Newsgroups: alt.games.quake2,rec.games.computer.quake.playing,rec.games.computer.quake.misc,alt.games.quake
Path: deathrow.com!news.webspan.net!newsfeeds.sol.net!wnfeed!worldnet.att.net!4.1.16.34!cpk-news-hub1.bbnplanet.com!news.bbnplanet.com!ix.netcom.com!not-for-mail
From: mumford@netcom.com (mumford)
Subject: Re: Gun specialists? What about *REAL* guns?
Message-ID: <mumfordErqGKG.1ut@netcom.com>
Sender: mumford@netcom11.netcom.com
Organization: Netcom On-Line Services
X-Newsreader: trn 4.0-test63 (15 March 1998)
References: <35334ed9.3100497@news.telia.lt> <353A5359.2100@NO-SPAM.sgi.net> <6hdo6l$n5m$1@hades.csu.net> <353A816C.EA23735A@wam.umd.edu>
Date: Mon, 20 Apr 1998 22:17:04 GMT
Lines: 98
Xref: deathrow.com rec.games.computer.quake.playing:39304 rec.games.computer.quake.misc:27979 alt.games.quake:28406

A while ago, Joe Crouse <jecrouse@wam.umd.edu> begot:
> almost all artilery pieces in the world since the prussian war have had recoiless
>action ( the prussian war was before ww1) there are pleanty of shotguns that have no
>recoil as well as many hand guns. so why no a rail gun

Quoting another person who replied to the same post you did, to get the
reference of how recoilless guns work:
>>What you guys are referring to is called a recoilless rifle, been around
>>since pre-WWII.  What they do is lauch a much greater mass (at a slower
>>velocity) to the rear to counteract the actual projectile.  The 2 kinetic
>>energies cancel each other.  Picture an explosive charge sandwiched between
>>a light and heavy mass.  Of course, anyone to the rear of the gun is toast.

Let's say for argument that the railgun in Q2 launches a 5 gram uranium slug
at 1/10th the speed of light, and that it takes .1 seconds for the slug to go
from 0 velocity to .1c.

acceleration = velocity/time
a = .1c/.1 = 299,792,458 m/s^2
Force = mass*acceleration
F = .005kg * c m/s^2
  = 1,498,962 newtons

(please note that my computations completely disregard relativistic energy
gained by the slug... it would be manifested as a mass increase of the slug
from 5 grams to 5.025 grams)

Remember Newton's Third law:  For every action, there is an equal and
opposite reaction.  Thus the amount of Force imparted onto the slug by
the railgun must be the same as the amount of Force imparted onto the
gun by the slug.

Now let's assume our Quake2 guy/gal is a real stud-bunny and can lug around
a 60 kg weapon (~130 lbs... I know this is ridiculous, but remember our hero
can carry around two shotguns [+100 shells], two machine guns [+200 bullets],
a grenade launcher [+100 grenades?], a rocket launcher [+100 rockets], a
hyperblaster [+200 cells?], a railgun [+100 slugs] and a BFG without breaking
a sweat), and that 10 of those kg are devoted to the antirecoil mechanism. 
Let's figure the velocity this 10 kg mass would need to move to achieve no
recoil:

a = v/t = v/.1 m/s^2
F = m*a = 1,498,962 newtons
  = 10*v/.1 = 100*v = 1,498,962 newtons
so
v = 14,989 meters/second
  = 9.3 miles/second

It doesn't seem a relastically working mechanism can launch a 10 kg slab at
9.3 miles/second in 0.1 seconds.

Just to point something else out:  the gun appears to be only about 1.5 meters
long, so this 10kg mass would have to be moving at 14,989 m/s within it.  In
other words, it would have to cover the distance of the entire gun in .0001
seconds, 1/1000th of the time it takes to fire the gun.

As a side experiment:
Assume our Quake2 guy weighs 100kg (=~ 220 lbs) and aims the railgun straight
down (and that the railgun has no anti-recoil mechanism).  The reaction force
would be applied to him (and the gun, total mass 160 kg =~ 352 lbs) (well,
realistically the gun would just fly out of his arms, probably ripping his
body apart in the process):

F = m*a = m*v/t
F = 1,498,962 = 160*v/.1 = 1600*v
v = 1,498,962/1600
  = 936 m/s
  = .6 miles/second

In other words, our Quake2 guy (along with his gun) would be launched upwards
at 936 meters per second.  If our Quake2 guy is on a planet with gravitational
acceleration similar to Earth's (a = 9.8 m/s^2):

a = v/t
9.8 = 936/t
t = 936/9.8 = 95.6 seconds
which, using s = 1/2 * a * t^2, would take him to a height of
s = 1/2 * 9.8 * (95.6)^2 = 44,780 meters
  = 27 miles
(assuming a frictionless environment)

(for similar huge numbers based on different masses and speeds, you can visit
the goofs section for the Internet Movie Database's entry for Eraser at
'http://us.imdb.com/More?goofs+Eraser+(1996)')

To summarize:
launching a *5 gram* slug at .1c from the railgun would exert enough force
back on the gun to launch the gun and holder into the air 27 miles.

The railgun is definitely *not* good physics... but it's still a kickass gun.
:)

*whew*... time for me to go play Quake2 :)
-- 
Glenn Lamb - mumford@netcom.com.  Finger for my PGP Key.
Email to me must have my address in either the To: or Cc: field.  All other
mail will be bounced automatically as spam.
PGPprint = E3 0F DE CC 94 72 D1 1A  2D 2E A9 08 6B A0 CD 82
