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How can I think of rotational diffusion inverse seconds?

  1. May 28, 2014 #1
    When thinking of a spherical shaped particle moving about under Brownian motion, one describes its motion by Diffusion. The units being [tex]\frac{m^2}{s}[/tex] I can understand this physically as a distance it will travel from a certain point in space averaged over x-y and z direction.
    Now rotational diffusion on the other hand has units of inverse seconds [tex]\frac{1}{s}[/tex] I cannot think of a way to visualize that? For e.g. a rod shaped particle, what does a
    [tex]D_r = 10\, s^{-1}[/tex] as opposed to say a [tex]D_r = 100\, s^{-1}[/tex] mean? How can I visualize this like I can with a sphere moving an actual distance?
  2. jcsd
  3. May 28, 2014 #2

    D H

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    Think of rotational diffusion as having units radian2/s instead of 1/s.
  4. May 28, 2014 #3
    Hi, Thanks

    That makes a big more sense...

    So in a geometrical sense... if a rod's center of mass with fixed in a liquid somehow, but it could still rotate around that point, does this mean the distance its ends would 'trace' out on a hypothetical sphere in 1 second would equal eg 40 radians?... I am still a bit confused thanks
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