# Dynamic viscosity

From AMS Glossary

## dynamic viscosity

(

*Also called*coefficient of molecular viscosity, coefficient of viscosity.) A fluid property defined as the ratio of the shearing stress to the shear of the motion.It is independent of the velocity distribution, the dimensions of the system, etc., and for a gas it is independent of pressure except at very low pressures. For the dynamic viscosity μ of a perfect gas, the kinetic theory of gases gives where ρ is the gas density,

*c*is the average speed of the random heat motion of the gas molecules and is proportional to the square root of the temperature, and*L*is the mean free path. For dry air at 0°C, the dynamic viscosity is about 1.7 × 10^{-4}g cm^{-1}s^{-1}. While the dynamic viscosity of most gases increases with increasing temperature, that of most liquids, including water, decreases rapidly with increasing temperature.*See*kinematic viscosity, eddy viscosity, Newtonian friction law.