Viscosity
Viscosity, the resistance fluids have to flowing. The viscosity of some fluids, including gases, water, and kerosene, is relatively low; that of others, such as molasses and glycerin, is relatively high. A slow-flowing fluid—that is, one with a high viscosity—is often said to be viscous. The viscosity of liquids generally decreases with increasing temperature. Molasses, for example, is more easily poured when heated than when cold. With gases, however, the viscosity generally increases with increasing temperatures.
The viscosity of the air causes sounds to die away and the wind to drop. The viscosity of water causes waves to subside. Viscosity has an important influence on the speed of airplanes, automobiles, and boats, on the efficiency of lubricating oils, and on the flow of materials through a pipeline.