about 40 seconds into that video he asserts the force of the falling top section must be less than its weight? And you fall for that bullshit?
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Perhaps when you understand such basic processes you maybe better equipped to comment on matters of "physics"
There is a Normal Force, N (assuming the laws of physics are not being tampered with) which is counter to the applied force (mg). Their sum equals the net force (ma)
mg-N=ma
rearranging,
N=mg-ma
Video analysis shows the rate of acceleration to be ~0.64g. Sub that into the equation, and one gets:
N=mg-m(0.64g)=mg(1-0.64)= 0.36mg
36% of the upper block's "weight" is the Normal Force's initial response.
Now perhaps it is YOU who doesn't understand what "weight" means in physics.
It is not the same as MASS which is a component of "weight" and Kinetic Energy, Momentum, etc.
As for your experiment, I have one for you.
Go in an elevator (preferably a fast one) with a scale. Stand on it, record the measurement, then press the button to make the elevator go down...
Make note of what your "weight" is during the acceleration phase, okay?
Then come back and tell me about the "physics" I'm not qualified to discuss.
If I understand the video correctly, the argument is that physics precludes the top of the building from crushing the rest of the building (it should have only taken out 12 floors, the video said). Please correct me if I misunderstand.
Because that makes no sense. The structural system was heavily damaged; if it can't bear the load above it, it comes down. If one part comes down, how could any other part bear the load above it, as the load gets progressively heavier and heavier?
Edit: The fact that we have a BA in physics explaining this to us makes me very nervous about its veracity. If this is simple physics, where are all the credible people at?
In order for the load to become "progressively heavier and heavier" it would need to remain solid or cohesive, as in an inelastic collision. I am sure you have seen the great quantity of ejected material (including massive panels) that did not follow this prerequisite.
As well, the columns were only carrying 30% of their capacity under static load.
That means they could have withstood a 300% increase in load without "collapsing" (I am neglecting effects of Young's and Shear Modulus...I don't like fucking around with Tensors, either, in the case of rotational torques. Matrices are a pain in the ass for me still).
Now consider--at the 50th floor--the load capacity for the remaining structure would have been able to withstand (perhaps unrealistically) the static force of 1 1/2 towers (composed of 3 pieces equal to the upper half)!
With the loss of all that material previously, how does one reconcile the continuation of the collapse without some magical "dark matter" coming into the picture?
And remember, the upper block was NOT an equal proportion of the total mass.
It was substantially less. Furthermore, it wasn't shaped like a wedge, so it didn't exactly have any great leverage to augment the force (outside of the ~4 meters it initially fell).
And if one reads the NIST report carefully, one will see they even accommodate the initial damage by (rightfully) accounting for the load transfer via the hat-truss (which did its job very well).
As for the "BA in Physics" making you "nervous", are you any more comfortable knowing that people with less education are running countries (especially the USA) or that a couple dozen PhDs and PEs at NIST did not bother considering High School physics principles in their analysis?
After all, it's "simple"...with all of the effort they put into making computer models and coming up with these fantastic theories about fires and softened columns (which never cooled or transferred their heat), sagging joists, etc., one would think they could at least show how (or WHY) momentum was not conserved post-initiation,
assuming this was a natural, unaided structural failure.
Actually, it reminds me of a joke I saw on a Chemistry (or was it Earth Sciences?) prof's door.
"You know you're a geek if you can do Vector Calculus, but can't remember how to do long-division..." or something to that effect.
Perhaps these "simple" matters aren't "complex" enough for their refined cerebra?
I'm not sure what you mean by "credible" in this case, either. Are you waiting for Richard Feynman to jump out of the grave and wave pieces of rubber dipped in ice-water? There are plenty of physicists and engineers out there saying this stuff. But they don't care about you, so you might have to look for them yourself instead of waiting for them to appear.
By the way, have you found the section in the NIST study that discusses the actual collapse of the towers, not just the initiation?
I can't find that part...
