Viscosity is a measure of a fluids resistance to flow. It describes the internal friction of a moving fluid, and a fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion. Viscosity can also be thought of as a measure of a fluids thickness or its resistance to objects passing through it. The SI unit of viscosity is poiseiulle (PI), and its other units are newton-second per square meter (N s m-2) or pascal-second (Pa s). The viscosity of liquids decreases rapidly with an increase in temperature, and the viscosity of gases increases with an increase in temperature. Viscosity is a major factor in determining the forces that must be overcome when fluids are used in lubrication and transported in pipelines. There are two ways to measure the fluids viscosity: dynamic viscosity (absolute viscosity) and kinematic viscosity.