Pressure ripples that we hear, measure, tune and sometimes break the sound barrier with.
How sound is produced and travels, displacement and pressure waves, the speed of sound in solids, liquids and gases (Newton, Laplace, temperature), intensity and decibels, pitch, loudness and quality, interference, organ pipes, measuring the speed of sound, beats, diffraction, the Doppler effect, sonic booms, musical scales and the acoustics of buildings.