They shall be known as Bush's Laws of Motion

[krispos42]

40. I don't see what the problem is.

The impact of the planes ripped apart part of the load-bearing structure in the building. The load was re-distributed to the remains of the structure, creating localized areas of stress that were at or near the ultimate strength of the materials, the concrete and steel.

As the building swayed in wind, as the fire heated the concrete and steel, the structure progressively weakened as more and more joints deformed or failed. The affected area was in the immediate vicinity of the impact site, naturally.

Eventually, the structure in the affected area weakened enough to cause a very rapid chain-reaction failure of the joints, and the part of the building above the affected area tilted and began falling.

A couple of hundred thousand tons of steel and concrete dropped onto the rest of the building, which was unable to cope with the kinetic energy and momentum transfer. Especially when the dropped load isn't hitting even. The top of the bottom part of the building absorbed the full brunt of the equivalent of a supertanker slamming into it, the jolt shattering concrete, twisting and rending steel, and popping welds and rivets. The upper part of the building continues to fall, with the bottom part of the building crunching steadily downward under the accelerating mass of the upper part.

Every second, the enormous momentum and energy of the upper part is crashing into a structure designed only to hold static loads. The structure is continually overwhelmed all the way down to the bedrock by forces dozens or hundreds of times the design load.



It's like a rope breaking under gradually increasing strain. A few fibers might pop, then all of a sudden... catastrophic failure.

On an episode of "Mythbusters" they were trying to find out if you can rip the transmission of a car out by bolting a cable between the rear axle and, say, a telephone pole.

Despite the fact that the cable was plenty strong enough to pick up the car if it was, say, attached to a crane, the car was able to easily break the cable after getting a few dozen yards of acceleration.

There ya go. When static, the structure of the WTC towers was plenty strong enough to hold the weight. Add motion, and all bets are off.