Cannonfire is leaving

[erosoplier]

Thought these were funny:

[Iroquois]

erospolier,

Not to nitpick, but I don't believe that is the best analogy to explain Conservation of Momentum. What that rule says is that the velocity of the center of mass of an object will remain constant unless acted upon by an outside force.

This is, I believe, generally used in the argument for controlled demolition being used to bring down the three building of the World Trade Center to point out that the mass "picked up" by the previously falling structure has an initial velocity of 0, and when you add a bunch of mass with no velocity to an object with a given velocity, to maintain momentum, the velocity of the new total mass must decrease. Then, thanks to gravity, it starts accelerating again.

But, of course, the total collapse time in this process is much slower (I believe Infernal Optimist saying about this would result in a total collapse duration about twice that which was observed, which is itself about 1.5 times the official collapse duration) than for an object that free falls, continues accelerating through the whole descent, without picking up mass or meeting significant resistance, which I believe your analogy better depicts.

And, didn't "9/11: Press for Truth" mention something in the beginning about the peculiarity of the collapses? I would check myself, but I don't have the computer with the video saved on it with me at the moement.

[Infernal Optimist]

nomo:

Conservation of Momentum allows for the accumulation of energy from all those floors combined -- NOT the other way around.

You need to stop poo-pooing this until you at least understand it.

This is conservation of momentum:

m1v1 = m2v2

The product of the mass times the velocity stays the same. If your car hits a truck it will be moving more slowly afterwards than before. If a floor of a building hits another floor it will be moving more slowly afterwards than before.

Get it?

[Mad Onion]

Now this topic interests the Onion, who does not profess as much physics knowledge as others seem to have. Here is the official explanation regarding CD. Also included is the information on what resources were brought together to study this problem. The Onion is not decided on this question and finds much to be suspicious of regarding 9/11. Unfortunately, the Onion is also suspicious of those questioning 9/11. Onions, in fact, are suspicious by nature. At least the following will allow the debate to respond to what NIST actually said...

2. Why did NIST not consider a “controlled demolition” hypothesis with matching computer modeling and explanation as it did for the “pancake theory” hypothesis? A key critique of NIST’s work lies in the complete lack of analysis supporting a “progressive collapse” after the point of collapse initiation and the lack of consideration given to a controlled demolition hypothesis.

NIST conducted an extremely thorough three-year investigation into what caused the WTC towers to collapse, as explained in NIST’s dedicated Web site, http://wtc.nist.gov. This included consideration of a number of hypotheses for the collapses of the towers.

Some 200 technical experts—including about 85 career NIST experts and 125 leading experts from the private sector and academia—reviewed tens of thousands of documents, interviewed more than 1,000 people, reviewed 7,000 segments of video footage and 7,000 photographs, analyzed 236 pieces of steel from the wreckage, performed laboratory tests and sophisticated computer simulations of the sequence of events that occurred from the moment the aircraft struck the towers until they began to collapse.

Based on this comprehensive investigation, NIST concluded that the WTC towers collapsed because: (1) the impact of the planes severed and damaged support columns, dislodged fireproofing insulation coating the steel floor trusses and steel columns, and widely dispersed jet fuel over multiple floors; and (2) the subsequent unusually large jet-fuel ignited multi-floor fires (which reached temperatures as high as 1,000 degrees Celsius) significantly weakened the floors and columns with dislodged fireproofing to the point where floors sagged and pulled inward on the perimeter columns. This led to the inward bowing of the perimeter columns and failure of the south face of WTC 1 and the east face of WTC 2, initiating the collapse of each of the towers. Both photographic and video evidence—as well as accounts from the New York Police Department aviation unit during a half-hour period prior to collapse—support this sequence for each tower.

NIST’s findings do not support the “pancake theory” of collapse, which is premised on a progressive failure of the floor systems in the WTC towers (the composite floor system—that connected the core columns and the perimeter columns—consisted of a grid of steel “trusses” integrated with a concrete slab; see diagram below). Instead, the NIST investigation showed conclusively that the failure of the inwardly bowed perimeter columns initiated collapse and that the occurrence of this inward bowing required the sagging floors to remain connected to the columns and pull the columns inwards. Thus, the floors did not fail progressively to cause a pancaking phenomenon.
diagram of composit wtc floor system

Diagram of Composite WTC Floor System

NIST’s findings also do not support the “controlled demolition” theory since there is conclusive evidence that:

*

the collapse was initiated in the impact and fire floors of the WTC towers and nowhere else, and;

*

the time it took for the collapse to initiate (56 minutes for WTC 2 and 102 minutes for WTC 1) was dictated by (1) the extent of damage caused by the aircraft impact, and (2) the time it took for the fires to reach critical locations and weaken the structure to the point that the towers could not resist the tremendous energy released by the downward movement of the massive top section of the building at and above the fire and impact floors.

