Viscous force

Definition

QUICK PHRASES: Fluid friction, resistance to motion through fluid

The viscous force is the force between a body and a fluid (liquid or gas) moving past it, in a direction so as to oppose the flow of the fluid past the object. In particular, the force acts on the object in the direction in which the fluid is moving relative to it (and hence, opposite to the direction in which it is moving relative to the fluid).

Viscous force is an analogue in fluids of the force of friction.

Fluid models for viscous force

Type of fluid	Brief description of model for viscous force
ideal fluid	no viscous force
Newtonian fluid	constant viscosity, i.e., magnitude of viscous force is proportional to the speed (or the rate of shear).