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Old 19th June 2007, 04:50 PM   #62
Dave Rogers
Bandaged ice that stampedes inexpensively through a scribbled morning waving necessary ankles
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Join Date: Jan 2007
Location: Cair Paravel, according to XKCD
Posts: 30,810
Originally Posted by JJM 777 View Post
The top of the building fell through the entire building, rather than falling aside. It would be interesting to test the mechanisms of these two theories with a model of adequate size, e.g. 10% of the original. Otherwise I guess that I will never firmly believe how it works, until I see how it works.
Right, time for a tutorial on scaling. Let's make a 10% sized model of WTC2. It will have columns 10% of the stiffness (scales as area divided by length), but wind forces will be only 1% of the real ones because wind resistance scales with area. The weight will be only 0.1% of the real one (scales with volume). The fracture energy per floor will be 1% of the real one (scales with column area), but the gravitational potential energy (scales as volume multiplied by height) will be 0.01% of the real one. So energetically a 10% scale model will have a ratio of potential energy to fracture energy - the ratio that determines whether or not it will collapse - 100 times less than the real building. So it won't collapse. Now if we weaken the columns by a factor of 100, it will collapse - but this test is discredited by the truth movement, because we have "tweaked the model to ensure collapse".

Summary: Scale models behave nothing like the real thing. If you won't believe it till you see a scale model collapse, then you won't believe it. Even though it's true.

Inspiring discussion of Sharknado is not a good sign for the audience expectations of your new high-concept SF movie sequel.

- Myriad
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