The calculation above was done for dry air, and moisture content in the air would be expected to increase the speed of sound slightly because the molecular weight of water vapor is 18 compared to 28.95 for dry air. This leads to a commonly used approximate formula for the sound speed in air:ДЇor temperatures near room temperature, the speed of sound in air can be calculated from this convenient approximate relationship, but the more general relationship is needed for calculations in helium or other gases. 004 kg/mol, so its speed of sound at the same temperature isДoing this calculation for air at 0вЊ gives v sound = 331.39 m/s and at 1вЊ gives v sound = 332.00 m/s. For the specific example of dry air at 20вЊ, the speed of sound in air is 343 m/s, while the rms speed of air molecules is 502 m/s using a mean mass of air molecules of 29 amu.ДЇor helium, Оі = 5/3 and the molecular mass is.

It is interesting to compare this speed with the speed of molecules as a result of their thermal energy. The speed of sound is v sound = m/s = ft/s = mi/hr. Оі = the adiabatic constant, characteristic of the specific gasДЇor air, the adiabatic constant Оі = 1.4 and the average molecular mass for dry air is 28.95 gm/mol.M = the molecular weight of the gas in kg/mol.R = the universal gas constant = 8.314 J/mol K,.

The speed of sound in an ideal gas is given by the relationship

Speed of sound in air