The roofline of WTC1 (The North Tower) begins dropping with sudden onset and accelerates uniformly downward at about 64% of the acceleration of gravity (g) until it disappears into the dust. This means it is meeting resistance equal to about 36% of its weight. The implication of this, however, is that the force it is exerting on the lower section of the building is also only 36% of its weight. This is much less than the force it would exert if it were at rest. The acceleration data thus prove that the falling top section of the building cannot be responsible for the destruction of the lower section of the building. A complete analysis has been published in the article entitled "Destruction of the World Trade Center North Tower and Fundamental Physics," Journal of 9/11 Studies, Vol 28, Feb 2010: http://journalof911studies.com/volume... (Some calculus and basic physics required.)