In the book of Risken, Fokker-Planck equations, at page 36, it has been stated that
If we think of the Langevin force as a successive number of peaked functions with nearly zero width and nearly infinite height, the velocity then consists of a successive number of peaked functions with width $\sim \gamma $ and height $\sim \gamma^{-1}$. Neglecting the time derivative in (3.1) is therefore equivalent to replacing the peaked functions with width $\gamma$ by peaked functions with nearly zero width in the velocity. If we are interested only in the slow motion of (3.14) this replacement therefore leads to the same result.
I'm not sure how the author is coming up with this interpretation of overdamped Langevin equation. Does anybody have an explanation?