Video evidence also showed unambiguously that the collapse progressed from the top to the bottom, and there was no evidence (collected by NIST, or by the New York Police Department, the Port Authority Police Department or the Fire Department of New York) of any blast or explosions in the region below the impact and fire floors as the top building sections (including and above the 98th floor in WTC 1 and the 82nd floor in WTC 2) began their downward movement upon collapse initiation.

In summary, NIST found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to Sept. 11, 2001. NIST also did not find any evidence that missiles were fired at or hit the towers. Instead, photographs and videos from several angles clearly show that the collapse initiated at the fire and impact floors and that the collapse progressed from the initiating floors downward until the dust clouds obscured the view.

http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm

[Mad Onion]

Post Deleted.

Apologies for continued double posts. The Onion is trying to resolve the technical difficulties.

[erosoplier]

Iroquois, I think that the "10 metre diving platform/falling through sheets of water" example is an example of conservation of momentum (CoM) - it's just a very messy/impossible one to calculate. If a moving body runs into a stationary body in its path, its progress will be slowed - that's the basic upshot of the idea as it applies here. But the pure example of CoM is a small part of what actually went on with the WTC towers. You've got to put the the structural integrity of the building to one side - ie assume that each floor is somehow floating in mid air - and then imagine the falling top of the building running into each floor successively, and then you can see that pure conservation of momentum would slow the progress of the falling top significantly, solely due to CoM.

But there was so much stuff holding those floors up! To crush all those vertical steel beams down at the speed at which the tower came down - in the second case - I would guess that the small top section that initially started falling would have to have weighed at least 3 times the mass of the entire building. More like 6 times. It was like the finger of God was pushing down upon it.

[Mad Onion]

Two other relevant sections.

6. How could the WTC towers collapse in only 11 seconds (WTC 1) and 9 seconds (WTC 2)—speeds that approximate that of a ball dropped from similar height in a vacuum (with no air resistance)?

NIST estimated the elapsed times for the first exterior panels to strike the ground after the collapse initiated in each of the towers to be approximately 11 seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed times were based on: (1) precise timing of the initiation of collapse from video evidence, and (2) ground motion (seismic) signals recorded at Palisades, N.Y., that also were precisely time-calibrated for wave transmission times from lower Manhattan (see NCSTAR 1-5A).

As documented in Section 6.14.4 of NIST NCSTAR 1, these collapse times show that:

“… the structure below the level of collapse initiation offered minimal resistance to the falling building mass at and above the impact zone. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that energy through energy of deformation.

Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass.”

In other words, the momentum (which equals mass times velocity) of the 12 to 28 stories (WTC 1 and WTC 2, respectively) falling on the supporting structure below (which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum) so greatly exceeded the strength capacity of the structure below that it (the structure below) was unable to stop or even to slow the falling mass. The downward momentum felt by each successive lower floor was even larger due to the increasing mass.

From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse. Neither the duration of the seismic records nor video evidence (due to obstruction of view caused by debris clouds) are reliable indicators of the total time it took for each building to collapse completely.

7a. How could the steel have melted if the fires in the WTC towers weren’t hot enough to do so?
OR
7b. Since the melting point of steel is about 2,700 degrees Fahrenheit, the temperature of jet fuel fires does not exceed 1,800 degrees Fahrenheit and Underwriters Laboratories (UL) certified the steel in the WTC towers to 2,000 degrees Fahrenheit for six hours, how could fires have impacted the steel enough to bring down the WTC towers?

In no instance did NIST report that steel in the WTC towers melted due to the fires. The melting point of steel is about 1,500 degrees Celsius (2,800 degrees Fahrenheit). Normal building fires and hydrocarbon (e.g., jet fuel) fires generate temperatures up to about 1,100 degrees Celsius (2,000 degrees Fahrenheit). NIST reported maximum upper layer air temperatures of about 1,000 degrees Celsius (1,800 degrees Fahrenheit) in the WTC towers (for example, see NCSTAR 1, Figure 6-36).

However, when bare steel reaches temperatures of 1,000 degrees Celsius, it softens and its strength reduces to roughly 10 percent of its room temperature value. Steel that is unprotected (e.g., if the fireproofing is dislodged) can reach the air temperature within the time period that the fires burned within the towers. Thus, yielding and buckling of the steel members (floor trusses, beams, and both core and exterior columns) with missing fireproofing were expected under the fire intensity and duration determined by NIST for the WTC towers.

UL did not certify any steel as suggested. In fact, in U.S. practice, steel is not certified at all; rather structural assemblies are tested for their fire resistance rating in accordance with a standard procedure such as ASTM E 119 (see NCSTAR 1-6B). That the steel was “certified ... to 2000 degrees Fahrenheit for six hours” is simply not true.

The Onion notes with interest the omission of molten metal and hotspots in the second explanation. However, the Onion is also unaware of the pro-CD exlanation of how such hotspots persisted.

