Sound Wave

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Sound Wave

A mechanical disturbance advancing with infinite velocity through an elastic medium and consisting of longitudinal displacements of the medium, i.e., consisting of compressional and rarefactional displacements parallel to the direction of advance of the disturbance; a longitudinal wave. Sound waves are small-amplitude adiabatic oscillations. The wave equation governing the motion of sound waves has the form

Missing Image:img src="SP7_s_files/del.gif"2Missing Image:img src="SP7_s_files/phisms.gif" = (1/c2)(Missing Image:img src="SP7_s_files/partderiv.gif"2Missing Image:img src="SP7_s_files/phisms.gif"/Missing Image:img src="SP7_s_files/partderiv.gif"t2)

where Missing Image:img src="SP7_s_files/del.gif"2 is the Laplace operator, Missing Image:img src="SP7_s_files/phisms.gif" is the velocity potential, c is the speed of sound, and t is the time; the density variations and velocities are small. As so defined, this includes waves outside the frequency limits of human hearing, which limits customarily define sound. Also called acoustic wave, sonic wave. See ultrasonic, infrasonic, pressure wave. </dd>
Gases, liquids, and solids transmit sound waves, and the propagation velocity is characteristic of the nature and physical state of each of these media. In those cases where a steadily vibrating sound generator acts as a source of waves, one may speak of a uniform wave train; but in other cases (explosions, lightning discharges) a violent initial disturbance sends out a principal wave, followed by waves of more or less rapidly diminishing amplitude. [[/a>|/a> ]]


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use