Apparent viscosity
![The apparent viscosity of a fluid depends on the shear rate at which it is measured. The apparent viscosity of a dilatant fluid is higher when measured at a higher shear rate (η₄ is higher than η₃), while the apparent viscosity of a Bingham plastic is lower (η₂ is lower than η₁).](/Images/godic/202412/21/Apparent_viscosity.svg2207.png")
Apparent viscosity (sometimes denoted η) is the shear stress applied to a fluid divided by the shear rate (![\eta = \frac{\tau}{\dot\gamma}](/Images/godic/202412/21/a6cf7500ec520b4da19c7d3484c9ed362207.png")
). For a Newtonian fluid, the apparent viscosity is constant, and equal to the Newtonian viscosity of the fluid, but for non-Newtonian fluids, the apparent viscosity depends on the shear rate. Apparent viscosity has the SI derived unit Pa·s (Pascal-second, but the centipoise is frequently used in practice: (1 mPa·s = 1 cP).