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QuantumPion is offline
Apr26-11, 03:33 PM
P: 733
Quote Quote by RamonaDave View Post
This is a misleading statement. Although I'm not a doctor I believe the reason a bullet or knife, or any penetrating object kills is because they severe major blood vessels and organs and fluids seep into body parts that are not suppose to have said fluid. This leads to infections, loss of volume and shock which are the ultimate cause of death. It's not the "force" of the impact nor pressure at the point of impact that cause one to die. As evidence of this I point to people who walk around with bullets or shapnel in them that can't be removed surgically.

In the past I've usually wondered if its the force or energy of the impact. I have discounted momentum as a modality of damage. Since energy and momentum are made up of the same components (ie mass and velocity). If you think about what happens if you are hit with a baseball bat that is swung in an arc. You can move inside the swing and take the impact away from the head of the bat, even a little bit, you can really reduce the damage done to you by the bat. Since the tangential velocity is proportional to the radius of the arc, the momentum of a point halfway down the bat is half of that at the tip (I'm assuming the bat is rotating around the grip end and not being swung by a human arm which will add lenght to the radius). Yet the kinetic energy is 1/4. Thus small changes in velocity yield big changes in damage.

The reason I ask this question (force vs energy) has to do with acceleration. If the force of a strike is the vehicle for damage then the ability to accelerate a weapon and not the velocity at impact is the critical factor. In that case, Bruce Lee's famous 6 inch punch can cause as much damage as the same punch thrown from 24 inches(assume arm's lenght). If, however, energy is important then the punch thrown from 24 inches, although striking with the same force (assuming uniform acceleration throughout the execution of the punch), will strike with a higher velocity (thus have more kinetic energy) and cause more damage.

Lastly I wonder how much "Jerk" plays into this (da/dt).

I'd be interested to hear from an MD on this.
How is my statement misleading? What do you think is the cause of death due to any other large force? Hitting concrete at terminal velocity? A brick landing on your head?

Anyways, your question has already been answered in this thread. What kills you is stress (force per unit area).