1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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.

    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


    User Avatar
    Staff Emeritus
    Science Advisor

    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?!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Print ViewEquipartition Theorem and Microscopic Motion