ABSTRACT
In this opening chapter we examine the information that sound can provide for us about the medium through which it passes. That issue provides the rationale for acoustic measurements in experimental investigations of fluid properties. It will be addressed under three main headings. First, the speed of sound depends primarily on thermodynamic properties of the fluid and, under favourable conditions, can provide useful and very accurate information about thermodynamic quantities. Second, the absorption of acoustic energy throughout the bulk of a homogeneous fluid depends primarily upon kinetic effects relating to the distribution of energy on a molecular scale and, also under favourable conditions, can provide a measure of one or more time constants characterizing molecular processes. Finally, the reflection of sound waves from a boundary between the fluid and a solid surface is accompanied by phase changes and energy losses that can sometimes be used to infer the shear viscosity and thermal conductivity of the fluid with useful accuracy. We shall examine each of these in turn. In the course of this chapter, a few of the results of later chapters need to be anticipated so that the relations between acoustic quantities and those in which we are ultimately interested may be quantified.
