Viscosity:

Viscosity characterizes the motion of fluids in the presence of a mechanical shear force. All fluids can flow, and the resistance they pose to such flow is called VISCOSITY.  A fluid passing through a capillary experiences a retarding force from the walls of the tube, resulting in a higher velocity along the central axis than at the walls. For any given small bore capillary, it is found that a specified volume of fluid, of density, ρ, flows through the capillary in a time, t, given by the