fell at freefall, not near freefall. It fell by almost 2.5 seconds at a rate of free fall, i.e., 9,808 m/s2.If the top had crushed the part bellow, this parts would have reacted with astrength of the same intensity but opposite that would have decreased theacceleration of falling block. As the fall has not decreased, we conclude thatthe interaction force was zero in both directions.An analysis was made by David Chandler andposted on YouTube (http://www.youtube.com/user/ae911truth#p/u/58/CpAp8eCEqNA)using an analysis software in a video made by CBS with a fixed camera pointedalmost perpendicular to the north wall. This software allowed him to obtaindata of distance and time as the building collapsed. From these data it waspossible to calculate the speed (distance / time) of the building fall andacceleration (velocity / time) and build the graph below. The procedure wascalibrated with the heights of two points in the building provided in the NIST reportof August 2008. The measurements indicate that the building fell, for about 2.5seconds in freefall. This is equivalent to eight floors in which the fallingpart did not find any resistance. For other eight floors met minimalresistance, and even then continued to accelerate, but at a lesser rate thanfree fall. Only after these 16 floors fall, began to have significantinteraction with the structure and slowed down.WTC 7- Velocity x Time In the graph we see that the horizontal axis isthe measure of time in seconds and the vertical axis is the measure of velocityin meters per second. The rate is in negative numbers because is downward thesame applies to the acceleration which is the relationship between velocity andtime. We clearly see three stages of acceleration, the first lasting almost onesecond where the building flutters losing rigidity and begins to fall, thesecond is when we have the free fall acceleration, indicated by the blue line,for about 2.5 seconds and a third that lasts slightly less than one secondwhere the rate of acceleration decreases and then it stops.For those who are thinking that the free fall happensonly for 2.5 seconds and not through all the collapse and can be explained tosome extent if we consider the process as a whole make no mistake. The fact isthat even 2.5 seconds of free fall is not consistent with any scenarioinvolving natural weakening, bending or crushing because in this scenario therewould be enormous forces of interaction with the structure bellow that wouldslow the fall. Knowing that even in controlled demolitions not enoughstructures are removed to allow free fall, how could a office fire be moredestructive? Adding the support columns removal in sync around the building perimeteras seen by the unevenness of the top, by the abrupt collapse and the immediatetransition to full support for free fallwe concluded that a natural collapse with acceleration of gravity is notpossible . But nevertheless occurred, meaning that it was not a naturalcollapse, other forces were involved, which destroyed the support columns ofWTC 7.David Chandler also has done an analysis of thecollapse of the North Tower (WTC 1) which can be viewed on YouTube (http://www.youtube.com/watch?v=32-Ctx7MhKY). And just as the official explanation for the collapse