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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 10/01/2006 : 20:24:49 [Permalink]
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Let's back up a moment, please, ergo123. Do you accept that there were two airliners, each one hitting one of the Towers? If so, why the need for the discredited demolition job story? If not, is everyone who videoed those planes, nor witnessed them crash, actually just another Administration conspirator? And remember, those witnesses include the possibly millions who saw the second plane crash on live, international TV.
Even if the security firm at the Towers had been corrupted, thousands of employees at the site would have noticed if the walls of their offices were being torn out for weeks on end to get explosive access to load-bearing structures. It's been pointed out here again and again that the vertical load-bearing part of the buildings was the core portion. The horizontal steel in the floors themselves was not critical to the failure.
All that was needed was for the steel in the core to be heated sufficiently to no longer support the huge weight of the floors above. As the Pop Mech article says, "Jet fuel burns at 800° to 1500°F..." and "'Steel loses about 50 percent of its strength at 1100°F,' notes senior engineer Farid Alfawak-hiri of the American Institute of Steel Construction."
If you can't believe what actually happened, remember that Osama bin Laden himself said that he'd only expected about three floors at the points of impact, and the floors above the crashes, to collapse. He was surprised that the whole buildings fell. Osama is a civil engineer by training, yet he had not taken into account the tremendous effect of burning fuel.
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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Dave W.
Info Junkie
USA
26020 Posts |
 Posted - 10/01/2006 : 21:08:17 [Permalink]
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quote:
Originally posted by ergo123
Dave W.: Pancaking. A) there was not enough energy in the upper block of floors to collapse the first impacted floor thus there was not enough energy to start the pancaking process;
I find the assumptions made in the linked paper to be woefully inadequate, and one pivotal consideration is missing from the entire analysis. The author even tries to pass off the concrete pulverization assumption as meaningless, but without it, his total energy balance is positive. And the key point that he seems to neglect is that for a proper analysis of a second collapsed floor, the upper 17 storys will already be moving at 4.8 m/s, and so will impact at 13.3 m/s, and not 8.5 m/s. Since momentum is mass times velocity squared, the second impact will occur with over 5150 MJ of energy, not the measly 2105 MJ of the first impact.quote:
B) even if the upper block of floors did have enough kinetic energy, the time it would take to pancake 90 floors is much greater than 10 seconds;
I don't see why. Assuming that each impact removes 3.7 m/s from the velocity of the top portion of the building (which it won't, since each successive floor would add to the total downward momentum, making each impact's velocity loss less and less), and assuming that the towers had a terminal velocity of only 50 m/s, my calculations run as follows:
-------------------------------------
! ! Vel ! Vel ! ! !
! F# ! Strt ! End ! Time ! Total !
-------------------------------------
! 1 ! 0.0 ! 8.5 ! 0.871 ! 0.871 !
! 2 ! 4.8 ! 13.3 ! 0.409 ! 1.279 !
! 3 ! 9.6 ! 18.1 ! 0.267 ! 1.547 !
! 4 ! 14.4 ! 22.9 ! 0.198 ! 1.745 !
! 5 ! 19.2 ! 27.7 ! 0.158 ! 1.903 !
! 6 ! 24.0 ! 32.5 ! 0.131 ! 2.034 !
! 7 ! 28.8 ! 37.3 ! 0.112 ! 2.146 !
! 8 ! 33.6 ! 42.1 ! 0.098 ! 2.243 !
! 9 ! 38.4 ! 46.9 ! 0.087 ! 2.330 !
! 10 ! 43.2 ! 50.0 ! 0.079 ! 2.410 !
! 11 ! 46.3 ! 50.0 ! 0.077 ! 2.486 !
! 12 ! 46.3 ! 50.0 ! 0.077 ! 2.563 !
! 13 ! 46.3 ! 50.0 ! 0.077 ! 2.640 !
! 14 ! 46.3 ! 50.0 ! 0.077 ! 2.717 !
