The rate in which the buildings fell was at free fall speed into their own foot print. What this means is controlled demo was used. The free fall speed is because there is nothing under the collapsing levels to stop its rate of falling. Because the way the charges are used they are aimed to destroy the floor underneath the collapsing floor in a speed pattern to keep the building from just falling over from the resistance of the floors underneath still fully intact. That is the entire science of controlled demo and why the buildings taken down by controlled demo fall the way they do. Which why the three towers were taken down by the same its the only way to explain their pattern of collapsing and the free fall rate at which all three came down.