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Old September 25, 2012, 10:57 PM   #74
Frank Ettin
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Join Date: November 23, 2005
Location: California - San Francisco
Posts: 6,647
Quote:
Originally Posted by SRH78
...Work can't be done without energy, period. That is elementary school level science. A bullet in motion has a given amount of energy. That is also elementary school level science. The variables are where and how that energy is used. That is common sense....
Quote:
Originally Posted by tipoc
...We all know that the faster we get a bullet going the more potential damage that bullet can do. It doesn't matter the caliber or the mass...
But this all goes beyond common sense notions. The physics and physiology of bullet performance are much more complex than that.

Look again at post 67 with 481's quote of Duncan MacPherson (with my emphasis added to the McPherson quote);
Quote:
Originally Posted by 481
From the perspective of evaluating/determining which factor is most important in terminal ballistics, I think that Duncan MacPherson, one of my favorite authors on the topic, nails it pretty well here-

Excerpt from "Bullet Penetration"
Quote:
“. . . every now and then someone wants to analyze or think about a problem involving energy, and when they attempt to do this without really understanding energy or other thermodynamic concepts the result is unfortunate. One such problem is the analysis of any of the various aspects of terminal ballistics; some individuals with inadequate technical training and experience have unwisely and unproductively attempted to use energy concepts in the analysis of bullet impact and penetration in soft tissue. (Many others have simply assumed that energy is the dominant effect in Wound Trauma Incapacitation; this assumption is even more simplistic than the attempt to actually analyze the dynamics problem with energy relationships, and is no more successful).

Any attempt to derive the effect of bullet impact in tissue using energy relationships is ill advised and wrong because the problem cannot be analyzed that way and only someone without the requisite technical background would try. Many individuals who have not had technical training have nonetheless heard of Newton’s laws of motion, but most of them aren’t really familiar with these laws and would be surprised to learn Newton’s laws describe forces and momentum transfer, not energy relationships. The dynamic variable that is conserved in collisions is momentum; kinetic energy is not only not conserved in real collisions, but is transferred into thermal energy in a way that usually cannot be practically modeled. The energy in collisions can be traced, but usually only by solving the dynamics by other means and then determining the energy flow.

Understanding energy and how it relates to bullet terminal ballistics is useful even though energy is not a useful parameter in most small arms ballistics work.”
It's not that energy is not a valid evaluative measure- it's just that it is so darned hard to use it in this role.
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