911 physics for dummies

[chris lz]

Perhaps this belongs in Sizzler’s recent thread. While there’s some overlap, I didn’t find exactly what I’m looking for (maybe I didn't look hard enough). Nor is my theme quite the same. Unlike Sizzler, I’ll state at the outset I’m not a truther by any stretch of the imagination (see Colboard.com) But for those with a pathetic physics background, I find in my debunking life I’m forced to rely on physics papers I can’t defend directly. So I'm curious, to what extent would the most basic physics claims supporting a “natural collapse” be accepted by all (or almost all) physicists? I'm confining myself to the twin towers for now. For instance, what formulas/calculations, etc., if shown to the average college level physics professor, would unhesitatingly be endorsed; and which ones (given by truthers) would be firmly rejected? Would they automatically reject Ross and Kuttler, in favor of Greening and Mackey, for example? Or might they be divided? The following are three all too common truther claims I'd like to look at in this regard:

1 As Prof. Jones likes to say, explosives were needed to “eliminate” or remove the mass to account for free fall/ almost free fall, every x floors.

2 -The twin towers fell into their own footprints (approximately, at least). And the related claim it took the path of “most resistance.” (comment: what would the path of most resistance actually be?)

3 -burning steel pieces (weighing thousands of pounds) of the towers were hurled outward for hundreds of feet at speeds of about one hundred feet per second. . . . . The other reason for ignoring the details of the collapses was that certain troubling aspects, [i.e. like the above observation], would not need to be analyzed.

The above quote is from EugeneAxeman, one of the more sophisticated 911 skeptic posters I’ve read on the internet. Here are a few more of his specific claims:



4-Calculations which took into account the energy consumption required to pulverize the buildings as observed show that the collapses took place at a rate over three times that which was possible by gravity alone.

(Where is he getting “over three times” from?)

5-In reality, steel bends, and over 200 supporting columns, along with their cross-bracing would need to get out of the way at once to allow the upper section to fall.

6-The physics I know tells me that when a building collapses, the energy is distributed across the surface area and the total mass of the falling section cannot be assumed to be focussed in a single point.

In fact, due to the inevitable fracturing and fragmenting suffered by the falling section, the collapse is better modelled as a series of interdependent impacts.

Kuttler simplified the model, but in the direction which would aid the gravity-driven presumption. Instead, it validated that the fall times were too fast, given the amount of material being destroyed by the collpase.


Less challenging, but still curious:

7-I have access to several videos of the tower collapses, and they all show a characteristically high volumes of smoke being expelled from the buildings just prior to their vertical movement. The smoke is consistent with the color of aluminum oxide generated from thermite reactions

8- The fires were not hot enough to weaken the steel to the point of failure, although efforts have been made to alter data and reality in order to meet that criteria

9-Even the NIST investigators had to distort the data to create their model where collapse inititiation would occur. Their own lab tests failed to duplicate the condition where the steel would sag to the degree to which they claim took place



So, for 1-6 at least, are we dealing primarily with questions of elementary physics? Or does one really need to go more in depth? What would be your one favorite formula/calculation/etc (if any) to quote when replying to any of these truther claims? (And, for any skeptics, what would be your favorite one that you think would refute the "natural collapse" physics?)

Thanks for helping the science-challenged, and for putting up with potentially already-answered-a-thousand-times-questions.

Chris

[beachnut]

All of it is BS. You should try looking up some of them and answer some of them yourself.

Jones made up his ideas 4 years after 9/11. Sad, because he missed the real work and investigation done. So his stuff you can throw out because it is nut case stuff. But of course calling his stuff nut case makes me wrong. But waking up 4 years after 9/11 and making up thermite is NUTS.

Number 2 is funny! Their own footprint. But look at your number 3. You would think someone in 9/11 truth would not debunk the other truthy stuff! See the big problem? Which is is 2, or 3. I choose 9/11, what happen on 9/11, not the made up junk of 9/11 truth.

Number 4, is a drug induces idiot statement. The building was not turned into dust! Idiots make up real sad stuff. Believe me #4 has to be a drug induced statement of woo. The idiots make it up to fool idiots. Funny how that works.

