What are scientists measuring when they assess a liquid's resistance to flow?

When scientists assess a liquid's resistance to flow, they are measuring viscosity. Viscosity refers to the internal friction of a fluid, which determines how easily it flows. A liquid with high viscosity, like honey, flows slowly due to its thicker consistency, while a liquid with low viscosity, like water, flows much more freely.

In the context of this question, density, volume, and temperature do not directly relate to the measurement of resistance to flow. Density refers to the mass per unit volume of a substance, volume is the amount of space that a substance occupies, and temperature measures the kinetic energy of molecules within a substance. While each of these properties is important in its own right, they do not specifically pertain to how a liquid flows, which is the essence of viscosity. Therefore, measuring viscosity gives a clear understanding of a liquid's flow behavior.