We now apply this simple model to the WTC collapse. We assume that both
WTC building collapses began with an upper block of nfloors collapsing onto a series of
lower floors as in the “domino effect”. We shall refer to this process as the first stage of
collapse. For this stage, (see equation 1), we have an initial mass nmf falling onto the
floor below and becoming mass (n+1)mf. This new, enlarged, block of floors descends
with velocity v2= {n/(n+1)}v1through a distance hfat which point itstrikes the floor
below and becomes mass (n+2)mf moving at velocity {n/(n+2)}v2, and so on. This
implies a first stage collapse sequence for WTC 1: all floors from 110 to 96 (= 14 floors)
collapse onto floor 95; all these floors collapse onto 94 93 92 and so on to 32
1; for WTC 2 all floors from 110 to 81 (= 29 floors) follow the same sequential process.
At the end of each of these collapse events we envision a second stage of collapse
involving the destruction of the upper block of the WTC buildings: for WTC 1 the 97th
floor, plus all floors above, collapse onto the pile of rubble topped by floor 96; this is
followed by floor 98 (plus all floors above) collapsing onto floor 97 and so on. The 2nd
stage sequence for WTC 1 ends with floor 110 collapsing on to all lower floors. For
WTC 2 the 2ndstage involves floor 82 collapsing onto floor 81, followed by 83, 84, etc,
collapsing on to the pile of rubble until floor 110 collapses onto all lower floors.
