The Impact of a Compressible Liquid

Abstract

Prom the point of view of mechanics, a medium is considered a fluid if it is incapable of resisting a shearing deformation in a state of mechanical equilibrium. Therefore it is possible to develop a general approach to the study of both liquids and gas which under normal conditions fit into the above concept of a fluid. Depending on the forces and state of motion of a fluid medium its mechanical behavior will also be dependent on its ability to resist bulk changes in its volume. Our intuitive concept of a gas is that it is relatively easy to change its volume, while a liquid with its denser molecular structure is very resistant to volume changes. In fact this makes very little difference in the general mechanical behavior of these two states of matter, thus in low speed aeronautical applications air is treated as incompressible while the study of underwater acoustics focuses on the creation, transmission and reception of pressure waves in a liquid. Given these considerations it is reasonable to ask why we should consider the study of compressible liquids in distinction from compressible fluids in general? The answer to this arises from another significant property of liquids which have the ability to maintain a surface under normal conditions. Because of this property it is possible to develop a number of mechanically complex situations that depend on the boundary conditions that must be maintained at the liquid surface. In fact this property of the liquid state will play a major role in this work. The ability of a liquid to maintain a distinct surface is crucial to the study of a number of mechanical phenomena in which compressibility plays at most a secondary role.