First of all, the mechanism for collapse of the dominoes is so far removed from the issues in the breakup of the structure of a building that it is really of little value. However, out of curiosity, I used Tracker to follow the motion of the collapsing dominoes. The graph on the right of the Tracker window shows y vs t, or in other words vertical position vs time. The fact that the graph is essentially a straight line, with occasional dips, indicates nearly constant velocity motion. The falling domino pile is not accelerating. WTC7 accelerated at absolute freefall for the first 2.5 seconds. The North Tower accelerated downward at 2/3 of g for the entire time the roofline was visible. As explained in my series of articles this can only happen when the structural support is removed by something other than the falling mass to clear the way. If the falling mass were destroying the building it would expend energy and stop accelerating. In fact it has been calculated that if the North Tower started to collapse in the manner NIST claims, the collapse would have been arrested within 1 floor. Nice domino tower, however.