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The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air, is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.91 s or one mile in 4.69 s.
Comparison of the 1962 US Standard Atmosphere graph of geometric altitude against air density, pressure, the speed of sound and temperature with approximate altitudes of various objects. [ 1 ] The U.S. Standard Atmosphere is a static atmospheric model of how the pressure , temperature , density , and viscosity of the Earth's atmosphere change ...
From the speed of sound, the temperature of the air in the planetary boundary layer can be computed. [2] The maximum altitude range of RASS systems is typically 750 metres (2,460 ft), although observations have been reported up to 1.2 km (3,900 ft) in moist air. [3]
TAS can be calculated as a function of Mach number and static air temperature: =, where is the speed of sound at standard sea level (661.47 knots (1,225.04 km/h; 340.29 m/s)),
where a 0 is 1,225 km/h (661.45 kn) (the standard speed of sound at 15 °C), M is the Mach number, P is static pressure, and P 0 is standard sea level pressure (1013.25 hPa). Combining the above with the expression for Mach number gives EAS as a function of impact pressure and static pressure (valid for subsonic flow):
Depending on the aircraft's altitude, sonic booms reach the ground 2 to 60 seconds after flyover. However, not all booms are heard at ground level. The speed of sound at any altitude is a function of air temperature. A decrease or increase in temperature results in a corresponding decrease or increase in sound speed.
It so happens that the speed of sound is a direct function of temperature, so instead of a standard temperature, we can define a standard speed of sound. For subsonic speeds, CAS is calculated as: C A S = a 0 5 [ ( q c P 0 + 1 ) 2 7 − 1 ] {\\displaystyle CAS=a_{0}{\\sqrt {5\\left[\\left({\\frac {q_{c}}{P_{0}}}+1\\right)^{\\frac {2}{7}}-1 ...
Comparison of the 1962 US Standard Atmosphere graph of geometric altitude against air density, pressure, the speed of sound and temperature with approximate altitudes of various objects. [1] Atmospheric temperature is a measure of temperature at different levels of the Earth's atmosphere.