Number 5, as steel bends with it gets hot, it fails to hold the load. There are hundreds of examples of failed steel structures bent and failing killing many people under them. Just bend and stand is a fairy tale for idiots. (have not heard the cross bracing for a while)

Number 6, model it how you want, you will get the same result. Number 6 is more BS from idiots.

7 is from NUTS, there was no thermite planted in the WTC Jones made it up 4 years after 9/11. The smoke was normal for a building fire. 4 years! Jones was asleep for 4 years, he is nuts.

8 - fires were hot enough to make the WTC fail. Darn, I hate it when history debunks the idiots! This is hearsay made up BS. Check it out. Fires with much less fuel have destroyed steel structures.

9 - NIST did models to check what happen on 9/11; You need to look up the goals of NIST before you even touch this one; you need to at least read what NIST had to do and why some of there experiments were done the way they were done. 10,000 plus pages of NIST! But you can find the goals easy.

9/11 truth does not use physics, they make up lies. They can not even get the story straight, look at 2 and 3. It has been 6 years; why are the lies still being repeated.

How can you just find 9/11 truth JUNK, where are some fact based ideas?

[FramerDave]

The "path of most resistance" in this case happens to be down. Exactly the direction in which gravity works. Do we really need to make it any more complex than that?

The smoke is consistent with the color of aluminum oxide generated from thermite reactions

Ok, assume the color really is the same as that produced from a thermite reaction. Answer this: Is there any other reaction type or fuel source which might produce the same color smoke? Any at all?

[Sizzler]

What got me skeptical was this.

9.2 free fall in a vacuum.

~11 seconds with air resistance

~15 seconds with all the steel and building contents.

so.

air slowed it down by ~20%

where as all the steel slowed it down by ~40%

So when I look at those two ~percentages, I found (and to a lesser degree still find it) hard to imagine that all that steel only offered double the resistance of air.

However the engineers here have showed me that this is expected.

[beachnut]

What got me skeptical was this.

9.2 free fall in a vacuum.

~11 seconds with air resistance

~15 seconds with all the steel and building contents.

so.

air slowed it down by ~20%

where as all the steel slowed it down by ~40%

So when I look at those two ~percentages, I found (and to a lesser degree still find it) hard to imagine that all that steel only offered double the resistance of air.

However the engineers here have showed me that this is expected.
Where did you get 11 seconds with air? Show me the work now? Source?

[Sizzler]

Where did you get 11 seconds with air? Show me the work now? Source?

I asked the question in my thread.

~11 seconds was the answer.

Because you annoy me, go find it yourself.

[beachnut]

I asked the question in my thread.

~11 seconds was the answer.

Because you annoy me, go find it yourself.
:eek:

[chris lz]

All of it is BS. You should try looking up some of them and answer some of them yourself.

I certainly have. But it's rarely spelled out in such a way that a layman can understand easily. pp2-4 of the Benson Greening Bazant paper contain the most specific info I've seen on the basic collapse mechanism, but I still have trouble with it, not even knwoing much about many of the basic definitions you guys would.

How can you just find 9/11 truth JUNK, where are some fact based ideas?

I'm not understanding you. I only find Junk? I'm well aware of the science on both sides, as already indicated.

[chris lz]

The "path of most resistance" in this case happens to be down. Exactly the direction in which gravity works. Do we really need to make it any more complex than that?

So the path of most resistance and least resistance are both down?



Ok, assume the color really is the same as that produced from a thermite reaction. Answer this: Is there any other reaction type or fuel source which might produce the same color smoke? Any at all?

I posted that question not so much because of the color question, but because of the claim "high volume of smoke." In any case, I probably should have left it out, as it's not terribly specific.

[Gravy]

I asked the question in my thread.

~11 seconds was the answer.

Because you annoy me, go find it yourself.Did you also notice in that thread that 11 seconds was the approximate time from the roof of the building, not from the impact floors?

[Gravy]

So the path of most resistance and least resistance are both down?Yes, because it would take more energy to move that mass laterally so that it could fall through the air. Think of it as being the path of least energy change.

