Applications of viscosity

Viscosity governs a wide range of practical, everyday choices and technologies. (1) A lubricant used for heavy machinery parts must have a HIGH coefficient of viscosity, and choosing the right lubricant requires knowing not just its viscosity but how that viscosity changes with temperature -- as temperature increases, the viscosity of a liquid DECREASES, so an oil chosen for a hot-running heavy machine must be selected with this drop in mind. Light machinery, such as car engines, instead uses oils with LOW viscosity. (2) Highly viscous liquids are deliberately used to damp the motion of delicate instruments, and are also used as the brake oil in hydraulic braking systems, where controlled, viscous resistance to flow is exactly what is wanted. (3) The circulation of blood through the arteries and veins of the human body depends directly on the viscosity of blood -- a change in blood viscosity (from dehydration, or from a medical condition) directly affects how easily the heart can pump blood through the circulatory system. (4) Robert Millikan's famous oil-drop experiment, which measured the electric charge of a single electron, relied on k …