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Re: [Phys-l] Final velocity of bullets



Jack Uretsky said...

I suspect that this question is based upon a misconception.
<snip>
A bullet is normally fired at a velocity far above terminal,
and reaches its target with its velocity still far above terminal.
<snip>

Jack, I think the misconception is yours in assuming this is a "normally
fired" bullet. There is no target. The bullet is not aimed. We're
talking about a "celebratory bullet" or a "raucous-crowd bullet." That
is, we are talking about a bullet fired into the air, nearly straight
up. The question is, when people do stupid things like this (randomly
shooting what is normally a lethal weapon into the air at angles near 90
degrees), is it still lethal? What is the final fate of those random
bullets? Will they kill the person if they accidentally land on a
person? Will they punch a hole in the roof of a building if they land
on a building? What is the typical damage done by a free-falling
bullet?" That's what this is thread is all about. Remarks about
normally fired bullets reaching their target at velocities higher than
free-fall terminal velocity are not addressing the question.

If we want to stick with the topic of discussion, there are a lot of
on-topic questions. For example...

(a) At what elevation must a typical gun be fired such that air friction
reduces the velocity sufficiently that the landing velocity is near
free-fall terminal velocity? I think we are agreed that a bullet fired
straight up will land at terminal velocity. I think we are also agreed
that a bullet fired at steep angle, but not straight up, will land with
some horizontal velocity in addition to terminal vertical velocity. Is
there an angle of launch above which a typical bullet is not lethal.
(And I think we realize this is gun and bullet dependent.)

(b) If the gun barrel is rifled so that the bullet spins around its
velocity's direction, preventing tumbling, how long does the spinning
last? Or stated another way, for a typical rifled gun, is there some
angle of launch above which the bullet is likely to begin tumbling
before it lands?

(c) What if the bullet is indeed fired straight up such that the bullet
does land at terminal velocity? Is that lethal? That is, what is
terminal velocity of a straight-up bullet? (I understand there will be
a range depending on the mass and shape of the bullet, and some might be
lethal and others not. The question is still valid. When someone
parties and shoots a gun straight up, what kind of danger exists? Is
this behavior mildly stupid or grossly stupid?

Incidentally, I remember one of my uncles having a habit of shooting
both barrels of his 12-gauge shotgun into the air at midnight on New
Year's eve. I believe they were ordinary shells. Although this wasn't
a smart idea, as long as he was sober it probably wasn't that dangerous.
If it was dangerous then we would need to outlaw things like pheasant or
duck hunting because the normal operation of firing a shotgun into the
air at a flying bird is going to result in a lot of pellets landing
somewhere, and there could be people there.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu