Sound is a vibration in an elastic medium. It is a simple form of mechanical energy, and can be described by the mathematics associated with the generation, transmission, and control of energy.
Almost any moving, vibrating, oscillating, or pulsating object is a potential sound source. Usually, though, vibratory sources radiate enough energy to be audible to humans or felt by them.
Sound waves in air (or other gases or fluids) travel outward from the source, transmitted by air molecules, like a rapidly expanding soap bubble. Any particular group of molecules behaves like a pulsating balloon, moving only slightly, while the wave progresses swiftly to great distances. Transmission (flow), or prevention of transmission of sound, and conversion of sound energy to a nonaudible form are the function of so-called acoustical materials.
