nucleus until the environmental pressure has reached a certain value (smaller than 

 the vapor pressure and, in fact, typically negative) characteristic of the individual 

 nucleus (See Section 2). Once the growth has begun, the pressure P at the cavity 

 becomes essentially zero*. The example of Figure 4 rather exaggerates the ordinary 

 extent of the delay of the inception of growth. 



Of special interest is the computation of the motion for situations like that 

 depicted in Figure 3. If the temporal variation of the environmental pressure 



1.0 



1.0 



1^3 



RiFo Fo 



-1.0 



.5 



R 



V R> 



t-to 



R, 



Po 



P 



I 



Figure 4. Computed radial motion and sound pressure for a growing and collapsing vapor cavity. 



encountered by a passing nucleus can be deduced from a knowledge of the velocity 

 and pressure fields in the vicinity of the curved boundary, Eq. (12) can be solved by 

 numerical integration to obtain the radius of the cavity as a function of the time. 

 Plessett [17] has done this and, despite the obvious idealizations introduced, found the 

 computed radial motion to resemble the observed behavior reasonably well. Figure 4 

 shows the results of a typical, though hypothetical, example of such a computation, 



* Note that, to avoid needless repetition throughout the discussion, all pressures are 

 referred to the vapor pressure. 



249 



