What is viscosity?

What is viscosity?

• A. A fluid's resistance to flow
• B. The density of a fluid
• C. The vapor pressure of a liquid
• D. The color of a liquid

Answer: (A)

Viscosity is a fluid's resistance to flow, arising from internal friction between adjacent layers as they move past one another. This means a high-viscosity liquid, like honey, resists pouring and flows slowly, while a low-viscosity liquid, like water, flows readily. In engineering and damage control, viscosity helps determine how easily fluids are pumped, how much pressure loss occurs in pipes, and how a lubricant film behaves between surfaces. Temperature often changes viscosity: liquids generally become less viscous as they warm up, so flow improves with temperature. The term you’ll see most in calculations is dynamic viscosity, with units of Pascal-seconds; sometimes you’ll encounter kinematic viscosity, which is dynamic viscosity divided by density. Other properties—density (mass per volume) affects inertia and buoyancy, vapor pressure relates to how readily a liquid evaporates, and color is just an optical property—do not describe how easily a fluid flows.

Viscosity is a fluid's resistance to flow, arising from internal friction between adjacent layers as they move past one another. This means a high-viscosity liquid, like honey, resists pouring and flows slowly, while a low-viscosity liquid, like water, flows readily. In engineering and damage control, viscosity helps determine how easily fluids are pumped, how much pressure loss occurs in pipes, and how a lubricant film behaves between surfaces. Temperature often changes viscosity: liquids generally become less viscous as they warm up, so flow improves with temperature. The term you’ll see most in calculations is dynamic viscosity, with units of Pascal-seconds; sometimes you’ll encounter kinematic viscosity, which is dynamic viscosity divided by density. Other properties—density (mass per volume) affects inertia and buoyancy, vapor pressure relates to how readily a liquid evaporates, and color is just an optical property—do not describe how easily a fluid flows.