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Print ViewEquipartition Theorem and Microscopic Motion

  1. Nov 13, 2007 #1
    What is the typical rotational frequency f_rot for a molecule like N_2 (nitrogen) at room temperature (25 C)? Assume that d for this molecule is 1 angstrom = 10^{-10} m. Take the atomic mass of N_2 to be 4.65 * 10^{-26} kg.
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    I know that the rms angular speed which is the root mean square (rms) of the x component of velocity of the gas particles is = sqrt(2k_B(T)/(m(d^2))) where k_B is the Boltzman constant 1.38*10^-23 J/K.
     
    Last edited: Nov 14, 2007
  2. jcsd
  3. Nov 14, 2007 #2

    Astronuc

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    Staff: Mentor

    Think about moment of inertia. How much of the energy is distributed in rotational motion versus translational motion?

    Or assuming the rotational motion comes from collisions based on a translational speed, how does one transform the typical translational speed into a rotational velocity?
     
  4. Nov 14, 2007 #3
    what do i do with the rotational speed that i calculated to get rotational frequency??'

    molecule has moment of inertia I about the axis and is rotating with angular velocity omega about that axis with associated rotational kinetic energy (1/2) I omega_x^2
     
    Last edited: Nov 14, 2007
  5. Nov 14, 2007 #4
    all righty. i found this equation relating frequency and veolcity --> angular velocity=2(pi)f
    but i DONT UNDERSTAND why i'm not getting the right answer. i get velocity to be 4.2057*10^12 m/s and i SHOULD be able to get frequency by dividing it by 2pi, but f=6.69*10^11 is not right!

    whats wrOong?!
     
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