From: Mike Lorrey (mlorrey@datamann.com)
Date: Fri Sep 14 2001 - 17:54:17 MDT
Doug Jones wrote:
>
> James Rogers wrote:
> >
> > Part of the problem is that you are confusing energy with power. A punch
> > doesn't have a lot of power but it does have lots of energy. A pistol
> > bullet has a moderate amount of power, but minimal energy. Energy is what
> > knocks you on your ass, power is how its delivered.
>
> I'm afraid you're mistaken, James. The terms you need are energy
> (0.5*mv^2) and momentum (mv). A fist carries quite a bit of momentum
> due to its mass, but little energy due to the low velocity. Bullets are
> low mass, high velocity. For example (rough guesstimates):
>
> mass velocity momentum energy
> Fist 1 kg 10 m/s 10 kg-m/s 50 J
> Bullet .003 kg 500 m/s 1.5 kg-m/s 375 J
>
> Thus a blow with a fist or foot is likely to impart substantial momentum
> to the target, while a bullet penetrates and tears it while not causing
> much movement.
And what happens when the bullet hits a kevlar vest? Every time I've
seen someone get hit with a vest on, if they weren't leaning into it,
expecting the hit, they get knocked on their asses (though that depends
on the particular round, of course).
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