10 Acoustics and Ultrasonics

A mode of collective behavior within fluids and solids is the ordered patterns of sound waves that result from the compressibility of materials. We know that sound is tremendously important to human communication and has a wide range of technological applications. How are sound waves produced, detected, and measured? What are the scales of position, velocity, pressure, and density variations and how are they related to one another? What determines the velocity of sound waves? What are important effects that occur at different frequencies and wavelengths? What are interesting and useful manifestations of wave-like properties such as a superposition, interference, and diffraction? What happens to sound waves at the interface between different materials? How do we describe, measure, and use sound scattering from objects? (Bats seem to have evolved with a good ability to do this!) What are the special aspects of sound that apply to human sense of hearing and to the aesthetics of musical instruments? Can sound be used to change or control the behavior of materials? What happens when we make sound waves very intense?

Image attribution: Georg Wiora (Dr. Schorsch), CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons