FAQ About Fluid Mechanics

A frictional force occurs between two fluid layers moving at different speeds. The slow moving flow layer tries to slow down the faster moving flow layer. This internal resistance to flow is called viscosity. Viscosity occurs in liquids due to the intermolecular force of attraction, while in gases it occurs due to the collisions of molecules.

Flows in which friction effects are significant are called viscous flows. In flow regions, the greatest viscosity occurs at or near the surface of the solid. Far from the surface, the viscosity is negligibly small. Flows where the viscosity is so low that it is negligible are called inviscous flows.