What type of fluid has viscosity that changes with the shear rate?

What type of fluid has viscosity that changes with the shear rate?

• A. Newtonian fluid
• B. Non-Newtonian fluid
• C. Ideal fluid
• D. Incompressible fluid

Answer: (B)

Viscosity that changes with the rate at which you shear the fluid describes non-Newtonian fluids. In Newtonian fluids, viscosity stays constant no matter how fast you deform the fluid—water and air are classic examples. But in non-Newtonian fluids, the internal structure responds to shear, so viscosity can either decrease (shear-thinning) or increase (shear-thickening) with higher shear rates. For instance, ketchup flows more easily when squeezed (viscosity drops), while cornstarch in water can behave more solid-like when stirred quickly (viscosity rises). An ideal fluid is described as having no viscosity, and an incompressible fluid concerns density staying constant, not how viscosity depends on shear rate. So the best match for a viscosity that changes with shear rate is a non-Newtonian fluid.

Viscosity that changes with the rate at which you shear the fluid describes non-Newtonian fluids. In Newtonian fluids, viscosity stays constant no matter how fast you deform the fluid—water and air are classic examples. But in non-Newtonian fluids, the internal structure responds to shear, so viscosity can either decrease (shear-thinning) or increase (shear-thickening) with higher shear rates. For instance, ketchup flows more easily when squeezed (viscosity drops), while cornstarch in water can behave more solid-like when stirred quickly (viscosity rises). An ideal fluid is described as having no viscosity, and an incompressible fluid concerns density staying constant, not how viscosity depends on shear rate. So the best match for a viscosity that changes with shear rate is a non-Newtonian fluid.