Carl John Hess cjhess at
Fri Aug 22 08:40:02 PDT 1997

I would like to address a response to my Force post a few days ago.

> > > Daniel de Lincoln wrote:

> > > Um, force is not relevant here.  Momentum (mv) is the key here
> > > (I believe kinetic energy, 1/2 mvv, is not appropriate, as energy
> > > can be dissipated in a collision).  So adding mass to the projectile
> > > is as effective as adding to the velocity, ceteris paribus.

Force is very relevant here.  It is what you feel when an object comes into
contact with you.  It is a function of the object's mass and acceleration,
the two factors we are talking about manipulating to make siege weapon
ammunition more effective.  These are the same two factors with which we
wrestle every time we swing a sword or thrust a spear.  I agree that
momentum is also a factor, but it is also a function of the object's mass
and acceleration.

Kinetic energy is appropriate.  The kinetic energy generated by a blow is
transferred to your body when that blow comes into contact with it.

You are correct -- all things being equal, adding mass to an object is as
effective as adding to the velocity.  However, since I think that the mass
of a tennis ball is adequate for our purposes, and that adding to that mass
could be harmful to the participants, adding to the velocity is, in my
opinion, the best way to increase the force of an object.

> > > However, the limit on velocity may be a mechanical one based on
> > > the structure of the launcher.  For a sufficiently light projectile,
> > > the arm may accelerate up to N MPH because that's what the rubber
> > > band plus the mass of the arm allow, say.

I agree that there may be mechanical limits on the launcher, but I didn't
completely understand what you were saying in the last bit about the
launcher arm and the rubber band.  I think you meant that if the load is
light enough, there is no limit on how fast the launcher arm would be able
to move.  More or less?

> > > Further, air drag is affected by the density.

True.  Also, surface area, mass, and atmospheres affect drag.

> > > If those weren't factors, and if the launcher added a fixed
> > > momentum (which it presumably doesn't, as I wrote above),
> > > we could launch ping-pong balls that would be as effective as
> > > shot puts -- the ping-pong balls would be going like a bat out of
> > > Hell.

The launcher cannot add a fixed momentum to an object.  It can only
accelerate the object in question.  The object is what carries the kinetic
energy that is to be transferred from the launcher to the target.  If we
were fighting in an vacuum environment, like the Moon, a ping pong ball
*could* be as effective as a shot put.  I can demonstrate this through

Remember the little stone-big stone test Galileo conducted?  They did they
same one on the Moon with a hammer and a feather.  This means that if I
accelerate an object like a ping pong ball (say .02 Kg) at a high rate (say
10,000 meters per second, squared -- damn fast, granted) in a zero drag
environment (like a vacuum) it has just as much Force as accelerating a
shot put (say 8 Kg) at a moderate rate (25 meters per second, squared). 
They are both going to knock you on your ass and make you cough blood.

> > Llygoden Llwyd commented:

> > Not to mention that adding mass to the projectiles is an easy way of
> > range.

Too easy, I think.  It's also an easy way to make injuries more likely. 
Also, as another poster noted, range isn't what's going to win the war. 
Accuracy is the key.

My point?  I would rather folks fooled with the acceleration of siege
ammunition rather than their mass.  I think its more safe.

C. Scipio Cinncinatvs

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