It resists the relative motion of objects immersed a fluid and the relative motion of layers with differing speeds within a fluid. Despite its title, the International System of Units has had very little impact on viscosity. The pascal second is rarely used in scientific and technical publication. Pastes, gels, emulsions, and other complex compounds are harder to summarize. Some fats like butter or margarine are so viscous that they seem more like soft solids than like flowing liquids.
Molten glass is extremely viscous and approaches infinite viscosity as it solidifies.
It is frequently measured using a device called a capillary viscometer. When two fluids of equal volume are placed in identical capillary viscometers and allowed to flow by gravity, a viscous fluid takes longer than a less viscous fluid to flow through the capillary. However, this unit is so large that it is rarely used. Motor Oil Motor oil is like every other fluid in that its viscosity varies with temperature and pressure. Since the conditions under which most automobiles will be operated can be anticipated, the behavior of motor oil can be specified in advance.