ABSTRACT
This chapter deals with propagation of bulk waves in liquids and gases. It is relatively easy to find simple models for the limiting cases of sound propagation in gases and solids. Liquids, however, constitute an intermediate case, and it is more difficult to find a simple model connecting the sound velocity to the molecular constants. Acoustic impedance is a highly useful concept in ultrasonics. The acoustic intensity is the average flux of acoustic energy per unit area per unit time. The monatomic and inert gases have only translational degrees of freedom. Clearly, there is an optimal situation at which the system absorbs a large amount of energy from the field and dumps it efficiently and irreversibly as heat to the surroundings, thus giving a high value of attenuation.
