And now, for anyone that's still interested, here's the payoff.
Back when I was getting my pilot's license, an old time mechanical engineer presented me with a gift: How to understand all (OK, almost all) of aerodynamics in simple terms of impulse & momentum. Of little tiny balls called air molecules. It's really cool, really enlightening viewpoint.
This view of collisions closely resembles that explanation. It's simple. And, like all of these moments, it's a big "duh..! Of course..." obvious in retrospect.
And it is the exact reason that Heiwa's "once they become detached and are rubble, they can't exert any force or impact" is utter nonsense.
The forces generated in collisions originate from the acceleration of individual atoms. (You could go smaller, but there's no need.)
Whether or not any particular atom is bound to other atoms is completely irrelevant. There is no weight and no momentum contained within the bonds themselves. (We'll leave QM out of this.)
An individual atom of iron that hits a wall & bounces off delivers precisely the same impulse to that wall as an iron atom inside a bar of steel that hits at the same speed.
All of these collisions are amazingly "peaked" and short duration.
And they all obey the Impulse-Momentum Equation: ∫[F dt] = ∆[m v] , considering m to be the mass of the atom, v its velocity, F to be the force exerted and "dt" to be the very, very brief time duration of the collision.
After assigning these little momentum changes & forces to the individual atoms, it is necessary to add up all of them at each small interval in time to find the total force applied in that interval.
[Note: don't confuse the microscale time interval of the atomic collisions (measured in microseconds) for the macroscale time intervals over which you have to add up all the contributions. The second interval is arbitrary, depending on your desired resolution of the events, and will typically be measured in milliseconds to seconds.
Heiwa said yesterday that "The welded connections actually add 'strength' to part C as all 1000 parts are welded together." This is wrong. Welding (almost invariably) makes parts weaker.
But obviously, something in the structure has changed thru the process of welding.
What has changed is simple. Atoms that are part of the same structure act (ALMOST) in unison. The interatomic forces transmit the external forces applied to the structure to all of the atoms in the structure at the speed of sound in the material. (In steel, this is about 5200 ft/sec. Or about Mach 4.5.). Welded structures are not "stronger" than their components. They have precisely as much momentum & inertia as their individual components. No more. No less.
[Did you get that, Heiwa? Large parts have NO MORE inertia or momentum than an equal mass of smaller parts (aka "rubble".)]
They simply act approximately in unison with all the other atoms of the same part. And when you add up the contributions of all the atoms in that part, the value is high simply because they act in unison.
So, I hope that view of the real world puts to bed Heiwa's "rubble can't generate forces or impacts" nonsense.
There are several more payoffs to looking at the collisions in this way.
One relates to "what, on an atomic level, causes inertial forces & stresses? And how & why do they produce deformations in collisions?"
The second is directly related to the rubble generated in the WTC. And why, in spite of my harping on the issue of "compacting the rubble", it will turn out to not be necessary in order for a crushed down 3 story segment of the towers to deliver a larger impact, force and impulse than the same 3 stories "pre-collapse". Crushing alone will do the trick.
But that one will have to wait. As I've got work to get to.
Later,
Tom
