Entropic forces in Brownian motion

Interest in the concept of entropic forces has risen considerably since Verlinde proposed in 2011 to interpret the force in Newton's second law and gravity as entropic forces. Brownian motion-the motion of a small particle (pollen) driven by random impulses from the surrounding molecules-may be the first example of a stochastic process in which such forces are expected to emerge. In this article, it is shown that at least two types of entropic force can be identified in three-dimensional Brownian motion. This analysis yields simple derivations of known results of Brownian motion, Hooke's law, and-applying an external (non-radial) force-Curie's law and the Langevin-Debye equation. (C) 2014 American Association of Physics Teachers.