Perhaps the key point to the entire implausibility of the 'pancake collapse' theory is considering a very old law - conservation of momentum.
Conservation of momentum comes from Newton's first law. A body will remain at rest or travel in uniform motion in a straight line unless acted upon by another force.
Consider the initial collapse of the top sections, which in each case would have the lightest top portion of the building, being the thinnest part of the core. We are expected to believe that as it suddenly (with a flash) lost all its structure and fell onto the floor below, the combined weight of the section above the disintegrated floor lands on the floor below. That causes the floor below to collapse under the strain, and the entire new mass falls onto the next floor. This progression continues neatly all the way down.
That's fine, apart from one very important detail - how does each new floor suddenly assume the accumulated velocity of the falling floors above? We're talking about a progressively heavy core structure (it having been built to bear the weight of the entire structure above, at each stage). So why did it not _substantially_ arrest the downward motion?
As Frank Verismo points out, a great deal of the mass was pulverised in any case, so the full weight of the above sections were dispersed each time a new floor was reached by the downward progression.
How did the really heavy mid to lower sections suddenly start moving at the same pace as the falling upper sections, unless they were offering _virtually no resistance at all_ - unless they were already falling themselves immediately before the progression hit them.
The towers did not come down quite at free-fall speed, but it was not far off it. It was way too close to free-fall acceleration to believe even for a moment than a substantial structure of increasing strength was being crushed by the powdered remains of the floors above.
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If the motion was entirely downwards, with no other force than downward gravity operating after collapse was initiated, why do we see massive steel girders ejected out laterally for hundreds of feet? Why did tiny body parts (sections of finger, etc.) appear on rooftops hundreds of yards away?
In standard building collapses, one would find at least a few things intact. A chair, a monitor, something. How come the biggest items found were fragments of telephone keypads?
Look at the column on the last picture on this page: How did it acquire that precise cut, consistent with a controlled demolition?
http://whatreallyhappened.com/WRHARTICLES/thermite.htm
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But back to conservation of momentum. Inertia dictates that a mass will not suddenly assume the velocity of the moving object falling onto it, even if it is so tenuously structured that a feather falling onto it would initiate its collapse. In this case, we are talking about an increasing substantial structure the further down the building we go. Yet it offered little more resistance than fresh air on the day of 9/11.
