I saw a video the other day explaining air pressure where a teacher breaks a ruler by hitting it over a table underneath a sheet of newspaper. I get generally how that works. But then she said atmospheric pressure is 14 psi and so the whole sheet has 7000lb of pressure on it. That’s BS right? Like it clearly doesn’t have 7000 lbs pressed against it? Isn’t that the weight of the column of air above it?
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There are 2 forms of PSI rating that people will refer too. The one most people commonly refer to is PSIg. This is the difference between the atmosphere and whatever your containing. There is also PSIa which is the absolute pressure for any system. 0 PSIg = 1PSIa (Atmospheric pressure)
Yes that paper has 7000lbs of air on top of it even though for everyday things, that number is irrelevant because there is no pressure difference between the two. That number only comes into the play when there is a pressure differential generated across the paper sheet for that force to take effect. If you were to create the most perfect vacuum possible and use an unbreakable sheet of paper as the seal for that vacuum, it would experience 7000lbs of force across it. However air is tiny and likes to move so that vacuum is broken almost instantly that moment any counteracting force is applied against the paper. Same concept as water and drag. The faster you move, the less time water has to move out the way, and the more its force begins to apply.
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