Robert T. Beyer
Dept. of Phys., Brown Univ., Providence, RI 02912
Traditionally, one has used physical data on fluids to study the propagation of sound in them. However, the opposite is also possible: To use the study of the propagation of sound in a fluid to determine some of its physical properties and its behavior. This was perhaps done for the first time by Einstein (for propagation in gases) in 1920. Today, physical acoustics can be used to gain information about phase transitions in liquid crystals, to study the behavior of mixtures of liquids, and of particles or bubbles in liquids, and in other ways. A review is given of these processes and the ways in which physical acoustics contributes to our knowledge of them.