This video tracks the motion of the NW corner of Building 7 of the World Trade Center on 9/11 2001. For a period of ~2.5 seconds. This means it was falling through itself for over 100 feet with zero resistance, an impossibility in any natural scenario. This period of freefall is solid evidence that explosives had to be used to bring the building down. In the final draft for public comment (August 2008) NIST denied that WTC7 fell at freefall. In the final report in Nov 2008 they reversed themselves and admitted freefall, but denied its obvious significance.
WTC7 in Freefall: No Longer Controversial
This is a revised analysis of the downward acceleration of the World Trade Center, Building 7, which collapsed in a manner suggestive of controlled demolition on September 11, 2001.
My earlier analysis, which is posted on YouTube under my own name, was based on the best information I had at the time, but I now have been able to improve on my results using new information available in the recently released NIST Final Report on Building 7. Despite the accurate data available to NIST, their final report makes dishonest claims about the rate of fall of the building. I'll come back to the NIST report at the end of this video.
In my earlier video analysis, I used the width of the building, which is known to be one hundred meters, to calibrate the scale of the image. In this remake, I used the vertical spacing of the windows visible as horizontal streaks on the face the building. From this, I was able to identify the 29th floor which is listed in the NIST document as having a height of 683 feet, 6 inches, measuring from some baseline which they don't specify. They have the blueprints; I don't. But I take this measurement to be reliable.
The other measurement they give is the height of the roof line, which they state is 925 feet, 4 inches above their baseline. The difference of these two heights, converted to meters, is the basis for the calibration of this video.
The actual measurements were done exactly as before. The cursor was placed on the corner of the building and marks were placed frame by frame. The built-in functions of the Physics ToolKit software capture the positions and times of these marks in a data table from which it computes and displays various kinds of graphs.
I'm here plotting velocity as a function of time. The slope of this kind of graph gives the acceleration. Notice that the data hovers close to zero for nearly a second and then it drops precipitously. From the moment of the drop, the slope of the line appears essentially constant for about 2.5 seconds. By marking two data points, the program can compute the best straight line to fit the data for the linear portion of the graph. The slope of the line is the acceleration.
Down here at the bottom, the computed acceleration is shown, -9.885 meters per second squared. The minus sign indicates downward acceleration. The acceleration of gravity for New York City is 9.802 meters per second squared, so the measured acceleration is within 1% of the acceleration of gravity. Given the graininess and size of the image, 1% is not a significant difference from the actual acceleration of gravity. So the most accurate way to characterize the result is to say the acceleration of the building is indistinguishable from free fall.
Notice that a little after the 3 second mark on our graph, about 2.5 seconds after the building drops, the acceleration ceases to be uniform. This indicates that the falling building is starting to encounter more resistance. Any measurement of the average acceleration that continues for more than the first 2.5 seconds of fall will show a lower average acceleration masking the fact that for a significant 2.5 seconds the building was in literal free fall.
Freefall can only be achieved if there is zero resistance to the motion. In other words, the gravitational potential energy of the building is not available to crush or deform anything. During freefall, all of the gravitational potential energy of the building is being converted into kinetic energy and nothing else. Any breaking, bending, crushing, or pulverizing of the building components is occurring without the assistance of the free falling portion of the building. Any force the top portion of the building might exert on the lower portion would be reflected in a reaction force that would produce an observable slowing of the rate of fall. A reaction force is observable in this graph only in the last seconds when the velocity strays from the straight line.
Assuming that the descent speed was approximately constant". The assumption is clearly false from even casual observation. However, the fact that they proceed to use a clearly indicates the constant speed reference is a misstatement. They're actually assuming constant acceleration.
More bizarre is the claim that "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". If you start with a 40 percent increase in the time of the fall and work backwards to compute the effective acceleration, their claim is equivalent to saying the acceleration of the building is only 5 meters per second squared, which is 51% of the acceleration of gravity.
Our results, however, clearly show a significant stretch of time in which the acceleration of the building is indistinguishable from the acceleration of gravity itself. In other words, complete free fall. They did not use a method that sampled the position versus time to show the velocity profile as was done here. The NIST report uses only two data points: the supposed start of the collapse and the time the roof line disappears from view. By choosing an early starting time, several seconds prior to the onset of free fall, and computing only the average acceleration between that point and the disappearance of the roofline, they gloss over everything that happened in between.
I'm sure they detected some movement of the roofline at the point where they started the clock as a rationale for choosing that point. Even our data here shows a tiny amount of motion in the first second. But what was going on during this time is qualitatively different from what happened moments later. The event triggering the start of their measurements could more accurately be described as precursor movement.
This is like timing the acceleration of a car in a drag race where the starting light goes on then the driver revs his engine a few times before letting out the clutch. It may be a fair way to penalize a sloppy driver but it doesn't say anything about the acceleration of the car was once it is actually moving.
NIST's method tells us nothing about the nature of the motion itself. They merely assume uniform acceleration over a time interval in which it is clear that the acceleration is not uniform. Mislabeling their assumption to be constant speed indicates sloppy work, but asserting uniform acceleration for an interval where the building sits nearly motionless for several seconds, then drops for several seconds in free fall, is beyond incompetence.
It is a crude, blatant lie.
The average acceleration is a meaningless quantity; it is the instantaneous acceleration that is significant because the acceleration at any moment is an indication of the forces at work. To measure and publish a meaningless average acceleration when sufficient data in a multimillion dollar budget are available to measure the actual velocity profile constitutes either gross incompetence, or an attempt to obfuscate the issue.
This is high school physics we're talking about. If they can't get the high school physics right, what confidence can we have in their multi-colored computer animated whiz-bang simulations to tell us the exact sequence of girder failures without any physical evidence for any of it. I'm a high school teacher. I teach my students better lab practice than NIST demonstrates here.
In this video, I have measured the velocity profile and the instantaneous acceleration of the building with orders of magnitude better precision than NIST, and I did it with zero budget, a free software tool commonly used in high school physics classes and a copy of a video downloaded from the internet.
I know the guys at NIST are not incompetent. What I'm left to conclude is that their only purpose in even mentioning freefall is to muddy the water and derail the discussion. The rate of fall of the building is an embarrassment to the official theory. Freefall is a small detail in the whole complex analysis, but it not a minor issue.
Buildings cannot fall at freefall through themselves because even a weakened building requires energy to break up the pieces, crush the concrete, and push things around. When the falling building pushes things, the fall is not free. The things push back and the reaction forces will measurably slow the descent of the building. This is why one would reasonably expect crumbling structures to come down in a tumbling, halting, irregular manner.
In short, the evidence is clear. We are witnessing not the collapse of a building, but it's demolition, and we have received not a report from an independent scientific investigation but a cover-up by a government agency.
[The WTC7 series has elicited a number of questions from people unclear on the details of how I did the measurements, compared to how NIST did them and how the representatives of NIST described their measurements. I have therefore created a WTC7 Measurement FAQ page. I will also use this FAQ as a place of reference for other questions that arise as well.]