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Originally posted by ANOK
Originally posted by PhotonEffect
I've asked ANOK & friends repeatedly, at what floor should the collapse have completely arrested. But I can't seem to get any sort of a straight answer; or even a monkey's guess.
You have, I don't recall.
But who knows? How can anyone answer that question, and why do you think it makes a difference?
I realize you apparently exist for the sole purpose of riding my ass, but all I have to do is scroll past your posts as I encounter them, which isn't difficult. SnowCrash continues his trend of handing you your ass at every turn. You should stop embarrassing yourself, especially if your secret thrill is believing that I'm reading your tripe.
"'There are two ways of doing calculations in theoretical physics,' he said. 'One way, and this is the way I prefer, is to have a clear physical picture of the process you are calculating. The other way is have a precise and self-consistent mathematical formalism. You have neither.'
Originally posted by -PLB-
reply to post by IrishWristwatch
I kind of miss the point of these calculations. What exactly does it matter that in a uniform density distribution the acceleration of an accreting mass converges to a certain value? How is that related to the WTC? It seems to me that, depending on the type of construction, with a building collapse you can have any amount of acceleration, form 0 to g, with g being an asymptote. In case of the WTC tower it turned out to be about 2g/3. (and I also don't understand how density is defined by H/M. Shouldn't that be M/H?).
We are playing semantic games with the word COLLAPSE. But the Laws of Physics do not care about semantics.
Regardless of what destroyed the buildings the Physics Profession has made an ass of itself by not demanding accurate data on the towers.
Originally posted by psikeyhackr
The building may have come down at 2/3rds G but is it possible for the top 15% of any building over 1000 feet tall to force down the structure below at 2/3rds of G?
Originally posted by Darkwing01
Let us be clear here Irish, because you still seem to be under the illusion that you have some claim to being an "expert" of some sort.
You are a layperson too Irish.
You have no standing on your qualifications alone to question David Chandler, never mind Zdenek Bazant.
Originally posted by Darkwing01
Now, I am last person to insist on either qualifications as an arbitrator of debate (...)
Originally posted by -PLB-
reply to post by IrishWristwatch
I kind of miss the point of these calculations. What exactly does it matter that in a uniform density distribution the acceleration of an accreting mass converges to a certain value? How is that related to the WTC?
It seems to me that, depending on the type of construction, with a building collapse you can have any amount of acceleration, form 0 to g, with g being an asymptote. In case of the WTC tower it turned out to be about 2g/3. (and I also don't understand how density is defined by H/M. Shouldn't that be M/H?).
Originally posted by psikeyhackr
But buildings over 1000 feet tall cannot have uniform density.
So playing mathematical games based on that assumption is complete nonsense. It just awes people that are intimidated by the math.
Originally posted by samkent
reply to post by psikeyhackr
We are playing semantic games with the word COLLAPSE. But the Laws of Physics do not care about semantics.
No you are playing semantics.
Originally posted by IrishWristwatch
Edit: the purpose, really, was to show that convergence is not to g. Obviously, the viable range is 0-g, and it isn't going to oscillate, but intuition might lead one to expect the long term limit to be g, since a smaller and smaller percentage of the impacting block mass is swept up. However, more per unit time is swept up. It leads to a balance around g/3. Even with no structural resistance. Even with structural resistance, if the resistance is insufficient to cause arrest (though this hasn't been shown here).
Originally posted by IrishWristwatch
Originally posted by psikeyhackr
But buildings over 1000 feet tall cannot have uniform density.
Absolutely true. It's also true that no physical object is a mathematical point, no 'flat' surface perfectly planar, no oscillation truly linear, and so on. That doesn't stop calculations which use such idealizations from being useful or even accurate when applied to real world problems. I wanted to show the sort of effect momentum exchange alone causes on a simple system. I succeeded.
Originally posted by psikeyhackr
My Python program makes it possible for anyone to create a table with whatever mass distribution they want to see how it affects collapse time. 12 seconds is the minimum with what you would call constant density. Making it bottom heavy increases the time.
Originally posted by -PLB-
Originally posted by psikeyhackr
My Python program makes it possible for anyone to create a table with whatever mass distribution they want to see how it affects collapse time. 12 seconds is the minimum with what you would call constant density. Making it bottom heavy increases the time.
Thats odd, as the calculations are independent of the mass. After all, when you increase the mass of the lower floors, the mass of the top floors increase with the same amount.
One can judge from experiment, or one can blindly accept authority. To the scientific mind, experimental proof is all important and theory is merely a convenience in description, to be junked when it no longer fits. To the academic mind, authority is everything and facts are junked when they do not fit theory laid down by authority. "Doctor Pinero" in Life-Line (1939) by Robert Heinlein
Originally posted by -PLB-
I can see how this applies to your example of a material with a uniform distribution of mass. But I can't see how this is applicable to building collapses.
A building consists mostly of air where acceleration is close to g. So I would expect acceleration converging rather to g than to g/3, if we ignore air resistance.
Just imagine a similar building where the height of the floors is twice as much (2h). That would result in a higher acceleration of the collapse than in the case of a floor with hight h. I don't think the acceleration converges to the same value in both cases, and the further the floors are apart, the close you get to a=g.