A Newtonian fluid is the simplest material flow behaviour one that exhibits a viscosity independent of the applied shear rate or shear StressStress is defined as a level of force applied on a sample with a well-defined cross section. (Stress = force/area). Samples having a circular or rectangular cross section can be compressed or stretched. Elastic materials like rubber can be stretched up to 5 to 10 times their original length.stress.
The materials resistance to flow (viscosity) is constant due to the materials microstructure not affected by the applied shear.