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Why is atmospheric pressure the same indoors?

  1. Feb 8, 2013 #1
    Hi, apologies in advance as I feel stupid for asking this, but believe me I tried googling. The typical explanation for atmospheric pressure is that there is a column of air sitting on us, creating a pressure of 101 kPa. But what if there's a ceiling above us? Now only a few feet of molecules is directly above our heads. Why doesn't atmospheric pressure change? I remember vaguely from a physics course that it's related to pressure being a state function only dependent on elevation, and that pressure is applied in all directions at the given elevation. So I can understand that my arms may feel the 101 kpa pressure, but if I'm indoors, why does the top of my head still feel the same 101 kpa pressure?
  2. jcsd
  3. Feb 8, 2013 #2


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    Staff: Mentor

    Welcome to PF!
    Imagine you pumped all the air out of your house. Is your house air tight? What keeps the air from pouring off the roof of your house and in through the cracks between your front door and its frame?
  4. Feb 9, 2013 #3
    ok, so I guess a better explanation of atmospheric pressure is that there is a density gradient of air, with the density being heaviest at ground level?
  5. Feb 9, 2013 #4
    I guess my main point of confusion is when people explain atmospheric pressure to me as a column of air above our heads, extending miles into the air, which would mean the 101kPa pressure is from the billions of air molecules pressing down on my head, which makes sense only if you're outdoors
  6. Feb 9, 2013 #5


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    Staff Emeritus
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    Well, this column likes to seep through any tiny crack and push in from all sides.
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