The phase speed of a sound wave in a compressible fluid if the expansions and compression are assumed to be adiabatic. This speed a is given by the formula
a2 = (cp/cv) RT
where cp and cv are the specific heats at constant pressure and volume, respectively; R is gas constant; and T is the Kelvin temperature. The value of this speed under standard conditions in dry air is 331 meters per second. Compare Newtonian speed of sound.