A fluid is desirably viscous if its internal resistance to flow is independent of the external force (ie, shear rate) acting on the fluid. This liquid is named "Newton's liquid" after Sir Isaac Newton.
The viscosity function shows the viscosity at the shear rate. For Newtonian fluids, this function is a straight line (curve 1); see Figure 6.
Typical Newtonian liquids are water or salad oil.
A liquid is non-Newtonian if its viscosity varies with shear rate, and for an exact definition - the apparent viscosity needs to be specified .
Different shear-related fluids behave differently: for some, their viscosity decreases as the shear rate increases (curve 2 | eg yoghurt), while others increase with increasing shear rate increase (curve 3 eg starch solution). The flow behavior of non-Newtonian fluids can be much more complex than these basic examples. For more information, please refer to the " Handbook of Rheology " [4] .
However, shear rate is not the most influential factor. Three factors determine the flow behavior of a substance.
