Viscosity is a key property in fluid mechanics that describes how easily a fluid will flow. But there’s more too it than that!
The animated video above covers all of the key things you need to know about viscosity. It explains Newton’s Law of Viscosity, the equation that describes the linear relationship between the shear stress in a flowing fluid fluid and velocity gradient, the constant of proportionality between the two terms being the fluid viscosity, $\mu$.
It also explores how viscosity varies with temperature – the viscosity of liquids reduces with increasing temperature, but for gases temperature has the opposite effect. This is explained by looking at what causes viscosity on the molecular level.
Another interesting aspect of viscosity covered in the video is non-Newtonian fluids, like shear thinning or shear thickening fluids, for which the relationship between the shear stress and the strain rate is non-linear.