Free Fall — Part 4

by David Chandler

David Chandler
10 min readApr 26, 2018


Part 1 2 3 4 5 6

In Part 3 we looked at NIST’s Final Report on the Collapse of World Trade Center Building 7; Draft for Public Comment released in August 2008. We turn now to the final report released in November 2008.

During the public comment period after the release of the final draft a number of organizations and individuals, myself included, submitted “requests for correction” heavily criticizing the measurement of the descent of the building that led to the conclusion that it came down 40% slower than free fall. As we saw in Part 3, Steven Jones had elicited a commitment from NIST that they would make a change in the final report due to the erroneous phrase, “Assuming that the descent speed was approximately constant,” when the building was clearly accelerating. A minimal change in the wording was all any of us expected.

However, when the final report was released we were surprised to see a new analysis that acknowledged 2.25 seconds of absolute free fall! I immediately changed the title of my YouTube video that displayed my measurement of free fall to WTC7 in Freefall: No Longer Controversial.

Case closed! Or is it? Upon closer inspection, the new NIST analysis merits more analysis.

Section 3.6 of NIST NCSTAR 1A says,

This is a restatement of the original flawed analysis, which NIST is still defending as valid. NIST does not acknowledge any shortcomings of this approach.

Next, the report says, “A more detailed examination of the same video led to a better understanding of the vertical motion of the building in the first several seconds of descent.” In other words, the new analysis is a supplementary analysis, showing the displacement, velocity, and acceleration of the building rather than just the overall time of fall. The results are presented in an elaborate, cluttered, and deceptive graph:

The first thing you might notice about this graph is it is upside down relative to the graph in the header of this article. That is because the vertical axis of the graph plots the downward velocity. The orientation of the graph is not a substantive issue. I am just explaining this detail for clarity.

The equation of the red regression line in Stage 2 has a slope of 32.196 ft/s² (= 9.813 m/s²), well within the margin of error of absolute free fall. In other words, with this red regression line, NIST does acknowledge free fall. However, there is a period of gradual transition into free fall which NIST calls Stage 1. Keep in mind that NIST is continuing to use Camera 3 (looking upward from West Street) for its measurements. They are also tracking a point near the middle of the roof line where the ambiguity between vertical and lateral motion is maximum (see Part 3). My graph for the NW corner of the building from a level vantage point undergoes a sudden transition from support to free fall. When I repeated NIST’s measurement with the Camera 3 video and a point near the middle of the roof line my results look almost identical to the NIST results, with the erroneous gradual transition leading into free fall. We must conclude that the gradual transition is an artefact of the deceptive camera angle. The bottom line is that the existence of Stage 1, where the building is said to be descending slowly with resistance as the columns progressively buckle, is a fiction.

The rounding of the graph in Stage 1 also accounts for the discrepancy between my measurement of 2.5 seconds of free fall and NIST’s measurement of 2.25 seconds of free fall. If you note where the red regression line crosses the horizontal axis, where the real descent begins, you get 2.5 seconds of free fall just as I did. (The exact duration of free fall is not significant in terms of the implications, but I wanted to point out the source of the discrepancy in case anyone was wondering. I was not just being careless!)

Another point of clarification is the curve NIST uses to interpret the data. They give the equation of the curve, right on the graph, so out of curiosity I plotted it. It is a kind of bell curve. Off hand, it looks like a rather odd way to describe the building collapse data.

This is the interpolation curve NIST used to describe the data. Only the first 5.5 seconds are used for NIST’s graph. It clearly has no physical meaning. It is only a mathematical device to be able to describe scattered data in terms of an explicit function. Beyond the range of fit to the data the curve is meaningless.

The curve has absolutely no physical significance. It is being used merely as an interpolation curve, one that fits the data reasonably well over a certain portion of the domain. I have elsewhere described this as the mathematical equivalent of laying a wet noodle on the data and nudging it around until it fits pretty well. This procedure is not wrong. I am just mentioning it in case some of you might think the curve is the result of some kind of high level analysis. It’s not.

What is wrong with the curve is that it reinforces what is wrong with the data, emphasizing the non-existent gradual transition to free fall. When a level camera perspective is used, eliminating the ambiguous kink in the roof line, the velocity graph takes a sharp turn. One moment the building is stationary, the next moment it is falling at absolute free fall.

Vertical component of velocity vs time as measured from a level perspective, eliminating the deceptive ambiguity of the apparent “kink” in the roof line. Note the sharp transition from support to free fall. The timing interval for this measurement is 0.2 seconds. The transition to free fall happens within one such interval.

When I was in 7th grade one of the science teachers at our school got a grant to put up a fully functioning weather station. I was one of the students trained to use it. One of the skills I learned at that early age was how to read a mercury barometer. I learned that it was important to keep your eye level with the top of the mercury column or you would get false readings. What we have here is analogous. To see whether there is a dip in the roof line you need your eye (or in this case the camera) level with the roof line. NIST had access to the same videos I have, but they chose to use a camera angle that introduces tremendous parallax. One is led to wonder why.

The section concludes,

As stated here, after having made their detour into comments about velocity and acceleration, NIST reverts fully to the original 5.4 second time interval dressed up as a three-stage process. But as we have seen, there is no gradual transition into free fall. If there is no gradual transition there is no Stage 1. If there is no Stage 1, there is no 5.4 second interval which is the linchpin of this analysis. The 5.4 second interval and the “three stages of collapse progression” are simply fabrications.

