The observed acceleration, 9.1 m/s2 , if maintained, would bring the roof to the ground in 6.2 seconds, very close to free fall in a vacuum, 6.0 seconds. There is no sign of the slow start that would be expected if collapse was caused by the gradual softening of the steel. The graph above fits the data points closely.
The line is drawn with an equation which assumes constant acceleration 7 and the assumed moment at which the collapse commenced is 0.3 seconds into the displayed elapsed time. As the acceleration is constant the net downward force must have been constant. Gravity is constant which implies that the upward force provided by the structure was also constant. It is inconceivable that fires could heat the structural supports so uniformly throughout the height of the building that the collapse would encounter uniform vertical resistance.
Fires by their very nature tend to creep from place to place as they run out of fuel and move to fresh sources, leaving the burnt out area to cool down. Steel regains strength as it cools. There is also the question of uniformity across the length and breadth of the building.
Again we encounter the problem that fires are not normally uniform. If the entire flammable contents of the building had been ignited simultaneously there might have been a chance of obtaining the required uniform weakening of the steel but this clearly did not occur. It is argued in the official reports 8 that the fires were severe but we have seen from the video and photographs that there was not much fire on the near side. That means that if there had been a severe fire it must have been mainly on the far side and would thus have been supplying a source of heat which was anything but uniform.
This would ensure that the supports on the far side would soften first, which would cause the building to lean away. The centre of gravity would move in that direction which would increase the load on the weaker supports while reducing the load on the stronger supports. Having survived a higher load the near supports could not now buckle so the building would inevitably topple over.
This was not observed: the video shows that the building came straight down with extraordinary precision. The speed of fall, the uniformity of acceleration and the verticality of collapse are not consistent with the effects of fire but are fully consistent with the hypothesis that the building supports were rapidly and completely severed.
No plausible explanation for this other than the use of explosives in a controlled demolition has been presented. The falsity of the three official investigations in denying the use of explosives, given that explosive demolition is so obvious, is prima facie evidence for complicity of some part of the administration of the USA in the events of 9/11 and cries out for review.