What is the measurement of a fluid's resistance to flow?

Viscosity is defined as the measurement of a fluid's resistance to flow. It indicates how thick or thin a fluid is and how easily it can move or be poured. For example, honey has a higher viscosity compared to water, meaning it flows more slowly and resists motion more than water does. This property is crucial in various engineering applications, including lubrication, fluid transport, and chemical processes, where understanding the behavior of fluids in motion is essential for design and analysis.

In contrast, density refers to the mass per unit volume of a substance and is not directly related to how the fluid flows. Pressure measures the force applied by the fluid per unit area and is important in understanding how fluids behave under various conditions, but it does not specifically relate to resistance to flow. Flow rate, on the other hand, describes the volume of fluid that passes a given point in a certain period, but again, it does not provide information on the internal resistance of the fluid. Thus, viscosity is the most appropriate choice for describing a fluid's resistance to flow.