Dynamic viscosity

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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-1s-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.

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