A measure of a fluid's resistance to flow. Do not confuse the term viscous with vicious (mean and nasty!). Additional Info: Liquids such as molasses or motor oil are examples of highly viscous substances. The viscosity of a liquid generally decreases as the temperature is increased. For example, warm molasses is easier to pour and stir than cold molasses because it has a lower viscosity when warm. Two common units of viscosity are the poise which is 1 dyne per second per square centimeter and thecentipoise (100 centipoise = 1 poise). These can also be expressed as (Newton)(second) per square meter. Gases also have a resistance to flow, although these viscosities are much lower than for liquids. When selecting a stirring motor for use with viscous liquids, one generally needs to purchase a unit that has a geared motor that provides the necessary torque. Safety Emporium has a handy selection chart on its lab stirrers page. MSDS Relevance: MSDS's are required to list known physical properties such as viscosity (if known and/or relevant). Viscous materials pour slowly and may be difficult to stir. In general, the viscosity of a syrupy material tends to decrease as the temperature increases. See also: Area Units