Editing Sound barrier (section)

{{Short description|Sudden increase of undesirable effects when an aircraft approaches the speed of sound}}
{{distinguish|Noise barrier}}
{{About|the aviation term}}
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[[Image:FA-18 Hornet breaking sound barrier (7 July 1999) - filtered.jpg|right|thumb|U.S. Navy [[McDonnell Douglas F/A-18 Hornet|F/A-18]] transonic pushing into the sound barrier. The supersonic white cloud is formed by decreased air pressure and temperature around the tail of the aircraft (see [[Prandtl–Glauert singularity]]).<ref>{{Cite APOD |date=19 August 2007 |title=A Sonic Boom. |access-date=August 30, 2010}}</ref><ref>[https://web.archive.org/web/20071029222904/http://www.eng.vt.edu/fluids/msc/gallery/conden/mpegf14.htm "F-14 Condensation cloud in action"]. ''web.archive.org''. Retrieved: August 30, 2010.</ref>]]
[[Image:Sound barrier chart.svg|thumb|{{Ordered list|Subsonic|Mach 1|Supersonic|Shock wave}}]]

The '''sound barrier''' or '''sonic barrier''' is the large increase in [[aerodynamic drag]] and other undesirable effects experienced by an [[aircraft]] or other object when it approaches the [[speed of sound]]. When aircraft first approached the speed of sound, these effects were seen as constituting a barrier, making faster speeds very difficult or impossible.<ref>[http://encyclopedia2.thefreedictionary.com/sonic+barrier sonic barrier] {{Webarchive|url=https://web.archive.org/web/20161013094110/http://encyclopedia2.thefreedictionary.com/sonic+barrier |date=2016-10-13 }}. thefreedictionary.com.</ref><ref>[http://www.oxforddictionaries.com/us/definition/american_english/sound-barrier sound barrier] {{Webarchive|url=https://web.archive.org/web/20150411130619/http://www.oxforddictionaries.com/us/definition/american_english/sound-barrier |date=2015-04-11 }}. oxforddictionaries.com.</ref> The term ''sound barrier'' is still sometimes used today to refer to aircraft approaching [[Supersonic speed|supersonic flight]] in this high drag regime. Flying faster than sound produces a [[sonic boom]].

In dry air at 20&nbsp;°C (68&nbsp;°F), the speed of sound is 343 metres per second (about 767&nbsp;mph, 1234&nbsp;km/h or 1,125&nbsp;ft/s). The term came into use during [[World War II]] when pilots of high-speed [[fighter aircraft]] experienced the effects of [[compressibility]], a number of adverse aerodynamic effects that deterred further acceleration, seemingly impeding flight at speeds close to the speed of sound. These difficulties represented a barrier to flying at faster speeds. In 1947, American test pilot [[Chuck Yeager]] demonstrated that safe flight at the speed of sound was achievable in purpose-designed aircraft, thereby breaking the barrier. By the 1950s, new designs of fighter aircraft routinely reached the speed of sound, and faster.{{#tag:ref|See "[[Speed of sound]]" for the science behind the speed called the ''sound barrier'', and "[[Sonic boom]]" for information on the sound associated with supersonic flight.|group=N}}