Proving NIST Right
David Chandler, a high school physics teacher and contributing member of AE911Truth, is the gift that keeps on giving for top 10 mistakes. He has taken a video of WTC 7 falling and identified a short period of time where the building appears to fall at free fall acceleration. He then accuses NIST of covering up this period by their assumption of a constant speed for this collapse.
This attack is based on a draft version of NIST’s final report on WTC 7. Let’s look at what they did. This is from pages 40-41 of the draft report:
NIST was interested in estimating how closely the time for WTC 7 took to fall compared to the descent time if the building were falling freely under the force of gravity (NIST NCSTAR1-9, Chapter 12). Assuming that the descent speed was approximately constant, the two quantities needed for the determinations were (1) a length that some feature of the building descended and (2) the time it took to fall that distance. The chosen feature was the top of the parapet wall on the roofline of the north face. The length was was the difference between the position of the roofline prior to the collapse and the last position the roofline could be observed before it was obstructed by a building in the foreground.
…the actual time for the upper 18 stories to collapse, based on video evidence, was approximately 40 percent longer than the computed free fall time and was consistent with physical principles.
Mr. Chandler took a much grainier version of the same video, loaded it into a computer program, and did as precise a job as he could of measuring the parapet wall’s descent frame by frame. The program he used then could tell him the rate of acceleration at any given moment. This is the chart he uses in his video:
As you can see, Chandler discovers an approximate time of 2.5 seconds where the building appears to be in free fall. Of course there are other places where the building is descending at the same rate of velocity, meaning that it is not speeding up at all, as it would under free fall conditions. But Chandler only focuses on this 2.5 second period. In fact, he stops his charting well before the building disappears from view. Since that last half second shows no acceleration at all, one would expect to see a lot more resistance to the collapse as it continued.
Chandler has not disproved NIST’s calculation at all. In fact, he’s underscored it. Even with this period of free fall, the building itself fell behind the obstruction 40% slower than it would have if the entire building had been subject to free fall acceleration throughout its collapse. The building experienced significant resistance as it fell.
Chandler then pretends that NIST is trying to cover up this section of the collapse. Instead of jumping feet first into his accusation, he would have done better to see if anything else in the draft report could have accounted for these 2.5 seconds.
And there is. Figure 3-14 in the draft report shows Floors 7-14 buckling due to the way the collapse would have propagated. It is this buckling of eight floors that is seen when the building drops down in free fall acceleration for this short part of the collapse.
And NIST realized this, because the final version of this section repeats the initial calculations and then measures much more precisely the complete descent. They found that there was actually a 2.25 second period of virtual free fall, and at the rate it was falling, it would have traveled approximately eight floors during those 2.25. That would be Floors 7-14, precisely.
So far from displaying alleged chicanery by NIST, David Chandler has only helped to confirm their computer modeling with visual analysis. Keep up the good work!