! 15 ! 46.3 ! 50.0 ! 0.077 ! 2.794 !
! 16 ! 46.3 ! 50.0 ! 0.077 ! 2.871 !
! 17 ! 46.3 ! 50.0 ! 0.077 ! 2.947 !
! 18 ! 46.3 ! 50.0 ! 0.077 ! 3.024 !
! 19 ! 46.3 ! 50.0 ! 0.077 ! 3.101 !
! 20 ! 46.3 ! 50.0 ! 0.077 ! 3.178 !
! 21 ! 46.3 ! 50.0 ! 0.077 ! 3.255 !
! 22 ! 46.3 ! 50.0 ! 0.077 ! 3.332 !
! 23 ! 46.3 ! 50.0 ! 0.077 ! 3.409 !
! 24 ! 46.3 ! 50.0 ! 0.077 ! 3.485 !
! 25 ! 46.3 ! 50.0 ! 0.077 ! 3.562 !
! 26 ! 46.3 ! 50.0 ! 0.077 ! 3.639 !
! 27 ! 46.3 ! 50.0 ! 0.077 ! 3.716 !
! 28 ! 46.3 ! 50.0 ! 0.077 ! 3.793 !
! 29 ! 46.3 ! 50.0 ! 0.077 ! 3.870 !
! 30 ! 46.3 ! 50.0 ! 0.077 ! 3.946 !
! 31 ! 46.3 ! 50.0 ! 0.077 ! 4.023 !
! 32 ! 46.3 ! 50.0 ! 0.077 ! 4.100 !
! 33 ! 46.3 ! 50.0 ! 0.077 ! 4.177 !
! 34 ! 46.3 ! 50.0 ! 0.077 ! 4.254 !
! 35 ! 46.3 ! 50.0 ! 0.077 ! 4.331 !
! 36 ! 46.3 ! 50.0 ! 0.077 ! 4.408 !
! 37 ! 46.3 ! 50.0 ! 0.077 ! 4.484 !
! 38 ! 46.3 ! 50.0 ! 0.077 ! 4.561 !
! 39 ! 46.3 ! 50.0 ! 0.077 ! 4.638 !
! 40 ! 46.3 ! 50.0 ! 0.077 ! 4.715 !
! 41 ! 46.3 ! 50.0 ! 0.077 ! 4.792 !
! 42 ! 46.3 ! 50.0 ! 0.077 ! 4.869 !
! 43 ! 46.3 ! 50.0 ! 0.077 ! 4.945 !
! 44 ! 46.3 ! 50.0 ! 0.077 ! 5.022 !
! 45 ! 46.3 ! 50.0 ! 0.077 ! 5.099 !
! 46 ! 46.3 ! 50.0 ! 0.077 ! 5.176 !
! 47 ! 46.3 ! 50.0 ! 0.077 ! 5.253 !
! 48 ! 46.3 ! 50.0 ! 0.077 ! 5.330 !
! 49 ! 46.3 ! 50.0 ! 0.077 ! 5.406 !
! 50 ! 46.3 ! 50.0 ! 0.077 ! 5.483 !
! 51 ! 46.3 ! 50.0 ! 0.077 ! 5.560 !
! 52 ! 46.3 ! 50.0 ! 0.077 ! 5.637 !
! 53 ! 46.3 ! 50.0 ! 0.077 ! 5.714 !
! 54 ! 46.3 ! 50.0 ! 0.077 ! 5.791 !
! 55 ! 46.3 ! 50.0 ! 0.077 ! 5.868 !
! 56 ! 46.3 ! 50.0 ! 0.077 ! 5.944 !
! 57 ! 46.3 ! 50.0 ! 0.077 ! 6.021 !
! 58 ! 46.3 ! 50.0 ! 0.077 ! 6.098 !
! 59 ! 46.3 ! 50.0 ! 0.077 ! 6.175 !
! 60 ! 46.3 ! 50.0 ! 0.077 ! 6.252 !
! 61 ! 46.3 ! 50.0 ! 0.077 ! 6.329 !
