Editing Hydrostatic shock (section)

==Physics of ballistic pressure waves==
[[Image:Harvey Ballistic Pressure Wave.jpg|400px|right|thumb|World War II era ballistic pressure wave measurement. Peak is {{convert|600|psi|abbr=on}}, duration is 0.12 ms.<ref>Medical Department, United States Army. Wound Ballistics in World War II. [ed.] Major James C. Beyer. Washington, D.C. : Office of the Surgeon General, Department of the Army, 1962. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA291697&Location=U2&doc=GetTRDoc.pdf.</ref>]]

A number of papers describe the physics of ballistic pressure waves created when a high-speed projectile enters a viscous medium.<ref name="fn_(30)">{{cite journal |last1=Lee |first1=M. |last2=Longoria |first2=R. G. |last3=Wilson |first3=D. E. |title=Ballistic Waves in High-Speed Water Entry |journal=[[Journal of Fluids and Structures]] |volume=11 |issue=7 |pages=819–844 |year=1997 |doi=10.1006/jfls.1997.0103 |citeseerx=10.1.1.533.7380 |bibcode=1997JFS....11..819L }}</ref><ref name="fn_(31)">{{cite book |last1=Hoover |first1=W. R. |last2=Dawson |first2=V. C. D. |title=Hydrodynamic pressure measurements of the vertical water entry of a sphere |others=U.S. Naval Ordnance Laboratory, White Oak, MD, U.S.A., Tech. Report |pages=66–70 |year=1966 }}</ref><ref name="fn_(32)">{{cite journal |last1=Shi |first1=H. |last2=Kume |first2=M. |title=An Experimental Research on the Flow Field of Water Entry by Pressure Measurements |journal=[[Physics of Fluids|Phys. Fluids]] |volume=13 |issue=1 |pages=347–349 |year=2001 |doi=10.1063/1.1329907 |bibcode=2001PhFl...13..347S }}</ref> These results show that ballistic impacts produce pressure waves that propagate at close to the speed of sound.

Lee et al. present an analytical model showing that unreflected ballistic pressure waves are well approximated by an exponential decay, which is similar to blast pressure waves.<ref name="fn_(30)"/> Lee et al. note the importance of the energy transfer:

{{blockquote| As would be expected, an accurate estimation of the kinetic energy loss by a projectile is always important in determining the ballistic waves.|Lee, Longoria, and Wilson}}

The rigorous calculations of Lee et al. require knowing the drag coefficient and frontal area of the penetrating projectile at every instant of the penetration. Since this is not generally possible with expanding handgun bullets, Courtney and Courtney developed a model for estimating the peak pressure waves of handgun bullets from the impact energy and penetration depth in [[ballistic gelatin]].<ref name="fn_(16)">{{Cite arXiv |eprint = physics/0701267|last1 = Courtney|first1 = Michael|last2 = Courtney|first2 = Amy|title = Ballistic pressure wave contributions to rapid incapacitation in the Strasbourg goat tests|year = 2007}}</ref> This model agrees with the more rigorous approach of Lee et al. for projectiles where they can both be applied. For expanding handgun bullets, the peak pressure wave magnitude is proportional to the bullet's kinetic energy divided by the penetration depth.