justforfun ha scritto:

Evidentemente non arrivano nello stesso momento. Per il semplice fatto che abbiamo decine di filmati che dimostrano che non è andata così.

Infatti il NIST dice:

Citazione:

"the structure below the level of collapse initiation offered _____MINIMAL_______ resistance to the falling building mass at and above the impact zone. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that energy through energy of deformation.

resistenza minima, non nulla.

Citazione:

Since the stories below the level of collapse initiation provided _______LITTLE________ resistance to the tremendous energy released by the falling building mass, the building section above came down _______ESSENTIALLY________ in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass.”

little resistance, non nulla.

Essentially significa "praticamente come", ma non significa "in caduta libera".

Altrimenti sarebbe stato "no resistance", "no resistance at all", "---- in free fall".

Credo comunque che non sia il caso di attaccarsi alle parole. La struttura non ha praticamente offerto resistenza al crollo una volta che questo è iniziato (ma non significa resistenza 0). Il crollo è stato comunque più lento di una free fall.

"the structure below the level of collapse initiation offered minimal resistance to the falling building mass at and above the impact zone. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that energy through energy of deformation.

Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass.”

In other words, the momentum (which equals mass times velocity) of the 12 to 28 stories (WTC 1 and WTC 2, respectively) falling on the supporting structure below (which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum) so greatly exceeded the strength capacity of the structure below that it (the structure below) was unable to stop or even to slow the falling mass. The downward momentum felt by each successive lower floor was even larger due to the increasing mass.

From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse. Neither the duration of the seismic records nor video evidence (due to obstruction of view caused by debris clouds) are reliable indicators of the total time it took for each building to collapse completely.