sound, any disturbance that travels through an elastic medium such as air, ground, or water to be heard by the human ear. When a body vibrates, or moves back and forth (see vibration), the oscillation causes a periodic disturbance of the surrounding air or other medium that radiates outward in straight lines in the form of a pressure wave. The effect these waves produce upon the ear is perceived as sound. From the point of view of physics, sound is considered to be the waves of vibratory motion themselves, whether or not they are heard by the human ear.
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