! 62 ! 46.3 ! 50.0 ! 0.077 ! 6.405 !
! 63 ! 46.3 ! 50.0 ! 0.077 ! 6.482 !
! 64 ! 46.3 ! 50.0 ! 0.077 ! 6.559 !
! 65 ! 46.3 ! 50.0 ! 0.077 ! 6.636 !
! 66 ! 46.3 ! 50.0 ! 0.077 ! 6.713 !
! 67 ! 46.3 ! 50.0 ! 0.077 ! 6.790 !
! 68 ! 46.3 ! 50.0 ! 0.077 ! 6.866 !
! 69 ! 46.3 ! 50.0 ! 0.077 ! 6.943 !
! 70 ! 46.3 ! 50.0 ! 0.077 ! 7.020 !
! 71 ! 46.3 ! 50.0 ! 0.077 ! 7.097 !
! 72 ! 46.3 ! 50.0 ! 0.077 ! 7.174 !
! 73 ! 46.3 ! 50.0 ! 0.077 ! 7.251 !
! 74 ! 46.3 ! 50.0 ! 0.077 ! 7.328 !
! 75 ! 46.3 ! 50.0 ! 0.077 ! 7.404 !
! 76 ! 46.3 ! 50.0 ! 0.077 ! 7.481 !
! 77 ! 46.3 ! 50.0 ! 0.077 ! 7.558 !
! 78 ! 46.3 ! 50.0 ! 0.077 ! 7.635 !
! 79 ! 46.3 ! 50.0 ! 0.077 ! 7.712 !
! 80 ! 46.3 ! 50.0 ! 0.077 ! 7.789 !
! 81 ! 46.3 ! 50.0 ! 0.077 ! 7.865 !
! 82 ! 46.3 ! 50.0 ! 0.077 ! 7.942 !
! 83 ! 46.3 ! 50.0 ! 0.077 ! 8.019 !
! 84 ! 46.3 ! 50.0 ! 0.077 ! 8.096 !
! 85 ! 46.3 ! 50.0 ! 0.077 ! 8.173 !
! 86 ! 46.3 ! 50.0 ! 0.077 ! 8.250 !
! 87 ! 46.3 ! 50.0 ! 0.077 ! 8.327 !
! 88 ! 46.3 ! 50.0 ! 0.077 ! 8.403 !
! 89 ! 46.3 ! 50.0 ! 0.077 ! 8.480 !
! 90 ! 46.3 ! 50.0 ! 0.077 ! 8.557 !
------------------------------------- Without a terminal velocity, the entire collapse would take less than half of that 8.557 seconds, but my gut feeling is that the entire building crashing into the basement at over 400 m/s was a bit much.quote:
C) a "pancaked" building does not exhibit pulverized building materials--pancaking occurs when floor supports fail--if energy went into pulverizing building materials, there would not be enough left to knock the floors off their supports and pancake the floors;
The concern is over pulverized concrete, but I question the validity of the assumption made in the analysis. How is it even possible to get from visible clouds of dust to 10% of the concrete being pulverized? Why is there no mention of drywall. I was in office space in the WTC 28 years ago (or so). There was a lot of drywall in the place.quote:
D) pancaked building leave a characteristic in-tact support structure of the buildings supports off of which each floor is knocked yet this was not the case at the WTC.
How many pancaked 100+ story buildings have there been to characterize the behaviour of that architecture? In other words, your assertion doesn't appear to be supported.quote:
I'm just questioning how the collapse managed to defy the laws of physics...
No, you appear to be assuming that a single analysis is correct, when even this layman sees big holes in it. Do you have any other, independent evidence that anything about the collapse defies the laws of physics, or was that your best shot? |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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ergo123
BANNED
USA
810 Posts |
Posted - 10/01/2006 : 21:27:48 [Permalink]
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Halfmooner: I accept that two planes hit the towers. But those events are not sufficient to explain the dynamics of the collapse of WTC 1 or 2, and the issue of a plane is not a factor in the collapse of WTC 7.
