Perhaps the most important piece of evidence that Building 7 was brought down by controlled demolition is the building’s downward acceleration at absolute free-fall, with sudden onset, for the first few seconds of its collapse.
As documented in the video footage of Building 7’s collapse, the building traveled downward at free-fall acceleration, with sudden onset, for over 100 feet, over a period of approximately 2.5 seconds, based on measurements at the northeast corner of the building. This fact of a period of absolute free-fall was acknowledged by the National Institute of Standards and Technology (NIST) in its final report on Building 7, which was issued in November 2008.1 In its draft report for public comment, in August, 2008, NIST had claimed that Building 7’s downward motion was 40 percent slower than free-fall, a statement which is blatantly untrue.2 NIST changed its characterization of Building 7’s downward motion after a high school physics teacher posted a direct measurement of the motion of the building on YouTube3 and challenged NIST’s assertions in a public comment at NIST’s technical briefing. The measurements incontrovertibly show Building 7 undergoing absolute free-fall.
The significance of free-fall is that a building cannot undergo free-fall if it is meeting any resistance from the structure below it. Any resistance from the structure below will slow the building’s descent.
In an attempt to deny that Building 7 underwent free-fall—before finally acknowledging free-fall in its final report—NIST’s Lead Investigator, Dr. Shyam Sunder, stated at NIST’s technical briefing that, “Free-fall time would be an object that has no structural components below it…[but, referring to Building 7]…There was structural resistance that was provided in this particular case. And you had a sequence of structural failures that had to take place and everything was not instantaneous.”4 Sunder is correctly explaining why free-fall could not happen in the case of a natural collapse. The fact that free-fall did occur is very strong evidence that this was not a natural collapse. NIST’s final report acknowledges 2.25 seconds of free-fall, described as a “more detailed” analysis, but continues incoherently to support its earlier 40% slower than free-fall analysis as well. NIST fails to deal in any way with the plain implications of free-fall.
The fact that Building 7 underwent free-fall means that none of the building’s potential energy was used to crush the structure below it. All of its potential energy was converted directly into energy of motion (kinetic energy), leaving no energy to do anything else. Therefore, the lower section of the building could not have been crushed by the falling section. The destruction of at least 8 stories of the lower section of the building had to have been accomplished by other means to allow the upper section of the building to fall through it in free-fall.
NIST’s theory is that the failure of a single column near the east end of the building caused neighboring columns to fail in a progressive manner. This is contradicted by the observed simultaneous collapse across the entire width of the building, which fell with a level roofline. A progressive collapse mechanism would have led to a progression of failures, visible deformation of the building, and gradual, asymmetrical collapse. This is what NIST’s computer model shows, but it is not what was observed. What we observed was the sudden onset of free-fall across the entire width of the building, which can only be achieved by controlled demolition.
Dr. Sunder was correct to argue that the building should have fallen slower than free-fall if it was a natural collapse. That it fell at free-fall means that it was not.
 National Institute of Standards and Technology (NIST), “Final Report on the Collapse of World Trade Center Building 7,” Washington, DC. November 2008. p.45 http://wtc.nist.gov/NCSTAR1/
 NIST, “Final Report on the Collapse of World Trade Center Building 7 – Draft for Public Comment,” Washington, DC. August 2008. Chapter 3 p.41. http://wtc.nist.gov/media/NIST_NCSTAR_1A_for_public_comment.pdf
 NIST WTC 7 Technical Briefing, August 26, 2008. http://911speakout.org/NIST_Tech_Briefing_Transcript.pdf Transcript p.16