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Some mathematical formula

  1. Oct 11, 2012 #1
    Hi could you please help me out with a formula?
    So imagine this abstract cylinder and a piston moving in it , I have let's say an x amount of gas in it and all the other parameters like stroke diameter and so on , by what formula could I calculate the pressure that the gas will have when the piston will reach it's maximum upper point?
  2. jcsd
  3. Oct 13, 2012 #2
    PV=nRT is the ideal gas equation.

    I'm not sure if i'm missing something related to an "abstract cylinder"....

    Re-arranging for pressure give p = nRT/V

    p = pressure
    n = number of moles of gas
    R = 8.31
    T = temperature in Kelvin
    V = Volume of container

    I hope that helps
  4. Oct 13, 2012 #3


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    The ideal gas equation (and note the word 'ideal'; in practice, things can be a bit different) won't be enough to give you an answer. You will need to supply information regarding heat transfer. If you make the simplifying assumption that things happen too quickly for any significant heat flow than you can also use the adiabatic expansion/compression equation. (q.v.)
  5. Oct 15, 2012 #4
    note that the change in volume will be Pi*r^2*s, where r is the radius of the piston, s is the distance it moves.
    you are going to need to assume the volume and temperature have some kind of relation from thermo laws to deal with T in the equation.

    you could prolly use P=f(V) and use derivitaves to get the change.
  6. Oct 16, 2012 #5
    Thank you for giving me insight:)
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