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Notice that there is a subsequent, lower, salvo of ejections -- also trailing roiling plumes of particles -- at 13 seconds (lone arrow at lower level), 5 seconds after a prior ejection (4 arrows). This is evidence of a separate subsequent violent outburst of extremely intense energy, which is wholly inconsistent with the "gravitational collapse" portion of the purported-hijacker-blaming official government conspiracy theory of 9/11.

Note also how the ejection corresponding to the upper left arrow runs out of momentum (velocity AND mass!), and stops falling!!! Former-its particles then join the former tower's other remnant nanoparticles in not falling...

So, obviously, Dr. Robert M. Gates, the former Director of the Central Intelligence Agency (CIA) and former Secretary of Defense, is a big liar (or else a tragically huge fool), to say the least.

WTC Free-fall Physics discussion