As I have said--I am not trying to understand how the buildings were rigged (yet). I'm trying to understand how the official conspiricy theory could have happened as it relates to the buildings collapsing. If it turns out that there really is an explanation of the towers' collapse that is within the realm of the laws of physics and it can be proven that it was indeed why the buildings collapsed, then there will be no need to investigate the notion of a controlled demolition. You see, that's taking things one step at a time. That keeps you focused on a key issue and keeps you from getting caught up in unnecessary speculation. I'm looking for someone to show me how it is physically possible for the mass of the upper floors to collapse the rest of the structures that were Towers 1 & 2 without breaking any laws of physics. Then I want them to explain why Tower 7 fell in the same manner when there was no jet fuel to aid the process and no mass of upper floors. Interesting how the 9/11 commission report doesn't even mention building 7...
The steel in flooring is generally not just horizontal. It is fashioned like the joists of a wood floor to spread localized loads. While it might not be a big factor in the collapse, it would require energy to cause it to fail. But as I pointed out, Ross' analysis shows a collapse would not continue EVEN IGNORING the energy requirement of deforming the steel in the floor (which would have to occur for the floor to collapse). Are you familiar energy audits of scenarios like this? Are you familiar with the law of conservation of energy? Are you aware that a dynamic system such as the block of floors above the crash zone has a finite and determinable amount of kinetic energy and that the structure under the crash zone can absorb a finite and determinable amount of energy prior to material failure? An energy audit looks at the amount of energy going into the system versus the amount that can be absorbed by the system. If the amount of energy going into the system is less than or equal to the amount that can be absorbed prior to failure, there is no failure. If the amount going in is greater than the amount that can be absorbed prior to failure, then there is a failure. When Ross did the energy audit using Greenings own figures, and accounting for the propagation of the impact (which Greening fails to take into account), he comes up with an energy deficit--i.e., the kinetic energy of the block of floors above the crash zone, fueled by gravity alone is INSUFFICIENT to cause a sustained collapse. The first impacted floor, with the help of 24 floors that would have had energy propagated to them (although 16 floors would have been enough help) would not have failed. Now if the first impacted floor was dislocated from the floors below it--say by blowing out the major support structure--then it would be possible to achieve a sustained collapse.
Now weakening the support structure doesn't work to cause a sustained collapse, because the amount of kinetic energy needed to cause the collapse cannot be achieved due to the absorption of energy by the weakened steel. And have you ever heard of a heat sink? Do you have any idea how long a 1300 foot beam of steel would have to be subjected to 1100 degrees F before a local area would loose even 50% of its strength? And sensors recorded maximum temperatures of only 350 to 400 degrees. There are photos of people standing in the gashes made by the plane. If it was 1100 degrees in there, the people would be fried. Firefighers, also, reported only pockets of small fires on the floor that would have been the first impacted floor.
But oh, I forgot that our most wanted criminal commented on it all. But wait--he originally said he had nothing to do with it. Then, we saw video tapes that were obviously not bin Laden saying this and that, but we were told it was bin Laden. So nice of whoever it was to support the official story. And how odd that anyone who believed it was actually bin Laden (hey, maybe he is ambidexterous) would believe him to be telling the truth...! |
No witty quotes. I think for myself. |
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Dude
SFN Die Hard
USA
6891 Posts |
Posted - 10/01/2006 : 21:52:12 [Permalink]
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This administration can't keep secrets. Wiretapping, datamining, secret prisons, etc...
The controlled demolition of the twin towers would require a crew of HUNDREDS of people, working for many weeks, and making thousands of obvious alterations to the building. Then carrying in, literally, tons of explosives and (again, literally) miles of detonation wires.
But hey, you go on ahead and believe that all that could be done in secret (and kept secret) if it helps you sleep at night.
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Ignorance is preferable to error; and he is less remote from the truth who believes nothing, than he who believes what is wrong.
