ABSTRACT
Physically, sound is simply wave energy that propagates in solids, liquids, and gases. For sound to exist there must be a disturbance to a medium, giving rise to the traveling sound waves. The characteristics of sound waves can be visualized by considering those produced by a tuning fork, which is essentially a metal bar bent into a U shape. Nuclear explosions produce infrasound, and after the Nuclear Test Ban Treaty of 1963, infrasound listening stations were set up to detect possible violations. Ultrasonic generators produce high-frequency sound wave pulses that scan a designated region of the body. The speed of sound in a solid or a liquid depends on the elastic modulus and the density of the solid or liquid. Suppose a sound source and an observer are moving away from each other in opposite directions, each at half the speed of sound in air.
