What is viscosity a measure of?

Viscosity is the measure of a fluid's resistance to flow, which is fundamentally linked to how its molecules interact with one another. When we refer to viscosity, we are discussing how easily the molecules in a liquid can move past one another; a fluid with high viscosity behaves more like a solid because its molecules are more tightly packed and resist motion, while a fluid with low viscosity flows more freely.

In practical terms, you might think of syrup versus water. Syrup has a high viscosity due to greater molecular cohesion, making it flow slowly compared to water, which has a low viscosity and flows easily. This characteristic is crucial in many building maintenance tasks, especially in understanding how different fluids will behave in systems such as plumbing or in the application of paints and coatings.

The other options relate to different properties of fluids but do not accurately define viscosity. Weight pertains to the force exerted by gravity on an object, temperature describes how hot or cold a substance is, and volume measures how much space a fluid occupies. None of these capture the essence of how fluid molecules interact in terms of resistance to flow.