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# Air Pressure Again

A metal box, opened on the top, in put on the ground, then it’s closed welding a metal surface on it, in order to obtain a parallelepiped full of air. Suppose that the box walls are so strong that they would be perfectly resistant to the outside air pressure even if the box was empty. Then the air inside the box isn’t subjected to any influence by the external air pressure. In other words, standing inside the box there is no way to understand if outside there is air or empty space. Now, according to Stevin’s law, the pressure on the bottom surface inside the box should be equal to dgh, where h is the box height, much less than the air pressure outside! But actually the internal pressure is the same as the external pressure. I can’t find the mistake. Moreover i can’t understand how the pressure p in the gas law pV=nRT is involved in all that. thank you.

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