-- Thomas Jefferson
"god :: the last refuge of a man with no answers and no argument." - G. Carlin
Hope, n.
The handmaiden of desperation; the opiate of despair; the illegible signpost on the road to perdition. ~~ da filth |
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ergo123
BANNED
USA
810 Posts |
Posted - 10/01/2006 : 21:57:12 [Permalink]
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DaveW: I think you misread the paper. Ross' energy audit only shows a positive balance when one assumes each floor to be floating in mid air, with no support at all to overcome. That is the assumption Greening makes in his original analysis to which Ross is replying. But when the support of the lower floors is taken into account, the audit shows a negative balance. This negative balance is achieved EVEN WHEN IGNORING THE ENERGY NEEDED TO PULVERIZE THE CONCRETE AND ANY OTHER MATERIAL THAT GOT PULVERIZED. If these absorption factors were taken into account, the negative balance would have an even larger magnitude. DO you get how that works, logically? If A < B and C >= 0, then A < B + C. In other words, if you don't have enough money for a hamburger at the restaurant you are at, you won't have enough money for the prime rib either.
Neat calculations on the fall time. But you forgot to take into account that if materials are pulverized and ejected out beyond the footprint of the building, the mass of what IS above the footprint of the building becomes smaller in magnitude. In fact even the dust floating above the footprint cannot, by definition, be adding downward force to the system. I know pulverizing materials consumes energy. What I don't know is whether it takes time--or whether it is instantaneous. My guess is that it takes some amount of time to transfer the energy in the block of floors to the bonds that hold the materials together. And let's not forget that EVERYTHING (desks, chairs, copy machines, etc.) was pulverized. So if everything on say floor 50 is pulverized (along with everything above it) and shot out upwards (how does THAT happen) and sideways, how is it that there is enough mass to take out floor 49? And again, he uses 10% as a conservative number--favoring the system collapsing. Again--if he can show that if one only accounts for 10% of the known concrete being pulverized that no sustained collapse is possible, then it is also impossible to get a sustained collapse if one accounts for all of the concrete being pulverized.
Yeah--that's just it. Steel and concrete buildings don't pancake. Thanks for supporting my point.
Well, my first shot (I don't know if I'd consider it my best) seems to have confused you. I suggest you read it again. And remember, just because you don't understand it doesn't mean it's not correct. |
No witty quotes. I think for myself. |
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ergo123
BANNED
USA
810 Posts |
Posted - 10/01/2006 : 22:10:01 [Permalink]
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Dude: To assume the administration can't keep ANY secrets because it can't keep ALL their secrets is faulty logic.
So is assuming it was not a controlled demolition just because you can't figure out how it could be done. Our lack of understanding fusion didn't keep our sun from producing energy via fusion. And your assumptions about how long it would take to rig and how many people it would take to rig it are based on what? Remember, it did not have to be a perfect job (like it does when a building is brought down in a legit operation in a city). If you aren't concerned about losing lives when it comes down, a lot of time-intensive precautions can be skipped. And you can always overcome limits in explosive placement by adjusting the amount of explosives used.
But I will keep coming back to the physics--how is the official conspiricy theory possible? That's all I'm asking. |
No witty quotes. I think for myself. |
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wombatwal
New Member
Australia
20 Posts |
Posted - 10/01/2006 : 23:11:43 [Permalink]
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quote:
Originally posted by McQ
quote:
Originally posted by wombatwal
What is it with you Americans.
Every "big" event always has a conspiracy behind it.
President Kennedy's death.
Marilyn Monroe's death.
9/11.
Elvis Presley's death.
It goes on and on.
Why???
Gee, I didn't realize that people who believed in conspiracy theories had to be Americans. Thanks for pointing it out. 
At this very moment I'm in a debate with a Brit who thinks that the WTC, Flight 93, and Pentagon attacks occured just as ergo123 is suggesting.
I don't believe any of the above were government or other types of conspiracies. Except Elvis. And Marilyn Monroe. Maybe Kennedy. But that's all!
