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From: jlg@lanl.ARPA
Newsgroups: net.physics
Subject: Re: A Question on Ballistics
Message-ID: <15686@lanl.ARPA>
Date: Wed, 7-Nov-84 13:39:10 EST
Article-I.D.: lanl.15686
Posted: Wed Nov  7 13:39:10 1984
Date-Received: Sat, 10-Nov-84 03:05:44 EST
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Organization: Los Alamos National Laboratory
Lines: 23

> One thing to keep in mind, though, is that the earth's surface is
> curved. Thus, if fired from a given height, in the time it takes the
> bullet to fall that height because of gravity, it will have travelled
> part of the way along a tangent to the earth, and thus will be a little
> above the earth at this new point. At low speeds, this extra distance
> is negligible. At fast enough speeds, though, the new point could be
> the same height above the ground as the firing point. The result is that
> the bullet goes into orbit. :-)
>   Now, if only we could forget about air resistance...

Speaking of air resistance, there is another effect on the bullet.  Due
to air viscosity there are strong dissipative forces on the bullet which
depend only on the speed of the bullet - not its direction.  The result
is that gravity is opposed by air resistance more for a moving bullet than
for a dropped bullet.  This also is a VERY small effect.

To demonstrate that a fired bullet actually falls as fast as a dropped
object, suspend a metal object from an electro-magnet.  Then aim a
'firearm' (popgun, dart gun, etc.) at the object in such a manner that 
the electro-magnet is turned off when the bullet leaves the gun.  Aim
the gun exactly at the target.  Since both the object and the bullet 
fall the same distance during the flight time of the bullet, the object
will always be hit.