For me this 5 part series deserves its own thread even though the issue is strongly connected to several other threads in this section of the forum. For example, it is part of the evidence being used in support of the petition for a federal grand jury investigation into 9/11. David Chandler wrote a 5 part series explaining free fall as it pertains to WTC7 on 9/11 and the implications. The first 4 parts have been published and Part 5 is forthcoming. I hope of course the relevant discussion in this thread remains technical as much as possible. I will begin with Part 1, posting excerpts. Free Fall — Part 1 by David Chandler What does it take for a tall building to collapse downward through its own structure at absolute free fall? Galileo demonstrated long ago that any object, of any mass, falling under the influence of gravity alone would accelerate downward at a characteristic rate, which we call the acceleration of gravity, or g. The experimentally determined value of this acceleration varies slightly from one place to another on the surface of the earth. The earth bulges outward slightly at the equator and is flattened at the poles, so gravity is stronger at the poles where one is a little closer to the center of the earth. Similarly, gravity is weaker at higher altitudes. Generally speaking, however, the acceleration of gravity is about 9.8 m/s^2, which means an object will gain 9.8 m/s of speed each second it falls. Starting at rest, at the end of one second it would be moving at 9.8 m/s, at the end of two seconds it would be moving at 19.6 m/s, etc. In physics we say it accelerates at 9.8 [meters/second]/second, which is abbreviated 9.8 m/s^2. (In U. S. Customary units that would be about 32.2 ft/s2^2.) In New York City the acceleration of gravity is about 9.803 m/s^2. Skipping ... Things to note: View the videos on my web site. All four corners of the building start downward within a fraction of a second of each other. The roof line remains essentially level during the entire period of free fall. Whatever is happening to remove resistance is happening across the entire width of the building simultaneously to within a small fraction of a second. Lack of precise synchronization in the removal of support would lead to tumbling. The building is 100 m side to side, and the overall dimensions of the trapezoidal building would essentially cover a football field, overlapping into the end zones. Any coherent theory of the collapse of the building would have to account for how the process happened synchronously over such a large area. One penthouse, on the east side of the building, collapses early, in an event separate from the overall collapse, but the penthouse on the west side of the building (the right) remains supported until about a half second before the overall collapse. It remains partially visible throughout the free fall portion of the collapse. This indicates that the interior support structure is compromised first, but it gives way only a fraction of a second ahead of the perimeter walls. Skipping ... By the way, does this sound like conspiracy theory to you? Notice that I have not theorized, or even hypothesized anything. I am observing and analyzing public information regarding an extremely significant public event, holding it up to the light of day. This is normal curious behavior for a scientist, not political or weird or fringe. Rather, choosing not to observe or not to analyze or not to try to understand such an event for fear of where the evidence might lead, or to insist that only officially sanctioned explanations are to be permitted, or to smear with derogatory labels those who use their own eyes and powers of reason, … that is a political act, and not the kind of politics worthy of citizens of a democratic society. https://medium.com/@davidchandler_61838/free-fall-131a94a1be7e Discussion open.