I posted that question not so much because of the color question, but because of the claim "high volume of smoke." In any case, I probably should have left it out, as it's not terribly specific.As with most of the statements you posted, the observation is simply wrong. There was no large volume of smoke expelled sideways before the collapses began, nor were there any detonations.

When dealing with truthers, before you go about investigating what caused an event they're questioning, you need to determine if that event happened at all.

[chris lz]

[COLOR=black]Number 2 is funny! Their own footprint. But look at your number 3. You would think someone in 9/11 truth would not debunk the other truthy stuff! See the big problem?




Of course I see what you mean. But that's why I used the word "approximately." The towers did -more or less - fall straight down. Now I assume that's a pretty easy physics question to explain. I'm not saying otherwise. But the question of rapid debris ejection is more interesting.

[beachnut]

I certainly have. But it's rarely spelled out in such a way that a layman can understand easily. pp2-4 of the Benson Greening Bazant paper contain the most specific info I've seen on the basic collapse mechanism, but I still have trouble with it, not even knwoing much about many of the basic definitions you guys would.

I'm not understanding you. I only find Junk? I'm well aware of the science on both sides, as already indicated.
You found only false information; how did you just get 9/11 truth junk? Are you on purpose looking for the lies?

The paper you found is good. Take it and your fall time questions to your local physics teacher, and ask them for some help to protect you from the fraud of 9/11 junk science. The teacher or professor can give you some ideas.

Of course you have only scratched the surface, there are thousands of junk ideas from 9/11 truth.

[Sizzler]

Did you also notice in that thread that 11 seconds was the approximate time from the roof of the building, not from the impact floors?

right.

But 9.2 is from the roof to the ground.

So you are right, but 9.2 would be less too.

Right?

[chris lz]

Everyone, if you think this thread is totally ridiculous, let me know and I'll delete it (if I can.) My main purpose is, to what extent are the main physics claims elementary questions, and to what extent is it going to be confirmed by any physics professor picked at random? I honestly, after over a year of reading this stuff, don't know 100% for sure. Sure, I'm pretty convinced. But I'm going after the "100% sure." When I read the Greening paper mentioned, I struggle with the definitions and formulas. Please appreciate how someone with hardly any science background might look at that stuff.

[Gravy]

right.
But 9.2 is from the roof to the ground.
So you are right, but 9.2 would be less too.
Right?Of course. As NIST points out, heavy items that did "free fall" from the collapse zones took about 9 seconds to hit the ground.

Sizzler, would you mind condensing your sentences? Your posts take up a lot of screen space for a few words.

[Sizzler]

Everyone, if you think this thread is totally ridiculous, let me know and I'll delete it (if I can.) My main purpose is, to what extent are the main physics claims elementary questions, and to what extent is it going to be confirmed by any physics professor picked at random? I honestly, after over a year of reading this stuff, don't know 100% for sure. Sure, I'm pretty convinced. But I'm going after the "100% sure." When I read the Greening paper mentioned, I struggle with the definitions and formulas. Please appreciate how someone with hardly any science background might look at that stuff.

Don't delete it.

I am more or less in the same position as you.

This is a good post for people working through all the claims, but don't have expertise.

[Sizzler]

Of course. As NIST points out, heavy items that did "free fall" from the collapse zones took about 9 seconds to hit the ground.

why did you use " " for free fall.

[Hokulele]

I certainly have. But it's rarely spelled out in such a way that a layman can understand easily. pp2-4 of the Benson Greening Bazant paper contain the most specific info I've seen on the basic collapse mechanism, but I still have trouble with it, not even knwoing much about many of the basic definitions you guys would.


One of the challenges with physics is that there are many situations that are not easily spelled out in such a way that a layman can understand them easily. Much of physics really is counter-intuitive unless you can do/have done the math (which is why some physicists can get a little testy when questioned). Here is a classic example of counter-intuitive physics.

http://www.physics.umd.edu/lecdem/services/demos/demosf3/f3-02.htm

There was a whole thread of these things posted here some time ago. I may try to go dig it up.

