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Approximation of the speed of sound in dry air based on the heat capacity ratio (in green) against the truncated Taylor expansion (in red) In addition, we switch to the Celsius temperature θ = T − 273.15 K, which is useful to calculate air speed in the region near 0 °C (273 K).
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):
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).
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 ...
Figure 1. Table 1's data in graphical format. Although given as a function of depth [note 1], the speed of sound in the ocean does not depend solely on depth.Rather, for a given depth, the speed of sound depends on the temperature at that depth, the depth itself, and the salinity at that depth, in that order.
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)),
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 ...
Because the temperature of the atmosphere generally decreases with altitude (until the tropopause), the speed of sound also decreases with altitude. (See the International Standard Atmosphere for more on temperature as a function of altitude.) A given airspeed, divided by the speed of sound in that air, gives a ratio known as the Mach number. A ...