Viscosity is best described as which property?

• A. A measure of a fluid's resistance to flow
• B. Its color
• C. Its density
• D. Its pH level

Answer: (A)

Viscosity describes how much a fluid resists flowing when a force is applied. It’s about internal friction between the fluid’s molecules as layers slide past one another, so thicker liquids (like honey) flow slowly, while thinner liquids (like water) flow readily. This property is different from color, density, or pH—color is about light absorption, density is mass per volume, and pH is a measure of acidity. Temperature and composition influence viscosity: heating typically lowers it, making liquids flow more easily, while thickening agents raise it. In practice, viscosity is measured with units like Pascal-seconds for liquids, and some fluids change viscosity with the rate at which they’re stirred or sheared (non-Newtonian behavior).