ETA: Found it.

http://forums.randi.org/showthread.php?postid=2226771#post2226771

[beachnut]

Of course I see what you mean. But that's why I used the word "approximately." The towers did -more or less - fall straight down. Now I assume that's a pretty easy physics question to explain. I'm not saying otherwise. But the question of rapid debris ejection is more interesting.
The 2 acres of towers spread junk over 19 acres. Saying their own footprint is not exactly correct, it depends on which truther is telling you what. Some say too much was ejected due to bombs, some say it fell straight down like a CD. 2 and 3 are funny. The towers fell down like they did, in chaos, but just like expected; (so says the expert who built them).

He would be the best source, the guy who built them.

http://www.physicsclassroom.com/ some basic stuff to help understand if you have time

[chris lz]

You found only false information; how did you just get 9/11 truth junk? Are you on purpose looking for the lies?

Beachnut, I don't quite understand why you keep saying I've only found 9/11 truth junk. Look at my first post! I mention papers by Greening and Mackey. I read the whole Mackey paper. I've read the recent critique of Jones in Gravy's links. You seem to have missed the point of my post.

The paper you found is good. Take it and your fall time questions to your local physics teacher, and ask them for some help to protect you from the fraud of 9/11 junk science. The teacher or professor can give you some ideas.

That's precisely why I posted this here !!!! Because this is supposed to be a good place to get help with understanding the physics.


Beachnut, I don't understand where you're coming from. Look, if your tired with truthers, fine. But don't take your frustrations out on me. I"M NOT A TRUTHER, and I'm aware of all the important physics papers from debunkers. It was in my very first post !!! I just don't understand them as well as you do. Right now, I'm getting the "hitting a brick wall" feeling when I argue with truthers. Honestly, why are you intent on putting a negative spin on what I write? I consider myself part of the debunker mvt.

[LashL]

Oh, look. Here we go again. :rolleyes:

[Sizzler]

Oh, look. Here we go again. :rolleyes:

Oh my god........

Are people seriously asking questions again????

Oh the humanity.

Grow up.

[Reality Believer]

STOP!

Just stop for a minute or ten and ask yourself why a big exploration of physics is even necessary.

The towers fell, this is a fact that is in not dispute by anyone. They are gone.

You either believe that it was caused by aircraft impact and fire, or not.

If not, then endeavor to explain why not. This is the real question, yes?

Why is this issue becoming so complicated?

[Sizzler]

Sizzler, would you mind condensing your sentences? Your posts take up a lot of screen space for a few words.

point taken.

[Gravy]

Everyone, if you think this thread is totally ridiculous, let me know and I'll delete it (if I can.) My main purpose is, to what extent are the main physics claims elementary questions, and to what extent is it going to be confirmed by any physics professor picked at random? I honestly, after over a year of reading this stuff, don't know 100% for sure. Sure, I'm pretty convinced. But I'm going after the "100% sure." When I read the Greening paper mentioned, I struggle with the definitions and formulas. Please appreciate how someone with hardly any science background might look at that stuff.It all depends on the question. For instance, the first question requires knowledge of the structure in order to calculate its resistance. The second question is one of elementary physics. The third is based on a false premise.

Why are you only "pretty convinced" that the 9/11 skyscrapers collapsed from damage and fire? Does it give you pause that the 9/11 deniers haven't produced a single paper about the engineering or physics of the collapses that would pass muster in a reputable journal?

[Sizzler]

STOP!

Just stop for a minute or ten and ask yourself why a big exploration of physics is even necessary.

The towers fell, this is a fact that is in not dispute by anyone. They are gone.

You either believe that it was caused by aircraft impact and fire, or not.

If not, then endeavor to explain why not. This is the real question, yes?

Why is this issue becoming so complicated?

Some people are on the fence. I am one of them. So what should I do in my case?

[chris lz]

STOP!

Just stop for a minute or ten and ask yourself why a big exploration of physics is even necessary.

The towers fell, this is a fact that is in not dispute by anyone. They are gone.

You either believe that it was caused by aircraft impact and fire, or not.

If not, then endeavor to explain why not. This is the real question, yes?

Why is this issue becoming so complicated?

OK, well then why don't you ask Mackey and Greening why they waste their time with their physics papers? If they're going to write them, and people here recommend them, then what on earth is wrong with asking for some help in trying to understanding them better?

