ABSTRACT
On the basis of general physical distinctions, matter is commonly divided into three phases: solid, liquid, and gas. Real solid bodies are not absolutely rigid and can be elastically deformed by external forces. The elastic nature of interatomic forces is indicated by simplistically representing them as springs, which, like the forces, resist deformation. Solids and liquids are relatively incompressible and thus have small values of compressibility. A quantity called specific gravity is related to density. It is commonly used for liquids, but also applies to solids. A shear stress cannot be effectively applied to a liquid or a gas because fluids deform continuously in response. Pressure applied to an enclosed fluid is transmitted undiminished to every point in the fluid and to the walls of the container. Theoretical or ideal fluid flow is not characteristic of most real situations, but the analysis of ideal flow provides results that approximate, or generally describe, a variety of applications.
