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| At 0 °C is ρ0 = 1.293 kg/m3, Z0 = 428 N·s/m3, and c0 = 331 m/s At 20 °C is ρ20 = 1.204 kg/m3, Z20 = 413 N·s/m3, and c20 = 343 m/s At 25 °C is ρ20 = 1.184 kg/m3, Z25 = 410 N·s/m3, and c25 = 346 m/s |
| Google is not correct (look at the following link)
http://www.google.com/search?q=speed+of+sound Here is the answer of Google: "Speed of sound at sea level = 340.29 m/s". This is no good answer, because they forgot to tell us the temperature, and the atmospheric pressure "at sea level" has no sense. |
| In SI units with dry air at 20 °C (68 °F), the speed of sound c is 343 m/s. This also equates to 1235 km/h, 767 mph, 1125 ft/s. It makes no sense to give the speed of sound adding the words at the "standard atmosphere at sea level". The temperature is important. Statement: The air pressure p and the density ρ of air are proportional at the same temperature.
That means, the ratio p / ρ is always constant on a high mountain, and even at "sea level". Forget the air pressure, but look accurately at the very important temperature. Adiabatic index or ratio of specific heats κ (kappa) = cp / cv. Generally we take with sufficient accuracy the formula (equation) for the speed of sound in air in m/s vs. temperature  (theta) in °C:
That gives e.g. at = 20 °C a speed of sound c = 331 + 0.6 × 20 = 343 m/s.
With the following formula you can calculate more exactly the speed of sound. Speed of sound  in m/s; temperature in °CThe speed of sound c depends on the temperature of air and not on the air pressure! The humidity of air has some negligible effect on the speed of sound. The air pressure and the density of air (air density) are proportional to each other at the same temperature. It applies always p / ρ = constant. rho is the density ρ and p is the sound pressure.
Look for the answer of the question: "What is the speed of sound?" Speed of sound - temperature matters, not air pressure Density of air (air density) ρ = air pressure p / (gas constant R × temperature in Kelvin) ρ = p / R × T (kg/m³) The individual gas constant for dry air is R = 287,05 J/kg · K Joule J = Newton · Meter = N m and T in Kelvin = °C + 273.15 Atmospheric pressure p0 = 101325 Pa = 1013.25 mbar = 1013.25 hPa and R = 287.05J/kg · K T0 = 273.15 K at 0°C ρ0 = 101325 p / R (287.05 × 273.15) = 1.2923 kg/m³ T20 = 293.15 K at 20 °C ρ20 = 101325 p / R (287.05 × 293.15) = 1.2041 kg/m³ The speed of sound c is is not the sound velocity v. The sound velocity is the particle velocity. |
Table (chart): The impact of temperature
Speed of sound, density of air, specific acoustic impedance vs. temperature
| Temperature of air °C |
Speed of sound c in m/s |
Time per 1 m Δ t in ms/m |
Density of air ρ in kg/m3 |
Acoustic impedance of air Z in N·s/m3 |
| −25 | 315.7 | 3.165 | 1.423 | 449.7 |
| −20 | 318.9 | 3.134 | 1.395 | 445.1 |
| −15 | 322.0 | 3.103 | 1.368 | 440.9 |
| −10 | 325.2 | 3.073 | 1.341 | 436.5 |
| −5 | 328.2 | 3.044 | 1.316 | 432.4 |
| 0 | 331.3 | 3.017 | 1.293 | 428.3 |
| 5 | 334.3 | 2.990 | 1.269 | 424.5 |
| 10 | 337.3 | 2.963 | 1.247 | 420.7 |
| 15 | 340.3 | 2.937 | 1.225 | 417.0 |
| 20 | 343.3 | 2.912 | 1.204 | 413.5 |
| 25 | 346.2 | 2.888 | 1.184 | 410.0 |
| 30 | 349.1 | 2.864 | 1.164 | 406.6 |
| 35 | 352.0 | 2.840 | 1.146 | 403.5 |
Notice: Air pressure p and air density ρ are not the same.
Calculation of the speed of sound in humid air and the air pressure
Calculation of the wavelength of a wave
in air when frequency and temperature is known
In gases, the higher the velocity of sound, the higher the pitch will be, when you sing.
In conventional use and in scientific literature sound velocity is the same as speed of sound or acoustic velocity.
Sound velocity c should not be confused with sound particle velocity v, which is the velocity of the individual particles.
| Approximate speed of sound in common materials |
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| Medium | Speed of sound m/s ft/s |
||
| Air, dry at 20 °C | 343 | 1 125 | |
| Hydrogen at 0 °C | 1 280 | 4 200 | |
| Water at 15 °C | 1 500 | 4 920 | |
| Lead | 2 160 | 7 090 | |
| Concrete | 3 100 | 10 200 | |
| Wood (soft - along the fibre) | 3 800 | 12 500 | |
| Glass | 5 500 | 18 500 | |
| Steel | 5 800 | 19 000 | |
| In a given ideal gas the speed of sound depends only on its temperature. The speed of sound in still air at 0 degrees Celsius is 331.5 m / s. It depends on the temperature and material. Since sound is transferred easily through densely packed molecules, it is faster in denser substances. Thus the speed of sound increases with the stiffness of the material. |
| On the frequent question: "How much is the speed of sound?" must always follow the demand: "At what temperature, please?" Who mentions the barometric pressure, has still something to learn. |
Speed of sound and acoustic velocity
| Speed is the rate of change of distance with time. Velocity is a measure of both speed and direction of a moving object. Velocity is the rate of change of displacement with time. Speed is a distance an object goes, velocity is measurment of speed AND direction. |
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In a given ideal gas the sound speed depends only on its temperature. The speed of sound in still air at 0 degrees Celsius is 331.5 m/s. It depends on the temperature, and the material. Since sound is more easily transmitted between close molecules, it travels faster in the denser substance. Thus the speed of sound increases with the stiffness of the material. |
Really wrong answers at "Yahoo! Answers"
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How does the speed of sound in air depend on air pressure? 1st wrong answer: Best Answer - Chosen by Voters Thinner air has less atoms floating around in it than denser (higher pressure) air. Since sound waves travel faster when unimpeded, less air pressure equates to faster speed due to decreased atmospheric 'viscosity'. 2nd wrong answer: Speed of sound in air is directly proportional to the square root of pressure. The correct answer is: The speed of sound does not depend on air pressure, but on temperature. Air pressure is not the same as density of air. |
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