What measurement is used to define fluid viscosity?

Viscosity is defined as a fluid's resistance to flow. It indicates how thick or thin a fluid is and how easily it can move. A fluid with high viscosity, like honey, flows slowly due to the internal friction between its molecules, whereas a fluid with low viscosity, like water, flows easily. This characteristic is essential when working with lubricants and other fluids, as it impacts their performance in various applications, such as in engines or machinery.

Other measurements, while relevant in different contexts, do not define viscosity. Longevity pertains to the lifespan of a fluid, temperature stability relates to how a fluid's properties change with temperature, and pressure sensitivity refers to how a fluid's characteristics are affected by pressure. These factors may influence how a fluid behaves but are not the defining measurement of viscosity itself.