THE WORK DONE BY AN EXPANDING GAS 848 



Then r-(r 



TO Po W 



">ft 



Hence A - -1- s{i - 



n-lMJn*- 1 



174. T/t FForfc done by an Expanding Gas. If W is the work 

 done in foot-pounds, p is the pressure in Ib. per sq. ft. and v is the 

 volume in cub. ft. 



Then p = -j 



dv 



or W = I dv 



= I p 



Let the gas expand from volume v : to volume v z , the pressure 

 falling in consequence from p l to p 2 . 

 If the law of expansion is pv n = Const 



Then p cv~ n 



r v z 

 and W = cl v~ n dv 



- 



1 - n 



If the law of expansion is pv = Const 



Then p = - 



t; 



and 



= c log e t> 



* 



