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Adiabatic Cooling Help

  1. Apr 30, 2015 #1
    1. The problem statement, all variables and given/known data
    A pocket of air rises 1000 meters. Estimate how much it cools. Use the atmospheric law to determine pressure at 1000 meters.

    2. Relevant equations
    P = P0 * e-Mgz/RT
    PVγ = constant
    TVγ-1 = constant

    3. The attempt at a solution
    Using the atmospheric law, I found the pressure at 1000 meters to be 90202 Pa, or about 0.89 atm. I'm not sure how to use the adiabatic equations. I just assumed V1 was 1 m3, and also assumed that γ=(5/7), as the atmosphere is mainly diatomic. Plugging these in, I got that the gas expands to about 1.09 m3, but when I tried to plug that into my last equation, I got that the gas actually HEATS up, which I know is wrong. What did I do wrong??? Please help!
     
  2. jcsd
  3. Apr 30, 2015 #2

    Quantum Defect

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    What is gamma? it should be the ratio of Cp/Cv, correct? Which is larger, Cp or Cv ? Should gamma be greater or less than one?
     
  4. May 2, 2015 #3
    Thank you! I was accidentally using γ=5/7 instead of 7/5. It works now.
     
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