Why is there atmospheric pressure? Gas molecules have empty spaces between them right (intermolecular space). But to have atmospheric pressure all the gas pressure will have to line up without any space. Imagine lifting 3 boxes. Box 1 is stack ontop of box 2 and ontop of box 3. Between box 1 and 2, there is an empty space, and the same thing with box 2 and 3. If this is the case then I am only experiencing the weight(force) of 1 box not 3 boxes(because box 2 and 3 have spaces between them). This is how I imagine atmospheric pressure. I know this is wrong, but why is it wrong?
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$\begingroup$ There is space between the atoms of a solid too. Just not as much $\endgroup$– R. EmeryCommented Jan 10, 2021 at 1:43
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4 Answers
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You're missing the fact that those molecules are moving really fast and they're collidingwith each other. Take into accoutn that the can be over $10^{25}$ molecules...
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Take a look at the great animations made by Colorado University: https://phet.colorado.edu/sims/html/gases-intro/latest/gases-intro_en.html
Gas molecules have gaps between them, but that doesn't stop the group of molecules on a certain level to support another group of molecules above it. They do so by collision.
In the simulation, try to insert some heavy molecules and see that if the molecules are denser below they as a whole can support the molecules above.
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Unlike your static boxes, in this case pressure is defined from the time-averaging of forces exerted by molecules impinging on a surface.
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Here floating boxes don't give any force to the rest. But air molecules do. And its the main cause of atmospheric pressure.
