The subject of rheology is concerned with the study of flow and deformation. From a broad perspective, rheology includes almost every aspect of the study of the deformation of matter under the influence of imposed stress. In other words, it is the study of the internal response of materials to forces. Between the extremes of the conceptual views of the Newtonian fluid and the Hookean solid lie materials of great interest. Commercial interest in synthetic polymeric materials has given the greatest impetus to the science of rheology.