James Newtons Massmind wrote:

> Others have said that the weight of the top floor would accelerate the
> lower floors and account for the rapid fall. That is an interesting
> point, which may very well be correct. I don't know. I would love to
> hear from someone who does. 

If it falls from the top, the weight of the top ceiling crashes on the
floor below. There it "shares" its energy and momentum, and both continue
to fall, however slower as if there were no floor below. And so on. To fall
nearly like free fall, I'm pretty sure the whole steel frame has to crash
at nearly the same time (between all floors). 

> However, from all the videos, it is very clear that it started falling
> from the bottom, not the top. If fires heated the steel, why wouldn't
> the top have fallen first?

Maybe because the load is much higher at the bottom, and a much lower
temperature is needed to soften it to a point where it gives in? But even
then, in order to fall in a time that's close to free fall, the whole steel
frame has to give in at nearly the same time. Which may be possible.

Gerhard

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