pressure increases by 14 pounds every 
33 feet) the cabin would crush and the pilots as well because the pressure 
difference is much much greater.  Pressure 1 mile down would be well over 
one ton per square inch!!!!!  Submarines are built to withstand these 
pressure, but even they have depth limits.  Hope this helps.  -- Carlin 
Gregory, Williams Gas Pipelines-Texas Gas



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