Below is the NIST explanation of the "free fall" so often quoted by some "Truthers." Of course, the "Truthers" never manage to explain how it was accomplished - with the possible exception of Dr. Fetzer's silent mini-nukes theory - but who needs facts in the CT World?
Note that the collapse times were calculated from videos taken outside WTC7 which did not record what was happening inside. Note also that the NIST used the qualifier "essentially" in describing the free fall section of the collapse:
This analysis showed that the 40 percent longer descent time—compared to the 3.9 second free fall time—was due primarily to Stage 1, which corresponded to the buckling of the exterior columns in the lower stories of the north face. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below. This is consistent with the structural analysis model which showed the exterior columns buckling and losing their capacity to support the loads from the structure above. In Stage 3, the acceleration decreased as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below.
Questions and Answers about the NIST WTC 7 Investigation
Note that the collapse times were calculated from videos taken outside WTC7 which did not record what was happening inside. Note also that the NIST used the qualifier "essentially" in describing the free fall section of the collapse:
This analysis showed that the 40 percent longer descent time—compared to the 3.9 second free fall time—was due primarily to Stage 1, which corresponded to the buckling of the exterior columns in the lower stories of the north face. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below. This is consistent with the structural analysis model which showed the exterior columns buckling and losing their capacity to support the loads from the structure above. In Stage 3, the acceleration decreased as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below.
Questions and Answers about the NIST WTC 7 Investigation