Creative Speculation

1. Newton’s Third Law:
The discusser is not correct in repeatedly claiming that Newton’s third law is violated in the paper and particularly in concluding that the “two-phase collapse scenario is scientifically implausible because it ignores Newton’s third law and the equal but opposite upward force dictated by it.” As explained at the outset in every course on mechanics of materials, this law is automatically satisfied, since all the calculations are based on the concept of stress or internal force, which consists of a pair of opposite forces of equal magnitude acting on the opposite surfaces of any imagined cut through the material or structure. This concept is so central to the discipline of structural mechanics and self-evident to structural engineers that Newton’s third law is never even mentioned in publications.

2. Are the Internal Forces in Upper and Lower Parts of Tower Equal?
Contrary to the discusser’s claim which is based on his understanding of Newton’s third law, these forces are not equal, as made clear by Fig. 2 (g and h) of the original paper. Their difference is equal to the weight of the intermediate compacted layer B plus the inertia force attributable to the acceleration of layer B (for additional accuracy, one may also add the energy per unit height needed for the comminution of concrete and the expelling of air, which are secondary phenomena not taken into consideration in the original paper). When the compacted layer attains a sufficient mass, which occurs after the collapse of only a few stories, this difference becomes very large.
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(Decimation of every argument Gourley made.)
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Closing Comments
Although everyone is certainly entitled to express his or her opinion on any issue of concern, interested critics should realize that, to help discern the truth about an engineering problem such as the WTC collapse, it is necessary to become acquainted with the relevant material from an appropriate textbook on structural mechanics. Otherwise critics run the risk of misleading and wrongly influencing the public with incorrect information.