[Gravy]

Some people are on the fence. I am one of them. So what should I do in my case?Get informed. Don't rely on people who get nothing right for your information, as you had been doing. Is this really difficult to understand?

[Sizzler]

It all depends on the question. For instance, the first question requires knowledge of the structure in order to calculate its resistance. The second question is one of elementary physics. The third is based on a false premise.

Why are you only "pretty convinced" that the 9/11 skyscrapers collapsed from damage and fire? Does it give you pause that the 9/11 deniers haven't produced a single paper about the engineering or physics of the collapses that would pass muster in a reputable journal?

Would a reputable journal even consider publishing a solid, fact based paper that refutes 9-11? I don't think it is possible given the current climate.

[gumboot]

1 As Prof. Jones likes to say, explosives were needed to “eliminate” or remove the mass to account for free fall/ almost free fall, every x floors.

Collapse speed was neither freefall nor "almost" free fall.


2 -The twin towers fell into their own footprints (approximately, at least). And the related claim it took the path of “most resistance.” (comment: what would the path of most resistance actually be?)

The towers did not fall into their own footprint, nor even remotely close to their own footprint. They did not topple over, however, as this would require enormous lateral force that cannot be explained.


3 - burning steel pieces (weighing thousands of pounds) of the towers were hurled outward for hundreds of feet at speeds of about one hundred feet per second. . . . .

Objects falling due to gravity attain a speed of 100feet per second in the space of three seconds.

The observation of material landing hundreds of feet from the towers directly refutes the previous claim. Material landed so far away because the exterior column network peeled away from the towers in enormous multi-floor sections. This sections pivoted around the bottom point (as one would expect) resulting in significant lateral forces being applied to the stop sections, throwing them outwards as the column structure broke up (think of it like swinging your arm forwards holding a ball while outstretched, and imagine then letting go of the ball, will it fall straight down, or outwards?).




Calculations which took into account the energy consumption required to pulverize the buildings as observed show that the collapses took place at a rate over three times that which was possible by gravity alone.

The towers did not collapse in 3 seconds, so this is total garbage. The buildings were also not pulverized.




In reality, steel bends, and over 200 supporting columns, along with their cross-bracing would need to get out of the way at once to allow the upper section to fall.

The exterior columns peeled outwards ahead of the collapse wave, and the upper section twisted out of alignment with the core columns - the major collapse force was applied to the floor trusses which were never intended to hold any significant loading.


I have access to several videos of the tower collapses, and they all show a characteristically high volumes of smoke being expelled from the buildings just prior to their vertical movement. The smoke is consistent with the color of aluminum oxide generated from thermite reactions

The high volumes of smoke were on account of the buildings being on fire. The smoke was black, as expected from the burning of carbon-rich fuel. Thermite reactions produce white smoke.



The fires were not hot enough to weaken the steel to the point of failure, although efforts have been made to alter data and reality in order to meet that criteria

The fires in the WTC reached temperatures of 1000 degrees centigrade. At this temperature steel loses 90% of its load bearing capacity.



Even the NIST investigators had to distort the data to create their model where collapse inititiation would occur. Their own lab tests failed to duplicate the condition where the steel would sag to the degree to which they claim took place

It is standard scientific practise to "tweak" models so that they accurately reflect the reality of what happened. You do not tweak reality to more accurately reflect the model.

The lab tests on floor truss sagging were not designed to imitate conditions in the WTC, but to establish fire performance benchmarks for the assembly in question.

-Gumboot

[beachnut]

Beachnut, I don't quite understand why you keep saying I've only found 9/11 truth junk. Look at my first post! I mention papers by Greening and Mackey. I read the whole Mackey paper. I've read the recent critique of Jones in Gravy's links. You seem to have missed the point of my post.



That's precisely why I posted this here !!!! Because this is supposed to be a good place to get help with understanding the physics.


