- IN THE WAVE ITSELF THERE ARE TEMPERATURE GRADIENTS AND THERE IS INTERNAL HEAT TRANSFER

- THE WAVE DOES NOT HOWEVER EXCHANGE HEAT WITH THE SURROUNDINGS AND CONDITIONS WITHIN THE WAVE CAN THUS BE ASSUMED TO BE ADIABATIC.

- FOR WEAK WAVES, FRICTIONAL LOSSES ARE NEGLIGIBLE AND THE PROCESS CAB ALSO BE ASSUMED TO BE ISENTROPIC.

- FOR IDEAL GASES UNDER ADIABATIC AND ISENTROPIC CONDITIONS

P = Const. r^g                (3.2)

THUS FOR IDEAL GASES, FROM EQUATIONS 3.1 AND 3.2 :

a² = [ �P/�r ]_ISENTR. = g Const. r^g-1 = g ( P/r^g) r^g-1

�   a² = g P/r          (3.3)

- ALSO SINCE FOR IDEAL GASES P = R T

a² = g R T                 (3.4)

- TYPICAL VALUES OF THE SPEED OF SOUND AT 15 ^OC :