Newtonian fluids

Newtonian fluids are liquids whose viscosity—the measure of their thickness or resistance to flow—remains constant regardless of the amount of force or shear applied to them. This means they flow consistently under different conditions. Common examples include water, air, and mineral oils. For instance, when you stir water faster or slower, its resistance to your stirring doesn't change; it always flows smoothly and predictably. Newtonian fluids follow Newton's law of viscosity, meaning the shear stress is directly proportional to the shear rate. This predictable behavior distinguishes them from non-Newtonian fluids, which change their viscosity under different forces.