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From: ZnU <znu@znu.dhs.org>
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Subject: Re: A question for those interested in physics...
Date: Thu, 28 Mar 2002 16:50:35 -0500
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In article <a7q9p0$n6or0$2@ID-56786.news.dfncis.de>,
 Edwin <zerg@aiur.org> wrote:

> C Lund <christopher.lund@NOSPAMchello.no> wrote in
> news:christopher.lund-FEA33D.11270526032002@news01.chello.no: 
> 
> > In article <x7Vn8.1094$sO2.220418@news.xtra.co.nz>,
> >  "Robert Bowmaker" <robert.bowmaker@dse.gen.nz> wrote:
> > 
> >> Firing bullets straight up is a common occurence in many situations
> >> (i.e. warning shots, shooting at the sky during a funeral for certain
> >> people etc.) 
> >> 
> >> The question is: What actually happens to the bullet? Does it go into
> >> space? 
> > 
> > Unlikely. I don't think the bullet goes fast enough.
> > 
> >> Does it fall back down?
> > 
> > Yes.
> > 
> >> Does it burn up?
> > 
> > Unfortunatly, no.
> > 
> > Not only does the bullet fall back down, but when it hits the ground, 
> > it's travelling at roughly the same speed as when it left the gun
> > (minus a little for air resistance). I'm pretty sure people have been
> > killed this way.
> 
> No,

This is right.

> the force of gravity acting on a few ounces of lead can't accelerate it 
> to the same velocity it had by being fired out of the gun.  If it could, 
> you'd never be able to fire the bullet straight up. The forces would be 
> equal.

This is entirely wrong. You're right that the bullet wouldn't be moving 
nearly as fast. But it's air resistance that's responsible for the 
slower speed.

Gravity simply applies a constant acceleration. Assuming you're in a 
vacuum, there's no limit (short of c) to the velocity it can impart. Why 
does the bullet leave the gun in the first place? Because gravity can't 
apply acceleration nearly as fast as the gun can. For the tens of 
seconds that it takes gravity to cancel the bullet's initial velocity, 
the bullet continues to move upward.

If you fire a bullet straight up, it will climb to a certain hight. That 
hight is the hight at witch the force of gravity, over time, has applied 
enough acceleration to the bullet to exactly cancel out its upward 
momentum. It continues to apply just as much acceleration once the 
bullet has lost its initial speed. So the bullet will come down at 
exactly the same speed it was fired at. Unless something interferes, 
like a lot of air.

-- 
We still feel that color is hard on the eyes for so long a picture.
       -- Frank S. Nugent of The New York Times
          in his 1939 review of Gone With the Wind