Definition of Viscous Fluid
Definition 1
A property of a fluid that produces friction within it is called viscosity.
Explanation
From a learner’s point of view the above definition of viscosity is neat and fine, but more intuitively one can describe viscosity as a kind of “stickiness.”
We commonly call fluids like air or water non-viscous (inviscid) fluids, and fluids like honey or lava viscous fluids.
The internal friction in a fluid occurs as a resistance produced when two adjacent layers of the fluid move relative to each other, and is also called the viscous force. Just as friction between solid bodies becomes thermal energy, viscosity contributes to converting a fluid’s kinetic energy into internal energy.
Raymond A. Serway. Physics for Scientists and Engineers with Modern Physics (9th): p427. ↩︎