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detail - problem 3 |
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Freefall -- But Significance Understated |
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The NIST Final Report explained the 2.25-sec freefall resulted in a drop spanning eight stories. No explanation was given as to how the structural components below could have suddenly offered no resistance. At the time NIST was maintining the building collapsed at 40% gravitational acceleration, high school physics teacher David Chandler submitted a graphical analysis of a video showing the collapse. This led to NIST acknowledgement of 100% gravitiational acceleration, which is free fall. An updated analysis by Chandler with more recent information from NIST is available here. |
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To gain an appreciation for eight stories of freefall, consider this figure showing two slices of time. The start of freefall is shown on the left, and the end of freefall on the right. The eight stories are shown as a block near the bottom left. This would be hidden from our view, and we don’t know if it was a block of eight floors as shown, or if the floors with structure removed were distributed in some manner. It’s probably more likely the columns on single floors were taken out every third floor, to leave column segments convenient in length for later removal. After the period of freefall had ended, the remaining upper part of the building continued to accelerate downward, but because of resistance of the lower structure, descended at something less than gravitational acceleration. |
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July 14, 2010 |
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