The fluid that becomes less viscous as it is sheared harder is called _________. 

Concept:

The fluid that becomes less viscous as it is sheared harder is known as a pseudo-plastic fluid.

Explanation:

Pseudo-plastic fluids, also known as shear-thinning fluids, exhibit a decrease in viscosity with an increase in shear rate. This behavior is opposite to that of dilatant fluids, which increase in viscosity with an increase in shear rate.

Pseudo-Plastic Fluid:

Pseudo-plastic fluids are non-Newtonian fluids where the shear stress is a non-linear function of the shear rate. Common examples include polymer solutions, paints, and certain types of inks. As the fluid is sheared more vigorously, the internal structure of the fluid breaks down, reducing its viscosity.

Other Fluid Types:

Dilatant Fluid:

Dilatant fluids, or shear-thickening fluids, exhibit an increase in viscosity with an increase in shear rate. These fluids become more viscous as they are sheared harder, which is the opposite behavior of pseudo-plastic fluids.

Thixotropic Fluid:

Thixotropic fluids decrease in viscosity over time when subjected to a constant shear rate. Unlike pseudo-plastic fluids, the reduction in viscosity is time-dependent rather than rate-dependent.

Newtonian Fluid:

Newtonian fluids maintain a constant viscosity regardless of the shear rate. The relationship between shear stress and shear rate is linear.