Which term describes the resistance of a liquid to flow?

• A. Viscosity
• B. Density
• C. Surface tension
• D. Vapor pressure

Answer: (A)

Viscosity is the measure of a liquid’s internal friction—how strongly its molecules resist moving past one another. This resistance determines how easily the liquid flows when a force is applied. A liquid with low viscosity, like water, slips past more readily and flows quickly; a high-viscosity liquid, like honey or syrup, resists motion and flows much more slowly. Temperature also plays a big role: heating lowers viscosity by giving molecules more energy to move past each other, while cooling raises it.

Density is about how much mass a given volume has, which affects buoyancy more than flow resistance. Surface tension involves the cohesive forces at a liquid’s surface, influencing droplet shape and capillary action rather than how freely the liquid flows. Vapor pressure relates to a liquid’s tendency to evaporate and is about phase change, not flow behavior.