Flow in which the Reynolds number is very small. Fluid dynamics encompasses an intriguing array of phenomenologically rich processes, from weather prediction in the atmosphere to the swimming of the tiniest microorganism in its natural environment. A qualitative measure of the expected behaviour in a given fluid dynamics system is found from the Reynolds number, Re = density · length · velocity/viscosity. In the case where Re is very small (much less than 1, usually), the inertia effects (momentum, acceleration, and body forces) become negligible in comparison to the viscous resistance. This situation is described as creeping flow.