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Old Jun 6th 2016, 01:53 PM   #1
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Join Date: Jun 2010
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Gage Reading is NOT a pressure.

Some beginning students think the reading of a gage (G.R.) is a pressure. The reading is not a pressure -
the reading is a pressure difference.

The idea "zero pressure," as a gas pressure numerically "zero" is incorrect. Pressures of a gas happens
with momentum exchange of the continuum of gas particles. As there are fewer and fewer particles (headed
toward zero pressure) a limit is reached. The continuum breaks down, the idea "pressure" is no
longer valid and the gas comes to obey "free-molecular flow" behaviors.

Absolute pressure! Texts say, "G.R. plus atmospheric pressure equals absolute pressure." Not so!
"G.R. plus atmospheric pressure equals pressure." "Absolute is a superfluous, confusing adjective.

Also, All pressures are relative.
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