Wednesday, August 4, 2010

Simulation of brownian motion and diffusion

With regard to questions that came up under the friction post.
This is a nice simulation which helps visualise what happens.


  1. This looks like a random walk. If the friction is a random process how is it that the particle slows down in the direction of travel overall?

  2. It is a random walk. The diffusion constant is proportional to the coefficient of friction of the particle in the fluid.
    This reflects the profound idea, first proposed by Einstein, of a fluctuation-dissipation relation. Friction and diffusion and two sides of the same coin...