Grr.
You're going to make me go through the archives, aren't you...
Take a look [link|http://wtc.nist.gov/|here] at the NIST site that documents their study of the incident.
F = m a
The volume of the Twin Towers, like all buildings, is mostly air. The weren't giant solid toothpicks waiting to be toppled over. The force needed to make a building fall over sideways is much, much larger than the force necessary to make it collapse. Remember, the steel and so-forth is specified to have a certain strength based on the expected loads and a safety factor. When the steel weakened due to the fire, what was above was sufficient to make the building collapse. Once the collapse started, the force from the collision of the floors above was more than enough to make the building continue collapsing.
Please don't give the nut-jobs who see a conspiracy under every bush the time of day.
Witnesses are impressionable. Peoples perceptions are not camera snapshots of reality. Have a look at [link|http://www.amazon.com/Mind-Hacks-Tools-Using-Brain/dp/0596007795/ref=pd_bbs_sr_1/102-7586094-2365722?ie=UTF8&s=books&qid=1174501684&sr=8-1|Mind Hacks] if you would like a better indication of how we can fool ourselves.
Thank you.
Cheers,
Scott.
