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Thermal Velocity

  1. Mar 26, 2012 #1
    Hello, I'm new here!

    I've been trying to work out Thermal Velocity for a while and its got me stumped. First attempt was for a space example of low flying craft where the thermal velocity I was aware should be very high, somewhere around 1000m/s in some cases, but couldn't get that result. Same with a more recent attempt to follow wikipedia for a room temperature example.

    http://en.wikipedia.org/wiki/Maxwell–Boltzmann_distribution#Typical_speeds

    The gas constant related R and boltzmann k related equations pop up in all the materials I've used, but I can't get a good result from them and I'm not sure where I'm going wrong. Can anyone walk me through the example given there, and get to the correct Thermal velocity?

    It would be a great help to me, thanks.


    AH! Nevermind, I actually fixed the damn thing. Took some serious fiddling though!

    Vp = (2*k*T/m)^0.5

    m needed the molecule mass, so in the case of nitrogen

    0.028 kg/mol / Avagadros constant = 4.65E-26

    gives a thermal speed of 421 or 422 depending on the method used (R or k) probably due to rounding errors in the constants.

    I asked because I've tried to get this working before for a low earth orbit drag equation and it kept falling over, quite pleased to finally have something that actually works. Its always the simple parts you stumble on!
     
    Last edited: Mar 26, 2012
  2. jcsd
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