Think About It

While we are on the topic of the North tower, think about what happened about one and a half hours after the "plane" hit--

the top of the building suddenly collapsed, then the whole building crumbled underneath it, resulting in a massive complete collapse of the whole tower, all in a matter of about ten seconds!

Videos of this event can be found here.

The "plane" impacted at about the 97th floor. In a 110 story building, if the weight was divided equally, about 10% of the building's weight was about the impact area. Since towers are built to be stronger at the base, there should be somewhat less weight at the top, so we can safely say the top 12 floors were less than 10% of the total building mass.

Now there is simply no feasible way that the total upper 12 floors will suddenly break off and drop down from fire and damage. If anything, there should be a slow drooping as the fire slowly weakens the steel columns supporting the upper floors (and even then, the drooping should be asymmetric).

Here is the question--

How can a slow moving mass of less than 10% of a structure COMPLETELY AND RAPIDLY break apart the intact remaining 90% of the structure (remember only the top 15 floors were affected by fire, and not all were burning at the same time)???

Can anyone explain this phenomenon, or model it or even give a good analogy for the collapse????

I eagerly await your answer.