[Jack Simth]

Originally posted by Aloofi:
Please, somebody tell me that these calculations are wrong or that the numbers in which these calculations are based are wrong.

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The time t required for an object to fall from a height h (in a vacuum) is given by the formula t = sqrt(2h/g), where g is the acceleration due to gravity. Thus an object falling from the top of one of the towers (taking h = 1306 feet and g = 32.174 ft/sec2) would take 9.01 seconds to hit the ground if we ignore the resistance of the air and a few seconds longer if we take air resistance into account. The Twin Towers collapsed in 10 - 15 seconds, close to free fall. Following the start of the collapse the upper floors would have had to shatter the steel joints in all 85 or so floors at the lower levels. If this required only a second per floor then the collapse would have required more than a minute. But the material from the upper floors ploughed through the lower floors at a speed of at least six floors per second. This is possible only if all structural support in the lower 85 or so floors had been completely eliminated prior to the initiation of the collapse. Since the lower floors were undamaged by the plane impacts and the fires, the removal of all structural support in these floors must have been due to some other cause — and the most obvious possibility is explosives. Thus the speed of the collapse (not much more than the time of free fall) is strong evidence that the Twin Towers were brought down in a controlled demolition involving the use of explosives (or some other destructive technology) at all levels.

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It is his assumptions about each floor taking a full second to shatter that is tripping him up, not the rest of the math. The Twin Towers were designed to be structurally effecient, which means there was very little structural redunancy, and no extra support. The floors were supported basically just at the outer edge, with a small amount in the center around the elavator shafts. Each floor consisted of lots of steel, several inches of concrete, and numerous other things.

The kenetic energy of an object falling from a height h and starting from rest (again, in a vacum, like the guy assumed) is m * g * h (mass times gravity times height). Those floors were all very, very heavy. Once they had fallen the height of a single floor they had sufficint kinetic energy to break every remaining floor of the building, even had gravity been cut off at that point. As gravity didn't go away, after two or three floors get crashed the delay due to the rest is negligable.

Edit: Oh, and the upper end of his estimate for the collapse of the towers (15 seconds) is about 1.67 times his calculation for gravity in a vacum, hardly close.

[ May 22, 2003, 16:45: Message edited by: Jack Simth ]