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From:	Adam Getchell <acgetche@****.UCDAVIS.EDU>
Subject:	Re: Knock Back (Warning: Physics)
Date:	Tue, 11 Apr 1995 22:44:54 -0700

Message no. 1 On Mon, 10 Apr 1995, Paul Jonathan Adam wrote:

> The target doesn't get knocked back because it's only paper :-) If something
> solid and mobile were hit (like a person) they would get a very solid blow
> concentrated in a very small area and acting in a very short time: a very
> high impulse offering a good chance of knocking them back or down. By no
> means guaranteed, though.

No.
As far as knock down is concerned, momentum transfer is the key.
Momentum is mass * velocity. All momentum equations are variations of
m1*v1+m2*v2=mfinal*vfinal (this case is for a perfectly inelastic
collision, where mfinal = m1+m2, such as bullet m1 sticking in person m2.
Yes, there are energy loss terms and so forth but the above is essentially
correct).
What you are using is a modified form of Newton's Third Law. It
is talking about Force in terms of the change in momentum:

F = dp/dt, where p = momentum.

This is really a partial differential equation but only in ususual
cases does mass change, hence dp/dt is approximated by m*dv/dt. In any
case, the modified formula is delta p = F * delta t, which is an
approximation (an inexact differential, technically). The product F *
delta t is usually called the "impulse". Yes, you will produce a large
change in momentum if you have a high force (not pressure, hence the area
of impact is irrelevant) and a *long* amount of time.
But your momentum is still constrained by mass * velocity.
Bullets have low changes of momentums, high Forces and short times,
obeying the version of Newton's law above. Incidentally, that's how they
get their high pressures: they have very small delta t's when they
transfer energy, and small surface areas. This is why kinetic energy
penetrators are dart-shaped (pressure being force divided by area).

By the way, the Third Law of Thermodynamics has to do with all
processes being irreversible ones, hence change in Entropy is always
greater than zero, and never negative (by the 2nd law or Clausius'
Principle).

> Paul J. Adam paul@********.demon.co.uk

========================================================================
Adam Getchell "Invincibility is in oneself,
acgetche@****.engr.ucdavis.edu vulnerability in the opponent."
http://instruction.ucdavis.edu/html/getchell.html

From:	"St. Jean, Ricky" <stjeanr@*******.CANADOREC.ON.CA>
Subject:	Re: Knock Back (Warning: Physics)
Date:	Wed, 12 Apr 1995 14:36:00 PDT

Message no. 2 > As far as knock down is concerned, momentum transfer is the key.
>Momentum is mass * velocity. All momentum equations are variations of
>m1*v1+m2*v2=mfinal*vfinal (this case is for a perfectly inelastic
>collision, where mfinal = m1+m2, such as bullet m1 sticking in person m2.
>Yes, there are energy loss terms and so forth but the above is essentially
>correct).
> What you are using is a modified form of Newton's Third Law. It
>is talking about Force in terms of the change in momentum:
> F = dp/dt, where p = momentum.

What you are taking into account here is the average effect over the entire
object or being. What you are missing is that the entire momentum is
transferred to a miniscule area. This tiny area may cause the center of
balance to change and redirect the entire momentum of the object. Obejects
travel in a straight line untill they are acted upon by a force. Well this
small force may be enough to redirect the larger forces so they act against
the original momentum. Try pushing someone in the chest, then try it in the
head. Same force different location, different effect.

From:	Gary Carroll <gary@****.COM>
Subject:	Re: Knock Back (Warning: Physics)
Date:	Wed, 12 Apr 1995 12:38:18 -0700

Message no. 3 >Encoding: 19 TEXT
>X-Mailer: Microsoft Mail V3.0
>Date: Wed, 12 Apr 1995 14:36:00 PDT
>Reply-To: Discussion of the Fantasy game ShadowRun
<SHADOWRN@*****.NIC.SURFNET.NL>
>Sender: Discussion of the Fantasy game ShadowRun
<SHADOWRN@*****.NIC.SURFNET.NL>
>From: "St. Jean, Ricky" <stjeanr@*******.CANADOREC.ON.CA>
>Subject: Re: Knock Back (Warning: Physics)
>To: Multiple recipients of list SHADOWRN <SHADOWRN@*****.NIC.SURFNET.NL>
>
>> As far as knock down is concerned, momentum transfer is
the key.
>>Momentum is mass * velocity. All momentum equations are variations of
>>m1*v1+m2*v2=mfinal*vfinal (this case is for a perfectly inelastic
>>collision, where mfinal = m1+m2, such as bullet m1 sticking in
person m2.
>>Yes, there are energy loss terms and so forth but the above is
essentially
>>correct).
>> What you are using is a modified form of Newton's Third
Law. It
>>is talking about Force in terms of the change in momentum:
>> F = dp/dt, where p = momentum.
>
>What you are taking into account here is the average effect over
the entire
>object or being. What you are missing is that the entire momentum is
>transferred to a miniscule area. This tiny area may cause the center of
>balance to change and redirect the entire momentum of the object.
Obejects
>travel in a straight line untill they are acted upon by a force.
Well this
>small force may be enough to redirect the larger forces so they
act against
>the original momentum. Try pushing someone in the chest, then try
it in the
>head. Same force different location, different effect.

OK Great,
I've been enjoying this thread, but lets not loose sight of where
this all started. Unfortunately I am not a Physics minded
individual, so I am finding it difficult translating everything that
was discussed and converting it to a suitable (yet not overbearing)
set of dice rolls (for knockback/knockdown).
Obviously as mentioned with emphasis "surprise" has a great deal to
do with the ability to react and not fall down. Leaving me to
believe we can tie knockdown / knockback to Combat Pool or some
psuedo dice alloated from Combat Pool (logically your using Combat
Pool to dodge the bullet - you shouldn't need to allocate more dice
for knockback / knockdown "possibly the same # of dice you allocated
for dodge"). I also can't think that you should use the whole
number (from the gun power i.e. 9M) as your target #. This is where
I was hoping you Physics type could elaborate. Obvious
considerations: Body, Quickness,maybe Strength anything else??
now where do we go from here...

Thanks Gary C.

From:	Adam Getchell <acgetche@****.UCDAVIS.EDU>
Subject:	Re: Knock Back (Warning: Physics)
Date:	Thu, 13 Apr 1995 02:39:58 -0700

Message no. 4 On Wed, 12 Apr 1995, St. Jean, Ricky wrote:

> What you are taking into account here is the average effect over the entire
> object or being. What you are missing is that the entire momentum is
> transferred to a miniscule area. This tiny area may cause the center of

You do not understand physics. The "area" has absolutely no
bearing upon momentum. There are two variables: mass, and velocity.
"Small forces" do not redirect "larger forces". If you want
to
knock me down, you have to apply enough momentum to overcome mine. It's
that simple. The total momentum of a system does not change with respect
to time. This is called Conservation of Momentum, and it is a
fundamental law of physics. Regardless of whether I use a simple
formulation, such as p1=p2, or a complex Hamiltonian operator upon the
general tensor, this is the basic principle.
You are also mixing in torque. Torque is force times distance.
However, just like in linear physics, it is the angular momentum that is
important in changing rotation of an object, not its energy or torque.
Conservation of Angular Momentum is another basic principle of physics,
and it's almost always true (except in quantum spin violations, or parity
violation). Less solid than Linear Momentum, but equally true from our
standpoint. As far as Quantum Mechanics, though, much tricker.

========================================================================
Adam Getchell "Invincibility is in oneself,
acgetche@****.engr.ucdavis.edu vulnerability in the opponent."
http://instruction.ucdavis.edu/html/getchell.html

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