ABSTRACT
This chapter makes an extension of the introductory material of Chapter 2 to the simplest acoustic case of interest to us here, namely the propagation of bulk waves in liquids and gases. Formally, this case is much simpler than that of solids; fluids in equilibrium are always isotropic and only longitudinal (compressional) waves can propagate. Hence, there is no polarization to specify, and scalar wave theory can be applied. From another point of view, ultrasonic waves in liquids are sufficiently different from those in solids that a separate discussion is required. Finally, these results on liquids form a good basis for extending the theory to solids. A good discussion of waves in liquids is given in [6] and [7].