[orz]

If The Onion is going to keep talking in third person I suspect people are going to take The Onion's posts about as seriously as an article from The Onion.

falling on the supporting structure below (which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum)

This makes a lot of sense to me.

Since we all love tenuous demonstration analogies: if I arrange several empty cans and step onto them carefully they'd support my weight... however if I jump off a chair onto them, they'll crush easily.

[nomo]

nomo:

Conservation of Momentum allows for the accumulation of energy from all those floors combined -- NOT the other way around.

You need to stop poo-pooing this until you at least understand it.

This is conservation of momentum:

m1v1 = m2v2

The product of the mass times the velocity stays the same. If your car hits a truck it will be moving more slowly afterwards than before. If a floor of a building hits another floor it will be moving more slowly afterwards than before.

Get it?

What does this have to do with cars and trucks? Those ridiculous analogies (like the 10 meter diving platform mentioned above: huh???) make no sense. Can we at least focus on two of the largest building in the world?

We're talking about one floor falling on to another, and then those two floors falling on the third, and then those three falling on the fourth and so on. The added factor is gravity, and all those floors combined just have to keep falling faster and faster. Whatever resistance there was is negated by the constantly accumulating mass of floor after floor. Progressive collapse. What's so hard to understand?

[Infernal Optimist]

Nomo:

We're talking about one floor falling on to another, and then those two floors falling on the third, and then those three falling on the fourth and so on.

Yes, we are. Did you miss this:

If a floor of a building hits another floor it will be moving more slowly afterwards than before.

Nomo:

What's so hard to understand?

I have no idea. What's your problem?

[Mad Onion]

If The Onion is going to keep talking in third person I suspect people are going to take The Onion's posts about as seriously as an article from The Onion.

The poster clearly meant "third onion" and not "third person." The Onion forgives him for this unintentional slight. The Onion only speaks in first onion to those who've earned his trust. It is a dangerous and uncertain world.

As for the Onion website, it was founded by a second cousin of the Mad Onion, who is more properly understood as part of the Shallot bloodline. In fact, the Onion bloodline mixes with the Shallot line at many points which is a long story in itself.

The onion and its cousins — garlic, shallots, leeks, chives — are among the world's oldest cultivated plants and have a colorful history. With some exceptions — most notably the ancient Egyptians-onions were considered a coarse and inferior food by the upper classes. As a result, onions became a reliable staple for the poor for centuries, who often ate them raw on bread and washed it all down with beer. It wasn't until the 18th century that the lowly onion's reputation began to improve.

From Haynesworth's Return to Glory: A Brief History of the Onion Dynasty

The Shallot side of the family is represented in a far more flattering light in history and myth. Perhaps these immortal lines are familiar?

Yet who hath seen her wave her hand?
Or at the casement seen her stand?
Or is she know in all the land,
The Lady of Shalott?

[rrapt]

It is odd that this argument, at least half of which is supported by undocumented opinions of non-scientifically-educated posters, can go on so long.

Here is a nice neat synopsis of the collapse factors which have been mostly ingored. I am impressed by the thorough nature of it and the absence of opinion.

http://www.thetruthseeker.co.uk/article.asp?ID=5714

By a Danish physicist I believe. Suggested reading for nomo and orz at least.

[rocco33]

Why doesn't Hopsicker ponder on why the FBI didn't close down and confiscate Huffman Aviation when the 43 lbs. of H was found? He taunts us with this fact over and over again in his temper tantrums, but he rarely has given us any evidence to support his entertaining news reports. For example, it's very hard to believe that not one single journalist picked up the story that 5.5 tons of cocaine were found on a DHS/RNC linked commercial jet earlier this year and not one single media outlet in the whole world picked it up. Anyone else think this is odd?

[sunny]

I hate this thread became another fruitless CD debate. I say fruitless because what can be accomplished, really? Some will never believe in CD and some will never believe it didn't happen. Who will have the final say? Even if some well placed whistleblower were to come out and lay it all on the line, he or she will only be discredited or ignored. Just like the magic bullet theory- who really believes a single bullet caused 7 wounds in two men, yet this scurrilous theory is accepted as fact among the establishment, no matter how many times it is credibly refuted, 43 years on.

Do we expect the Bushies to hang their heads in embarrassment and admit they planted explosives?

Again, my purpose was to highlight the fact that Hoppy and Joe seem to be endorsing something similar to the official version, with the gov't covering up drug running through the Venice airport and little else- no prior knowledge, no actual complicity on the part of the admin. Is this really what they are saying? This is what I'm trying to discern and was hoping to get some discussion along these lines. Anyone care to parse this particular developement?

[nomo]

If a floor of a building hits another floor it will be moving more slowly afterwards than before.

Sigh. That would be true if you were talking about one floor falling onto one other floor. In this case, in case you weren't paying attention, we're talking about multiple floors falling onto eachother. 110 floors, in fact. Do you really believe that, say, the 30th floor is capable of slowing down the 80 floors above it?

If so, you must be on crack.