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| The '''speed of sound''' varies depending on the medium through which the ] waves pass. It is usually quoted in describing properties of substances |
The '''speed of sound''' varies depending on the medium through which the ] waves pass. It is usually quoted in describing properties of substances (e.g. see the article on ]). | ||
| More commonly the term refers to the speed of sound in ]. In this case the physical properties of the air, its ] and ] for instance, affect the speed. However due to the complex way that all of these factors are interrelated, the speed in fact varies linerarly with temperature. An approximate speed can be calculated from: | More commonly the term refers to the speed of sound in ]. In this case the physical properties of the air, its ] and ] for instance, affect the speed. However due to the complex way that all of these factors are interrelated, the speed in fact varies linerarly with temperature. An approximate speed can be calculated from: | ||
| :v = 331 + (0.6 T), where T is the temperature in degrees Celsius | :v = 331 + (0.6 T), where T is the temperature in degrees ] | ||
| A more accurate expression is | A more accurate expression is | ||
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| :<math>V = (\gamma RT)^{1/2}</math> | :<math>V = (\gamma RT)^{1/2}</math> | ||
| where R is the ] (287 J/ |
where R is the ] (287 J/kgK for air), γ is the ] (1.4 for air) | ||
| and T is the absolute temperature in |
and T is the absolute temperature in ]. In the standard atmosphere, T<sub>0</sub> | ||
| is 288.2 K, giving a value of 340 m/s. | is 288.2 K, giving a value of 340 m/s. | ||
Revision as of 14:59, 24 May 2003
The speed of sound varies depending on the medium through which the sound waves pass. It is usually quoted in describing properties of substances (e.g. see the article on sodium).
More commonly the term refers to the speed of sound in air. In this case the physical properties of the air, its pressure and humidity for instance, affect the speed. However due to the complex way that all of these factors are interrelated, the speed in fact varies linerarly with temperature. An approximate speed can be calculated from:
- v = 331 + (0.6 T), where T is the temperature in degrees Celsius
A more accurate expression is
where R is the gas constant (287 J/kgK for air), γ is the adiabatic index (1.4 for air) and T is the absolute temperature in kelvin. In the standard atmosphere, T0 is 288.2 K, giving a value of 340 m/s.
The speed of sound is typically measured given a "standard atmosphere". Under these conditions the speed of sound is approximately 343 m/s, or 750 miles/hour.
In solids the speed of sound is given by:
- v = (E / ρ), where E is Young's modulus and ρ is density.
Thus in steel the speed of sound is approximately 5100 m/s.
The speed of sound in water is of interest to those mapping the ocean floor. In saltwater, sound travels at about 1500 m/s and in freshwater 1435 m/s. These speeds vary due to pressure, depth, temperature, salinity and other factors.
See also Mach number.