Another issue is hiding in the language. Laced throughout this section is a repeated phrase, “the north face.”

On one level this phrase seems innocuous. The videos being used for measurements do in fact show the north face of the building. However if you dig deeper you find that the actual claim being made is that only the exterior façade is falling at free fall. A few pages earlier in the report is a table of events including several seconds prior to the start of the visible collapse over which the buckling of core columns propagates from one end of the building to the other. The report claims, “The horizontal progression of buckling core columns was interior to the building and could not have been observed from the street.” Somehow NIST is imagining that the collapse of the interior of the building was decoupled from the exterior walls and occurred earlier than the collapse seen on video. In their account, only the exterior façade remained, which later buckled low in the building resulting in the observed free fall.

The supposed decoupling of the interior collapse from the visible exterior collapse is NIST’s ultimate rationale for accepting the observation of free fall. This claim is both implausible and contrary to the evidence. The WTC 7 Q&A page on the NIST web site makes the claim of decoupling even more explicit. There it says, “WTC 7’s collapse, viewed from the exterior (most videos were taken from the north), did appear to fall almost uniformly as a single unit. This occurred because the interior failures that took place did not cause the exterior framing to fail until the final stages of the building collapse. The interior floor framing and columns collapsed downward and pulled away from the exterior frame.”

How does this contradict reality? Let me count the ways! First, take the time to study a compilation of views of WTC 7’s collapse from different camera angles.

The fall of WTC 7 seen from numerous camera angles. Note that the building retains its stiffness and falls as a unit. Notice the lack of large deformations.

Compare this reality with NIST’s purported reality. Of course, we are seeing the surface of the building, but there are numerous clues about what is going on in the interior.

Notice that the west penthouse (on the right) is supported until about a half second prior to the visible collapse. The columns supporting it must therefore still be present up until that point.

Notice that there was window breakage below the east penthouse when it collapsed into the building several seconds earlier. There was no more window breakage, however, until the start of the visible collapse, which spawned a rash of window breakage under the west penthouse. If surface clues, like window breakage, had accompanied the relatively minor earlier east penthouse collapse, surely a major event, the progressive failure of all the core columns, would have been at least as visible. But that was not the case. After the collapse of the east penthouse there was a quiescent period before the final global collapse.

If the interior columns had buckled they would have pulled the floors down with them, This would have pulled inward on the exterior walls and we would see visible deformations on the surface. The girders could not pull away from the exterior walls, as the NIST Q&A piece claims, because there is no mechanism for the interior to decouple from the exterior walls. The girders directly tie the interior columns to the exterior walls. Note that NIST’s own computer models of the collapse all involved major deformations of the exterior walls, but no such large deformations were seen in the videos of the actual building even as the building was falling.

Exterior deformation seen in NIST’s computer modeling.

When WTC 7 collapsed it gave rise to a huge roiling cloud of dust and debris that flowed down the street as a dense slurry, in a manner some have compared with the ground-hugging pyroclastic flow from a volcano.

Had the interior of the building collapsed earlier than the visible collapse of the exterior walls, as NIST proposes, the large mass of debris inside the building would have easily broken through the walls and the debris clouds would have flowed down the streets prior to the visible collapse of the exterior walls. This did not happen. The collapse of the interior of the building that gave rise to the debris clouds was simultaneous with the visible collapse of the building.

NIST cannot just supplement the errors in the draft report and expect the errors to go away. The draft report is based on the fiction of an early start time for the collapse using a deceptive camera angle to make that determination. After being assailed by its critics (us), the final report conceded the fact of free fall while trying desperately to discount the significance of that finding. The consequences do not go away, however. It is clear that the building fell with a sudden transition to free fall, and that the interior of the building gave way only about a half second early, which is a common demolition technique to pull the building in on itself. The further implication, as discussed previously, is that the building had to have been demolished by an external energy source (explosives).

Something else has been learned from the NIST report, as significant as the physical analysis. What we have seen is that NIST produced a report that is both implausible in general and impossible in detail. They did not do that through incompetence, because the scientists and engineers at NIST are most assuredly not incompetent. NIST has a well-deserved solid reputation for competence and rigor. We must conclude, therefore, that at least under the influence of the Bush administration, a select team within NIST knowingly participated in a cover-up. Since 9/11 was a crime, the NIST report must be considered a criminal cover-up. In fact, since 9/11 provided a false pretext for attacking multiple countries, resulting in the deaths of millions of people, most of them civilians, NIST committed a war crime by participating in covering up a war crime. In a just world, NIST would be held accountable.

Questioning the official story of 9/11 has become taboo in politics, the media, in academia, and in polite society in general. But the events collectively known as 9/11 changed the course of U.S. foreign and domestic policy and impinged on our civil rights and our very identity as a nation. How is it that examining such an event, in careful detail, should be considered taboo if we expect to remain a free society?

And so the rabbit hole opens wide. Before we enter in, let us look briefly at the motion of the Twin Towers. They did not fall at free fall, but let’s take a closer look.

Part 1 2 3 4 5 6



David Chandler

BS physics/MA education/MS math; retired from ~35 years teaching physics, math, & astronomy in high school and college.