ABSTRACT
The majority of known fluids do not exhibit simple Newtonian behaviour in which the viscosity is independent of shear stress and time, but instead exhibit wide and varied rheological properties. Some flow under the influence of gravity, change shape and form while others remain solid at a particular temperature but are liquid and capable of flow at another, such as waxes. Paints, polymers, and many foods retain their form until a sufficient external force is applied causing them to flow. De-icing fluids sprayed onto the wings of commercial aircraft are formulated to remain in place and prevent ice buildup until the aircraft is at the point of takeoff, where the shear force effects of the air passing over the surface are sufficient to remove them. Toothpaste is designed to remain in place on the toothbrush once squeezed from the tube until sufficient shear is applied by the action of cleaning the teeth.