Beachnut, I don't understand where you're coming from. Look, if your tired with truthers, fine. But don't take your frustrations out on me. I"M NOT A TRUTHER, and I'm aware of all the important physics papers from debunkers. It was in my very first post !!! I just don't understand them as well as you do. Right now, I'm getting the "hitting a brick wall" feeling when I argue with truthers. Honestly, why are you intent on putting a negative spin on what I write? I consider myself part of the debunker mvt.
I said you found just 9/11 truth junk, I was asking how you did it and did not find one real conclusion based in facts.

You need to focus and keep going. I was amazed you collected just truther junk, that is an observation, so?

Yep you have mentioned other work, but you did not seem to learn anything as you said. So? You can carry on, or can you? Either get busy with what you want or get upset, 9/11 is an event, 9/11 truth is a cult.

[Gravy]

Would a reputable journal even consider publishing a solid, fact based paper that refutes 9-11? I don't think it is possible given the current climate.You'll have to wait until such a paper is produced, mmkay? :rolleyes:

[Reality Believer]

OK, well then why don't you ask Mackey and Greening why they waste their time with their physics papers? If they're going to write them, and people here recommend them, then what on earth is wrong with asking for some help in trying to understanding them better?
My question stands. If you doubt the impact and fire scenario, then explain the alternative with equal completeness and credulity of the recognized authorities.

[beachnut]

OK, well then why don't you ask Mackey and Greening why they waste their time with their physics papers? If they're going to write them, and people here recommend them, then what on earth is wrong with asking for some help in trying to understanding them better?
They do the papers since liars who say they are experts mislead the people unable to understand. The 9/11 truth movement is based on false information.

[Hokulele]

Right. Now that this is starting to devolve into name-calling, and the posts with links actually relevant to the topic (mine and beachnut's second try) are rapidly being left behind, I am going to try again starting with the OP.

... So I'm curious, to what extent would the most basic physics claims supporting a “natural collapse” be accepted by all (or almost all) physicists? I'm confining myself to the twin towers for now. For instance, what formulas/calculations, etc., if shown to the average college level physics professor, would unhesitatingly be endorsed; and which ones (given by truthers) would be firmly rejected? Would they automatically reject Ross and Kuttler, in favor of Greening and Mackey, for example? Or might they be divided?...


One strong indication that the papers by Bazant and Greening (leaving Mackey out of this for now) would be much more strongly accepted than Ross and Kuttler is the simple fact that Bazant, Greening, et al have been accepted by people with the appropriate background. Just look at which papers were peer-reviewed and published in the journals endorsed by the reputable trade and industry groups and which ones have not. This strongly suggests which side is supported by people with a background in the relevant fields.

Thanks for helping the science-challenged, and for putting up with potentially already-answered-a-thousand-times-questions.

Chris


And this statement pretty much describes why you are facing the hostility in this thread. I know the search engine on this forum sucks dead bears (unless you are particularly Google-enlightened), but the information really is there.

I would recommend backing up, asking one specific question, allowing people to either post a single reply or links containing previously posted replies, rather than splurging out all 9 questions in one go. :)

[beachnut]

Would a reputable journal even consider publishing a solid, fact based paper that refutes 9-11? I don't think it is possible given the current climate.
There are not facts to support the thermite junk and CD. What do you mean refutes 9/11? Which part exactly?

Added; Gravy is right; this is best doing it yourself and look up your questions first, then ask questions. You can start by building yourself some information you can back with real sources.

[Corsair 115]

Would a reputable journal even consider publishing a solid, fact based paper that refutes 9-11? I don't think it is possible given the current climate.Are you saying that you think politics plays a role in determining whether a deserving paper gets published in a scientific journal? What about scientific journals published outside the United States? How would they be subject to American politics?

[Gravy]

The towers did not collapse in 3 seconds, so this is total garbage. The buildings were also not pulverized.I think the claim there is that the gravity collapses should have taken longer without the building's supports being removed by explosives or somesuch.

The exterior columns peeled outwards ahead of the collapse wave.I disagree with that statement. I think it's clear that the exterior columns peeled away as, and after, the collapse wave hit them.

[Sizzler]

Get informed. Don't rely on people who get nothing right for your information, as you had been doing. Is this really difficult to understand?

You say so. Others say you have it wrong. Who can I trust? So I need to weigh all information for myself.

