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Speed of sound
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{{Short description|Speed of sound wave through elastic medium}} {{other uses}} [[File:FA-18 Hornet breaking sound barrier (7 July 1999) - filtered.jpg|thumb|right|An [[McDonnell Douglas F/A-18 Hornet|F/A-18 Hornet]] displaying rare localized condensation at the speed of sound]] {{Use dmy dates|date=October 2018}} {{Sound measurements}} The '''speed of sound''' is the distance travelled per unit of time by a [[sound wave]] as it propagates through an [[elasticity (solid mechanics)|elastic]] medium. More simply, the speed of sound is how fast vibrations travel. At {{cvt|20|C|F}}, the speed of sound in air is about {{cvt|343|m/s|ft/s km/h mph kn|0|lk=on}}, or {{val|1|ul=km}} in {{val|2.92|u=s}} or one [[mile]] in {{val|4.69|u=s}}. It depends strongly on temperature as well as the medium through which a [[sound wave]] is propagating. At {{cvt|0|C|F}}, the speed of sound in dry [[air]] (sea level 14.7 psi) is about {{cvt|331|m/s|ft/s km/h mph kn|0}}.<ref>{{cite web |url=https://www.weather.gov/epz/wxcalc_speedofsound |title=Speed of Sound Calculator |publisher=[[National Weather Service]] |access-date=23 July 2021 }}</ref> The speed of sound in an [[ideal gas]] depends only on its temperature and composition. The speed has a weak dependence on frequency and pressure in dry air, deviating slightly from ideal behavior. In colloquial speech, ''speed of sound'' refers to the speed of sound waves in [[Earth's atmosphere|air]]. However, the speed of sound varies from substance to substance: typically, sound travels most slowly in [[gas]]es, faster in [[liquid]]s, and fastest in [[solids]]. For example, while sound travels at {{val|343|u=m/s}} in air, it travels at {{val|1,481|u=m/s}} in [[water]] (almost 4.3 times as fast) and at {{val|5,120|u=m/s}} in [[iron]] (almost 15 times as fast). In an exceptionally stiff material such as [[diamond]], sound travels at 12,000 m/s (39,370 ft/s),<ref>{{Cite web |title=Speed of Sound |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/Soundv.html |access-date=2022-10-24 |author=C. R. Nave |website=HyperPhysics |publisher=Department of Physics and Astronomy, Georgia State University}}</ref>{{snd}} about 35 times its speed in air and about the fastest it can travel under normal conditions. In theory, the speed of sound is actually the speed of vibrations. Sound waves in solids are composed of compression waves (just as in gases and liquids) and a different type of sound wave called a [[S-wave|shear wave]], which occurs only in solids. Shear waves in solids usually travel at different speeds than compression waves, as exhibited in [[seismology]]. The speed of compression waves in solids is determined by the medium's [[compressibility]], [[shear modulus]], and density. The speed of shear waves is determined only by the solid material's shear modulus and density. In [[fluid dynamics]], the speed of sound in a fluid medium (gas or liquid) is used as a relative measure for the speed of an object moving through the medium. The ratio of the speed of an object to the speed of sound (in the same medium) is called the object's [[Mach number]]. Objects moving at speeds greater than the speed of sound (''{{gaps|Mach|1}}'') are said to be traveling at [[supersonic speed]]s. {{Toclimit}}
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