And Abraham Lincoln (oh wait, that sort of was a conspiracy).
Yes, point taken.
But the big conspiracy theories you hear about all come from the USA.
Moon landing conspiracy I also need to add. |
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H. Humbert
SFN Die Hard
USA
4574 Posts |
Posted - 10/01/2006 : 23:27:35 [Permalink]
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quote:
Originally posted by wombatwal
But the big conspiracy theories you hear about all come from the USA.
Eh, if you count religion as a type of conspiracy theory, I think the Middle East takes the cake.
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"A man is his own easiest dupe, for what he wishes to be true he generally believes to be true." --Demosthenes
"The first principle is that you must not fool yourself - and you are the easiest person to fool." --Richard P. Feynman
"Face facts with dignity." --found inside a fortune cookie |
| Edited by - H. Humbert on 10/01/2006 23:28:05 |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 10/02/2006 : 01:24:29 [Permalink]
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quote:
Originally posted by wombatwal
quote:
Originally posted by McQ
quote:
Originally posted by wombatwal
What is it with you Americans.
Every "big" event always has a conspiracy behind it.
President Kennedy's death.
Marilyn Monroe's death.
9/11.
Elvis Presley's death.
It goes on and on.
Why???
Gee, I didn't realize that people who believed in conspiracy theories had to be Americans. Thanks for pointing it out.
At this very moment I'm in a debate with a Brit who thinks that the WTC, Flight 93, and Pentagon attacks occured just as ergo123 is suggesting.
I don't believe any of the above were government or other types of conspiracies. Except Elvis. And Marilyn Monroe. Maybe Kennedy. But that's all!
And Abraham Lincoln (oh wait, that sort of was a conspiracy).
Yes, point taken.
But the big conspiracy theories you hear about all come from the USA.
Moon landing conspiracy I also need to add.
Yes we Yanks can be fair dinkum "creative" that way. But aside from the JFK assassination, I think only a minority of Americans actually believe these oddball theories. Some of them circulate more as trivial gossip than as held beliefs.
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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Cuneiformist
The Imperfectionist
USA
4955 Posts |
Posted - 10/02/2006 : 04:53:11 [Permalink]
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quote:
Originally posted by wombatwal
But the big conspiracy theories you hear about all come from the USA.
Moon landing conspiracy I also need to add.
Perhaps it's because all the events you listed actually involve the USA. |
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Valiant Dancer
Forum Goalie
USA
4826 Posts |
Posted - 10/02/2006 : 04:57:36 [Permalink]
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Why do I keep linking to sources when new conspiracy theorist posters just ignore the last ones?
The collapses were caused by the aircraft strikes coupled with the raging fire for WTC 1&2
http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html
WTC 7 had a raging diesel fuel fire due to a debris hit which touched off a diesel tank for emergency power. This fire was untreated because the fire suppression and rescue efforts were focused on WTC 1&2. WTC 7 was abandoned and left to burn. It collapsed due to the same types of stressors.
Your report ignores the effect of the weight of the floors above the collapse point. Fire + steel failure + gravity took the towers down. Explosives were not necessary. The building's construction contributed to the collapse because no one suspected someone would deliberately crash aircraft into buildings.
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Cthulhu/Asmodeus when you're tired of voting for the lesser of two evils
Brother Cutlass of Reasoned Discussion |
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ergo123
BANNED
USA
810 Posts |
Posted - 10/02/2006 : 09:32:40 [Permalink]
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Valiant Dancer: Maybe they ignore the articles you post links to because they have nothing to do with the topic at hand. In this oner, while you indicate the article references a raging fire, the article goes on at length that the fire was NOT a raging fire. At best, the article suggests that the fire weakened the supports holding up the floors above the crash zone. But if that was true, the floors above would not posess the kinetic energy required to cause the first impacted floor to fail (the article you posted does not address this issue at all).
