> so there is still significant acceleration, approaching free fall
> speeds as the falling mass becomes much greater than the
> mass it is colliding with (which would also be the case if the
> collapse starts at the bottom of the building instead of at the
> top.  Perhaps that explains tower 7's "anomalous" fall speed.)

The footage of WTC7 falling looks like this -

Fires are on the lower floors (the film Painful Deceptions
questions why the sprinklers didn't put them out, as in their
opinion the fires aren't all that big, and certainly were less
big at 9am). There is no smoke around the top of the building

The penthouse and a couple of uppermost floors appear to
collapse first. From then on the building seems to fall down
from the bottom up. It's quite peculiar to see such a huge
building just disappear straight down

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