sound
sound
A vibration in an elastic medium at a frequency and intensity that is capable of being heard by the human ear. The frequency of sounds lie in the range 20–20 000 Hz, but the ability to hear sounds in the upper part of the frequency range declines with age (see also pitch). Vibrations that have a lower frequency than sound are called infrasounds and those with a higher frequency are called ultrasounds.
Sound is propagated through an elastic fluid as a longitudinal sound wave, in which a region of high pressure travels through the fluid at the speed of sound in that medium. At a frequency of about 10 kilohertz the maximum excess pressure of a sound wave in air lies between 10−4 Pa and 103 Pa. Sound travels through solids as either longitudinal or transverse waves.
