Gauge Pressure of Space ```Name: Rod M. Status: Other Age: 60s Location: N/A Country: N/A Date: 2001 ``` Question: If space is a vacuum, how much of a vacuum reading would I get, if I were to simulate the atmospheric pressure of earth within a space ship, and run a line from the inside of the space craft through the wall of the craft and take a reading with a standard vacuum gauge which works by measuring inches of mercury (the type used in the automotive industry for measuring engine vacuum)? Replies: You would read a pressure of about 1atm = 760 mm Hg of air pressure within the space craft. The pressure outside the space craft would still be essentially zero because the escaping air would quickly expand into an ever increasing volume. Vince Calder Hi, Rod !! If I have understood your question, you wish to know how would be the reading of a vacuum gauge, if you measure the space vacuum, right? It would be 760 mm/Hg. As you know, VACUUM is the pressure UNDER the atmospheric pressure. In the universe, between planets, you can find almost the absolute zero pressure. It is however not really ZERO, because there is a small quantity of hydrogen and/or molecules in the space. But, anyway, you will measure 760 mm of Mercury as vacuum. Best regards Alcir Grohmann Atmospheric pressure is 760 millimeters of mercury. So the difference between the vacuum of space and the inside of a spacecraft maintained at atmospheric pressure will be the same 760 mm Hg. Richard E. Barrans Jr., Ph.D. Assistant Director PG Research Foundation, Darien, Illinois You would get a reading of a perfect vacuum; space is closer to a perfect vacuum than anything we can produce on earth. A perfect vacuum is described by your pressure gauge as 76 cm or 30 inches of mercury. This corresponds to 15 psi and, of course, measures how much greater the air pressure is inside the spaceship than outside. This means that spaceships must have strong walls to keep from blowing up due to the internal pressure. Even a six foot diameter sphere has a pressure of about 122 tons trying to blow it apart due to the atmospheric pressure of 15 psi (pounds per square inch) inside the spaceship (if you simulate the atmospheric pressure of the earth.) Best, Dick Plano Click here to return to the Engineering Archives

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