In fact, it has been shown by Ross that even if it is assumed that all 287 support columns holding up the block of upper floors failed simultaneously and magically disappeared--so as to allow the upper block to freefall 3.7 meters into the first impacted floor--it would still not contain enough kinetic energy to cause the first impacted floor to fail.
So, whoever piloted the planes hit the towers too high for the floors above the crash zone to even cause a magical sustained let alone one that would surrender to the laws of physics. |
No witty quotes. I think for myself. |
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ergo123
BANNED
USA
810 Posts |
Posted - 10/02/2006 : 09:49:56 [Permalink]
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Also (for Valiant Dancer), the report I referenced did NOT ignore the weight of the floors above the crash zone. The whole point of the article was to show that the mass (that's "scientist talk" for weight) of the floors in the upper block above the crash zone did not posess enough kinetic energy, even if free-falling, to create a sustained collapse of the towers.
Further your comment about no one suspecting anyone would deliberately crash planes into the buildings is probably TECHNICALLY correct, but it is contrary to the fact that the building were designed to withstand several direct impacts from commercial airliners--although the designers probably figured it would happen by accident. But keep in mind that the dynamics of an accidental crash and a deliberate crash follow the same laws of physics.
And if WTC 7 fell due to fire, why have no other steel & concrete building ever before or since fell due to fire--even ones that burned much hotter for much longer? |
No witty quotes. I think for myself. |
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 10/02/2006 : 09:55:18 [Permalink]
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quote:
Originally posted by ergo123
DaveW: I think you misread the paper. Ross' energy audit only shows a positive balance when one assumes each floor to be floating in mid air, with no support at all to overcome. That is the assumption Greening makes in his original analysis to which Ross is replying. But when the support of the lower floors is taken into account, the audit shows a negative balance. This negative balance is achieved EVEN WHEN IGNORING THE ENERGY NEEDED TO PULVERIZE THE CONCRETE AND ANY OTHER MATERIAL THAT GOT PULVERIZED. If these absorption factors were taken into account, the negative balance would have an even larger magnitude.
You and Ross are again ignoring the fact that the upper storys wouldn't be starting with zero kinetic energy for such an analysis.quote:
DO you get how that works, logically? If A < B and C >= 0, then A < B + C. In other words, if you don't have enough money for a hamburger at the restaurant you are at, you won't have enough money for the prime rib either.
Nice condescending attitude you've got there, which when combined with the fact that the analysis requires that we forget about the coupon in our wallet, really makes you look the fool.quote:
Neat calculations on the fall time. But you forgot to take into account that if materials are pulverized and ejected out beyond the footprint of the building, the mass of what IS above the footprint of the building becomes smaller in magnitude.
According to Ross, it'd be 10% of the concrete in the impacting and impacted floors. I don't see how that figure is valid, but it doesn't matter since to follow the analysis, each floor below the top 15 would lose 20% of its mass. The total mass of the upper storys coming down still goes up as each floor is accelerated downward.quote:
In fact even the dust floating above the footprint cannot, by definition, be adding downward force to the system.
That's why nobody is claiming that it is.quote:
I know pulverizing materials consumes energy. What I don't know is whether it takes time--or whether it is instantaneous. My guess is that it takes some amount of time to transfer the energy in the block of floors to the bonds that hold the materials together.
Ross takes some time into account, but not all of it.quote:
And let's not forget that EVERYTHING (desks, chairs, copy machines, etc.) was pulverized.
And let's not forget that Ross failed to add the mass of the plane to his analysis, and also to remove the mass of all the burned materials (and also he failed to mention that the plane probably knocked a lot of concrete off of the beams that weren't severed by the crash).quote:
So if everything on say floor 50 is pulverized (along with everything above it) and shot out upwards (how does THAT happen) and sideways, how is it that there is enough mass to take out floor 49?
It's because you refuse to characterize your own references correctly: Ross figures only 10% of the concrete pulverized, not "everything." And how is it that you see anything being "shot out upwards" in the middle of a huge cloud of dust?quote:
And again, he uses 10% as a conservative number--favoring the system collapsing.
