# How can I think of rotational diffusion inverse seconds?

1. May 28, 2014

### Steve Drake

When thinking of a spherical shaped particle moving about under Brownian motion, one describes its motion by Diffusion. The units being $$\frac{m^2}{s}$$ 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 $$\frac{1}{s}$$ I cannot think of a way to visualize that? For e.g. a rod shaped particle, what does a
$$D_r = 10\, s^{-1}$$ as opposed to say a $$D_r = 100\, s^{-1}$$ mean? How can I visualize this like I can with a sphere moving an actual distance?
Thanks

2. May 28, 2014

### D H

Staff Emeritus