 Solution

A generalized Newtonian fluid responds instantaneously with stress determined only by the current scalar shear rate. It therefore cannot represent viscoelasticity, including stress relaxation, elastic recoil, memory, and rate-dependent normal stresses. It also cannot represent thixotropy, in which microstructure and viscosity evolve with the duration and history of shearing. Other omitted effects include hysteresis and genuine finite-time yielding.