No, he used it because someone else used it - he doesn't offer any other reason for that number. Ross doesn't calculate it himself, nor does he discuss Greening's derivation of it.quote:
Again--if he can show that if one only accounts for 10% of the known concrete being pulverized that no sustained collapse is possible, then it is also impossible to get a sustained collapse if one accounts for all of the concrete being pulverized.
Ross doesn't even demonstrate that 10% of the concrete was pulverized.quote:
Yeah--that's just it. Steel and concrete buildings don't pancake. Thanks for supporting my point.
The only way I supported your point was if you ignore what I said and what's in Ross' analysis.quote:
Well, my first shot (I don't know if I'd consider it my best) seems to have confused you.
Only if you ignore what it says.quote:
I suggest you read it again.
Why don't you read it again, too?quote:
And remember, just because you don't understand it doesn't mean it's not correct.
And just because you think you understand it doesn't mean that it is correct. And I emphasize "think" there because while you said, "Neat calculations on the fall time," there were serious problems with my midnight calculations, like the fact that if the upper block is traveling at a speed above zero, then there simply isn't enough time for it to accelerate by 8.5 m/s with each floor. I didn't catch my own error until after I went to bed, but you didn't catch it at all, it seems.
Of course, I also didn't include the acceleration of a whole bunch of floors with each impact, as Ross does for his momentum calculation, but which Ross ignores for his strain calculations. Ross also neglects the pulverized concrete in his momentum calculations, assuming the mass of each floor before and after impact remains unchanged (instead of 17 floors of mass, there'd only be 16.8, increasing V2 from 4.772 m/s up to 4.806 m/s). But then, for Ross' oversimplified discussion of the momentum differences, the differential speed between the 17 upper floors (after the first impact) and the floor directly below would only be 0.2 m/s, so it would take over 18.5 seconds for them to meet, which is patently ridiculous. If the energy of the impact were to disperse into buckling the beams below, instead of accelerating 23 floors to insane velocities, that would make much more sense, but would also seriously change Ross' energy balance equations. Especially since with a difference in velocity of 0.2 m/s each, the columns would have had to have buckled after less than one second for all 24 of the next storys if Ross' momentum calculation were correct (because 0.2 m is larger than 0.167 m), and once the beams are buckled, the major energy loss is over, meaning the fall through the subsequent floors would have a very large energy surplus (by trying to add this in again after having already removed this energy in the form of momentum transfer is Ross' real major failing, accounting for the same energy loss twice). The momentum calculation also incorrectly assumes that each floor has the same mass, while we know that each floor - due to larger support beams, if nothing else - masses slightly more than the one above.
In short, Ross' analysis contains many shortcomings which you seem willing to overlook. |
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Dr. Mabuse
Septic Fiend
Sweden
9687 Posts |
Posted - 10/02/2006 : 10:18:13 [Permalink]
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quote:
Originally posted by ergo123
An energy audit looks at the amount of energy going into the system versus the amount that can be absorbed by the system. If the amount of energy going into the system is less than or equal to the amount that can be absorbed prior to failure, there is no failure.
Have a look on this scenario:
You drop an egg from 1m height.
This egg will have potential energy from 1m height converted to kinetic energy on impact.
If the impact zone is concrete, the the egg will break.
If the impact zone is grass-covered moss, the egg will hold.
What is the difference between the two?
It's the characteristic of the impulse.
When the egg hits the grass, the grass and moss is exerting force against the egg during a longer period of time, spreading out the energy over a longer period of time thus lowering the impulse force.
I haven't read the paper, so I cannot say... So I'm asking you, have the impulse force and impulse period of the collapse been taken into account? It all comes down to how flexible the concrete is. It is hard as stone, or more soft like moss?
Then we have elasticity. If the elasticity is high, then the collapsing floor will rebound, and not as much energy will go into waste energy of heat and pulverisation of concrete. (Have a peek how a Newton's Cradle works for high elasticity impacts) |
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The physics behind the collapses
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