[Marnixvdb]

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basic physics says it is not very likely that a building like the WTC tower collapses in 10seconds total after structural failure.

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Mind you, I haven't taken a physics class, but I would think that several hundred tons of building collapsing and gaining momentum wouldn't take all that long. Why would it take longer after total structural failure if it's caused by an airplane as opposed to demolition?

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The towers collapsed in 10 seconds, which corresponds with the time an object would need to fall down from the height of the building. If a building collapses because of structural failure on the upper or intermediate floors, first the upper part would fall on floor where the support fails. Then the support of a lower floor would fail, the building falls further down, etc. This process gain momentum quickly, but because of the resistance (or "friction") of the underlying structure, it would take more than the freefall time of an object falling down from the same altitude. Maybe if things lined up perfectly the difference would be hard to notice, I don't know enough about it to make an educated guess.

But like I said previously, it's the collapse of building 7 that really puzzles me.