A Newtonian fluid is a type of fluid that exhibits constant viscosity behavior, meaning that its viscosity remains constant regardless of the shear rate or applied shear force. These fluids follow Newton's flow law, which states that the shear rate is proportional to the shear force. An example of a Newtonian fluid is water, where the viscosity remains constant at different shear rates. Other examples include gas oil and some lubricating oils. Newtonian fluids are of practical importance in many areas of industry, from chemistry to food processing, because they exhibit a predictable response to forces and deformations.