`
`From "Illustrated Dictionary of Science, Andromeda"
`
` Illustrated Dictionary of Science, © Andromeda 1988
`
`Mechanical disturbance, such as a change of pressure, particle displacement or stress, propagated in an
`elastic medium (eg air or water), that can be detected by an instrument or by an observer who hears the
`auditory sensation it produces. Sound is a measurable physical phenomenon and an important stimulus. It
`forms a major means of communication in the form of spoken language, and both natural and manmade
`sounds (of traffic or machinery) contribute largely to our environment. The Ear is very sensitive and will
`tolerate a large range of sound energies, but enigmas remain as to exactly how it produces the sensation of
`hearing. The Greeks appreciated that sound was connected with air motion and that the Pitch of a musical
`sound produced by a vibrating source depended on the vibration Frequency. Attempts to measure the
`velocity of sound in air date from the 17th century. Sound is carried as a longitudinal compressional wave in
`an elastic medium: part of the medium next to a sound source is compressed, but its elasticity makes it
`expand again, compressing the region next to it and so on. The velocity of such waves depends on the
`medium and the temperature, but is always much less than that of light. Sound waves are characterized by
`their wavelength and frequency. Humans cannot hear sounds of frequencies below 16Hz and above 20kHz,
`such sounds being known as infrasonic and Ultrasonic respectively. The sound produced by a Tuning
`Fork has a definite frequency, but most sounds are a combination of frequencies. The amount of motion in a
`sound wave determines its loudness or softness and the intensity falls off with the square of distance from
`the source. Sound waves may be reflected from surfaces (as in an Echo), refracted or diffracted, the last
`property enabling us to hear around corners. The intensity of a sound is commonly expressed in Decibels
`above an arbitrary reference level; its loudness is measured in Phons.
`
`See Sound
`
`
`
` Illustrated Dictionary of Science, © Andromeda 1988
`Persistent URL to the Entry: http://search.credoreference.com/content/entry/andidsci/sound/1
`
`APA
`
`Sound. (1988). In Illustrated dictionary of science, Andromeda. Retrieved from
`http://search.credoreference.com/content/entry/andidsci/sound/1
`
`MLA
`
`"Sound." Illustrated Dictionary of Science, Andromeda. London: Windmill Books (Andromeda
`International), 1988. Credo Reference. Web. 2 May 2014.
`
`Chicago
`
`"Sound." In Illustrated Dictionary of Science, Andromeda. London: Windmill Books (Andromeda
`International), 1988. http://search.credoreference.com/content/entry/andidsci/sound/1 (accessed May
`2, 2014.)
`
`Harvard
`
`1988 'Sound' in Illustrated dictionary of science, Andromeda, Windmill Books (Andromeda
`International), London, United Kingdom. Accessed: 2 May 2014, from Credo Reference
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