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Homework Help: Possible to compress a vacuum?

  1. Dec 23, 2005 #1
    If a cylinder has a closed, sealed end, and the other end is a piston, and a 95% vacuum is drawn in the cylinder between the sealed end and the piston head, can the piston be depressed to "compress" the vacuum? Can the remaining 5% of air in the cylinder be compressed in any compression amount?
  2. jcsd
  3. Dec 23, 2005 #2


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    Are you serious?

    If you sucked 95% of the air out of the cylinder, what do you suppose the piston will want to do if you leave it to its own devices?
  4. Dec 23, 2005 #3
    I should have clarifed....that the piston is locked and cannot move when the vacuum is drawn on the cylinder chamber. Then, the valve to the vacuum pump is closed, leaving the 95% vacuum in the cylinder. Now, if the piston is unlocked, can the piston be depressed any amount to compress the 5% of the air remaining in the cylinder?
  5. Dec 23, 2005 #4


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    When the piston is released, it will be sucked down into the cylinder, eventually reaching a point where the pressure inside and pressure outside are equal and the piston comes to rest. It would be very possible to compress the remaining gas inside the cylinder further, after the piston is sucked down and the pressure euqalized, it would be no different than the original position the piston was in was it was a 0% vacuum.
  6. Dec 24, 2005 #5


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    As MrJ points out, you are very quickly going to have a chamber that is at 1 atm (though only 1/20th the volume it was). With your chamber of 1 atm of air, you can do whatever you want - including compress it.

    Oh, and no, you *cannot* compress vacuum - it is as non-sensical as "adding some cold" to a system.

    I think you are over-thinking this problem.
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