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Atmospheric Pressure Sounds Intense

  1. Jan 29, 2012 #1
    Ok, so 1 atm≈101,300 Pa that is 101,300 newtons per square meter, presumably at sea level. If we look at the force in terms of lbs this is 101,300 N* (.225 lb/1 N)≈22,792 lb.

    The pressure per square meter seems pretty intense to me when I thought of it in terms of force. I didn't ask my instructor about this because I didn't notice at first. It's bizarre; how can their be that much force without things being crushed?

    At first I thought that it might have something to do with pressure being equal in all directions, so that the forces maybe cancel at some particular depth i.e. a net force is 0. However, that would imply that a planet's atmosphere could not be crushing; we might as well be on Venus.
  2. jcsd
  3. Jan 29, 2012 #2
    Yes, and that's because a 7 mile high column of air weighs down on the Earth's surface.
  4. Jan 30, 2012 #3
    Yeah, I understand why there's so much pressure, what I don't fully understand is why this pressure isn't more crushing than you would intuitively anticipate. Every square meter there's over 20 thousand lbs of force according to that little calculation I did.

    I think the forces just largely cancel softening the net force, since pressure is the same in all directions.
    Last edited: Jan 30, 2012
  5. Jan 30, 2012 #4
    It is very crushing, but it gets compensated, not from all sides, but from the inside and outside. When you try to inhale, your diaphragm reduces the internal pressure a little bit, so that the lungs fill up with air, and, conversely, it increases it a little more when you try to exhale.

    The pressure of a column of air that is 10.3 m high has the same hydrostatic pressure as the atmospheric pressure. Yet, the maximum depth you could go with a snorkel is around 50 cm, i.e. one twentieth of that. Anything deeper would place too much of a load on your lungs that you won't be able to inhale or exhale.

    So, your calculation was right in some sense. Suppose your lungs are 30 cm x 20 cm. That is an area of 0.06 m2. Atmospheric pressure causes a pressure force of 6 kN, the equivalent of the weight of 600 kg (1,320 lb) on your chest and back! One twentieth of that is 30 kg (66 lb). So, this brings the calculated numbers to the ballpark of intuition. You see, it is this uncompensated extra pressure from the water that our bodies were not designed to tollerate. Even moderate depths cause failure.
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