58 



19 

 wave; experiments give a ratio of about one fifth 



The situation Is quite different, however, with regard 



to the impulse of pressure. Assume for simpllalty that r 



is several times amax* ^^^ second term on the right of (10) 



will then at all times be negligible compared with the first, 



and we have 



This will be valid regardless of whether or not r is small 



enough for the non-compressive approximation to be valid at r 



at times near the minimum of ac on traction; it Is only necessary 



that the non-cormre salve approximation be valid at t;i^ and tp. 



I 2 I 



Now a da/dt has Its maximum value, as shown In Appendix 6, when 



-2/5 

 ® = 2 ^max» ^•^•' when the bubble is still fairly large. If 



we take t-, and tg to be the times when a has this value In the 



contracting and expanding phases re soectlvely , (12) will give 



the maximum Impulse of pressure due to the non-compre sslve motion. 



Expressing jja in-terms of more convenient quantities, the 



dt 

 maximum Impulse (12) can be reduced to 



maximum Impulse of pressure 



r 

 This turns out to be of the or-^er of six or eight times the 



Impulse measured in the shock wave by the time the pressure 



l^A.P.Arons and D.r' Yenni?, Rev. Mod. Phys. 20,519 (1948), 



also Volume I, this Gompendlum. 



