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From: mccolm@ucla-cs.UUCP
Newsgroups: net.games.frp
Subject: Re: Physics in AD&D (Enlarging)
Message-ID: <5457@ucla-cs.ARPA>
Date: Thu, 16-May-85 13:09:37 EDT
Article-I.D.: ucla-cs.5457
Posted: Thu May 16 13:09:37 1985
Date-Received: Wed, 22-May-85 07:49:39 EDT
References: <401@ttidcc.UUCP> <276@wuphys.UUCP>
Reply-To: mccolm@ucla-cs.UUCP (Eric McColm)
Organization: UCLA Computer Science Department
Lines: 58

In article <276@wuphys.UUCP> mike@wuphys.UUCP (Mike Jones) writes:
>> The unshrunk ballista bolts have regained their full size and  mass  (never
>> mind where it was) but only have the kinetic energy of an ordinary crossbow
>> bolt.  They should fall out of the air before they get to the beholder.
>> 
>> The above, of course, assumes conservation of mass  and  energy.  The  real
>> question  is:  are these and other physical properties conserved in a world
>> where magic works?
>> 
>> The Polymath (aka: Jerry Hollombe)
>
>First: Kinetic energy is not conserved in the "real" world.  Why should it be
>       in D&D?
> .....
>Third: Magic need not follow the normal laws of physics.  It must be inter-
>       nally self consistent.  It is therefore much easier if it follows the
>       (self consistant) normal physical laws....
>
>Mike Jones

If you want to try applying some sort of physics to the Enlarge spell, (and
to other shapechanging spells), you have four choices, as I see it:

1) Conserve Velocity across shape- and size-changes.  This is clearly what
   was intended in the AD&D joke books.  But this has a *real* serious
   problem:  let's suppose I shoot an arrow at someone, and then double all
   it's linear dimensions while in flight.  The 8 times more massive arrow
   does an average of 3.5*8=28hp, enough to drop a 6HD monster.  Not bad.

2) Conserve Momentum across shape- and size-changes.  This is even worse,
   because now the small rock that I throw and reduce by 70% will be
   travelling at near 200mph when it hits the target.  And polymorphing
   a charging dragon into a kobold can be humorous when the "kobold"
   digs into the side of a nearby hill at at least mach 1.  Remember to
   duck.

3) Conserve Kinetic Energy across shape- and size-changes.  This is appealing
   to me because kinetic energy is what causes damage in the absense of
   sharp objects.  So the 2kg brick thrown at 10m/s has a K of 10J.
   The .5kg hardball resulting from reducing the brick will be travelling
   at 20m/s, and the 20kg block resulting from *enlarging* the brick will
   travel at 3.1m/s, and all will have a K of 10J, and all will do 1D3 damage.
   But if an object is thrown *over* someone and Enlarged, it could fall out
   of the air onto the poor slob, doing damage based on how far it fell.
   Fortunately, it takes a Victorian physicist (at least) to hit the target.

4) Don't conserve any of the above, and make up something for yourself.
   A ref. in one campaign claimed that Enlarge made things "puffy" (mass
   was conserved).  This applied to inanimate things only, but it avoided
   many problems.  But that didn't mean I had to like it.  My character
   was a magician.
--fini--
Eric McColm
UCLA (oo' - kluh) Funny Farm for the Criminally Harmless
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