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A range of different methods exist for the measurement of the speed of sound in air. The earliest reasonably accurate estimate of the speed of sound in air was made by William Derham and acknowledged by Isaac Newton. Derham had a telescope at the top of the tower of the Church of St Laurence in Upminster, England. On a calm day, a synchronized ...
c is the speed of sound in the medium, which in air varies with the square root of the thermodynamic temperature. By definition, at Mach 1, the local flow velocity u is equal to the speed of sound. At Mach 0.65, u is 65% of the speed of sound (subsonic), and, at Mach 1.35, u is 35% faster than the speed of sound (supersonic).
Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 °C (68 °F) air at sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph) using the formula v [m/s] = 331 + 0.6 T [°C].
Mach number is a measure of how fast the airplane is flying relative to the speed of sound. The measurement and indication of airspeed is ordinarily accomplished on board an aircraft by an airspeed indicator (ASI) connected to a pitot-static system .
The SI unit of intensity, which includes sound intensity, is the watt per square meter (W/m 2). One application is the noise measurement of sound intensity in the air at a listener's location as a sound energy quantity. [3] Sound intensity is not the same physical quantity as sound pressure. Human hearing is sensitive to sound pressure which is ...
The speed of acoustic waves depends on the medium's properties, such as density and elasticity, with sound traveling at approximately 343 meters per second in air, 1480 meters per second in water, and varying speeds in solids.
is the standard speed of sound at 15 °C For supersonic airspeeds, where a normal shock forms in front of the pitot probe, the Rayleigh formula applies: C A S = a 0 [ ( q c P 0 + 1 ) × ( 7 ( C A S a 0 ) 2 − 1 ) 2.5 / ( 6 2.5 × 1.2 3.5 ) ] ( 1 / 7 ) {\displaystyle CAS=a_{0}\left[\left({\frac {q_{c}}{P_{0}}}+1\right)\times \left(7\left({\frac ...
In dry air at 20 °C (68 °F), the speed of sound is 343 metres per second (about 767 mph, 1234 km/h or 1,125 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 ...