E. Meyer 151 
Fig. 9.17. Shock waves generated by an imploding bubble, 
about 1 cm in diameter. Following the collapse, this bubble radiates shock waves 
shown in frame 22 in Fig. 9.16, which are strong enough to be visible without 
Schlieren optics just by the shadows they cast. More detail can be seen in 
Fig. 9.17 which shows the results of several series of measurements. It is 
clearly seen that each time many shock waves are radiated from neighboring 
centers in closely succeeding intervals. The same observations are made when 
hot steam is blown into cold water, where the hot steam bubbles collapse [17]. 
9.3.4. Steepening of Shock Waves 
An intense compressional wave has a higher velocity than a weak sound 
wave in water as well as in air; the higher the compression, the higher the 
velocity. In air, one of the main reasons for this effect is the higher tempera- 
ture in the superpressure range. In water, however, the high particle velocity 
plays an important part. For example, with a sound pressure of 5000 atm, the 
corresponding particle velocity is 250 m/sec, which is large relative to the 
velocity .of sound even at the lower compressibility and, therefore, results in 
higher velocity in pressurized water. 
15cm 6cem 8cm 10cm 125cm 15cm 
Distance from sound pressure source 
Shock front development of a pressure 
4 5 sec pulse in water 
discharge current Peakpressure 75 at. 
Fig. 9.18. Variation of shock front with distance from transducer. 
