What is the term used to define the measure of a fluid's internal resistance to flow?

The measure of a fluid's internal resistance to flow is defined as viscosity. Viscosity quantifies how easily a fluid can deform and flow under an applied stress. This characteristic is crucial in various engineering and lubrication applications, as it affects how fluids behave in motion and their ability to provide effective lubrication to machinery components.

Fluids with high viscosity are thicker and flow more slowly, while those with low viscosity are thinner and flow more quickly. Understanding viscosity is essential for technicians as they select the appropriate lubricants for specific applications to ensure optimal performance and protection of machinery.

In contrast to viscosity, density refers to the mass per unit volume of a substance, specific gravity compares the density of a substance to that of a reference substance (usually water), and fluidity is a more general term that describes how freely a fluid can flow, but does not provide the specific measurement that viscosity does. Therefore, the correct term that specifically measures a fluid's resistance to flow is viscosity.