I am sitting inside a closed room with a cement ceiling just above my head. The pressure of the atmosphere is exerted on the ceiling from above(outside). But solid cement not being a fluid does not transport that pressure into my room. But i still feel the atm pressure which has no way to be transported into the room.I do not boil to death or anything. How does this happen?
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3 Answers
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We'll assume all the rooms and other containers are airtight, and that temperature is constant, for sake of simplicity.
If you put a mass of air in a bottle and seal it, it exerts pressure on the inside of the bottle. The pressure is dependent only on the amount of air, the volume of the bottle and the temperature. Since the bottle is rigid the volume does not change, and we're assuming constant temperature, so there's really no difference between that bottle of air in space than at sea level. The pressure inside is the same.
The same goes for a closed room. The air pressure on your body doesn't change when you close the door, because the air inside the room is the same amount at the same volume and temperature as before. At this point you could use a ridiculously large crane to lift the whole room into space and you still wouldn't boil away, because you're in a sealed room and the air pressure stays the same around you as you go from the ground into space. The air pressure outside the room changes, but luckily your concrete room is inelastic, so it "holds in" the pressure.
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$\begingroup$ I feel stupid for asking this question years ago, but I hope it's not too late to thank you for a clear answer $\endgroup$– N.S.JOHNAug 21, 2019 at 3:33
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You had to enter the room somehow. When you did, air rushed in until the pressure in the room matched the pressure of the outside atmosphere and your body parts.
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$\begingroup$ @N.S.JOHN If air didn't rush in when you opened the door, that's because there already was air in the room before you opened it. Maybe you were not the first person who ever opened the door. Or, if you were the first, maybe air got in there when the room was constructed. $\endgroup$ Dec 30, 2015 at 16:13
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That is really simple. You simply don’t get crushed because, there’s air inside you which has exactly the same pressure as the air outside your body, which has a zero net effect. Thus you live! The pressures are exerted in the opposite direction, and thus cancel out.
answered Dec 30, 2015 at 14:48
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$\begingroup$ I don't get crushed?? I should boil or burst open due to my internal blood pressure $\endgroup$– N.S.JOHNDec 30, 2015 at 14:49
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$\begingroup$ Why would you boil? I have explained that why don’t you get crushed, they reason you don’t burst is, that there is air around you too! If the air inside you wants to go out, the air outside you wants to push you inwards. So you don’t burst! I don’t know about the blood pressure, as I’m not a biology student! :p $\endgroup$ Dec 30, 2015 at 14:53
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$\begingroup$ The pressure of the air above the ceiling is already withstood by the ceiling. So only the pressure of the air inside the room is exerted on me. Which should be very small. $\endgroup$– N.S.JOHNDec 30, 2015 at 14:53
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$\begingroup$ Its the internal blood pressure that balances the outside atm pressure. $\endgroup$– N.S.JOHNDec 30, 2015 at 14:54
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1$\begingroup$ @N.S.JOHN, Pressure in a fluid such as air does not only come from the top down. It comes from every direction. Imagine that your room contains vacuum (i.e., no air). If you open a hole in the floor, air will rush in just the same as if you'd opened a hole in the ceiling, and the pressure inside will equalize with the pressure outside either way. $\endgroup$ Dec 30, 2015 at 16:17