Fluids can be classified into Newtonian and non-Newtonian fluids based on their response to shear stress. Newtonian fluids have a linear relationship between shear stress and the shear strain rate, following Newton's law of viscosity. Their viscosity remains constant regardless of the shear rate, making their behavior predictable and easier to analyze. Common examples include water, air, oil, and gasoline.

In contrast, non-Newtonian fluids do not follow Newton's law of viscosity, and their viscosity changes with varying shear rates. These fluids can be divided into shear-thinning, shear-thickening, and Bingham plastics.

Shear-thinning fluids, also known as pseudoplastic fluids, decrease in viscosity with an increasing shear rate. Examples include latex paint and polymer solutions, which flow more easily when subjected to force, making them useful in applications requiring easy spreading under stress.

Shear-thickening fluids, on the other hand, increase in viscosity with an increasing shear rate. A common example is a cornstarch-water mixture, which becomes more resistant to flow when agitated, providing greater resistance under stress.

Bingham plastics exhibit a different behavior; they act as solids until a specific yield stress is applied, after which they flow like fluids. Examples include toothpaste and mayonnaise, which resist initial stress but begin to flow once the yield stress is surpassed. Understanding these types of fluids is crucial for designing and analyzing various fluid systems, from pipelines to industrial processes, ensuring efficiency and proper functionality.