Dynamic Viscosity

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Dynamic Viscosity

Of a fluid, 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. Also called coefficient of molecular viscosity, coefficient of viscosity. </dd>
For the dynamic viscosity of a perfect gas, the kinetic theory of gases gives

Missing Image:img src="SP7-d_files/89dyvis.gif" height="21" width="94"
where Missing Image:img src="SP7-d_files/rhosm.gif" 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 Missing Image:img src="SP7-d_files/lbar.gif" is the mean free path. For dry air at 0� C, the dynamic viscosity is about 1.7 * 10-4 gram per centimeter per second. </dd>
Whereas the dynamic viscosity of most gases increases with increasing temperature, that of most liquids, including water, decreases rapidly with increasing temperature. </dd>


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use