[Sizzler]

Are you saying that you think politics plays a role in determining whether a deserving paper gets published in a scientific journal? What about scientific journals published outside the United States? How would they be subject to American politics?

Of course politics play into controversial science. Look at the global warming debate. Trans-fat debate. Etc.

American politics is global politics.

[chris lz]

It all depends on the question. For instance, the first question requires knowledge of the structure in order to calculate its resistance. The second question is one of elementary physics. The third is based on a false premise.

Why are you only "pretty convinced" that the 9/11 skyscrapers collapsed from damage and fire? Does it give you pause that the 9/11 deniers haven't produced a single paper about the engineering or physics of the collapses that would pass muster in a reputable journal?

Hi again Gravy.

Sorry, my fault, but there's been a slight misunderstanding. I don't mean to imply I'm only "pretty convinced" the towers weren't imploded. I've never for a moment seriously doubted that 9/11 truth "science" is pure nonsense. What I meant by "pretty sure" is the idea that the basic physics arguments in support of the "natural collapse" are uncontroversial among even basic college level physics professors. Why? Because, not being a science-trained person, I am not sure how complex the physics is, such that all it takes are a few uncontroversial laws or formulas that any physics teacher could immediately see. Hope you see my narrower point!

I guess my main area of interest is about free fall speed. Is it as easy as what's stated on pp2-4 of the Greening Bazant paper? If so, I'll post some of it and ask for help in interpreting it, because it's not easy for me. I fully admit to being a total science ignoramus.

Cheers

[Sizzler]

You'll have to wait until such a paper is produced, mmkay? :rolleyes:

Yes of course.

[Reality Believer]

Guys, it isn't this hard. Lets skip ahead. Suppose you have concluded in your mind that impact / fire is not the cause. What next? What is the next question?

[chris lz]

I said you found just 9/11 truth junk, I was asking how you did it and did not find one real conclusion based in facts.

You need to focus and keep going. I was amazed you collected just truther junk, that is an observation, so?

Yep you have mentioned other work, but you did not seem to learn anything as you said. So? You can carry on, or can you? Either get busy with what you want or get upset, 9/11 is an event, 9/11 truth is a cult.

I never questioned the truth of Greening's work and so on. My primary questions were: how much of the physics needed to refute the truthers is basic and elementary; and (therefore) would there be a unanimous consensus among even physics professors who aren't specialists in anything. Nothing I've said in anyway shape of form has been an endorsement of the validity of the truth mvt. Sizzler, I'm not in the same position of you. I'm not on any fence. I just desire help in intepreting the science so I don't have to say all the time to truthers "read paper X."


OK, enough complaining. I'll try to be much more specific in my future questions on this thread. I guess I'm surprised that on a forum which I have respect for, one that I consider a great friend, especially in 911 debunking matters, that I would be greeted with this kind of - dare I say - cold reception.

Look, if this forum isn't supposed to be for non-science types to ask questions, let me know and I'll stop posting here !

[LashL]

Oh my god........

Are people seriously asking questions again????

Oh the humanity.

Grow up.


Ahem, "Sizzler": Are your posts always as stupid as the one above or was that just an anomaly for you? Frankly, it appears that the former is far more likely than the latter.

[Sizzler]

Guys, it isn't this hard. Lets skip ahead. Suppose you have concluded in your mind that impact / fire is not the cause. What next? What is the next question?

Next question is, what made them fall?

[Sizzler]

Are your posts always as stupid as the one above or was that just an anomaly for you? Frankly, it appears that the former is far more likely than the latter.

:boggled:

[Reality Believer]

Next question is, what made them fall?
Please explore that then because the audience here is comfortable with impact \ fire.

[gumboot]

I think the claim there is that the gravity collapses should have taken longer without the building's supports being removed by explosives or somesuch.

Ah yes, I see now.


I disagree with that statement. I think it's clear that the exterior columns peeled away as, and after, the collapse wave hit them.


The collapse wave reaches floor 50, and the exterior columns are pushed outwards at floor 50 by the debris, however rather than just the section at floor 50 peeling out, a 20 floor section of the exterior column grid begins to peel away - extending from floor 50 to floor 30. The exterior columns are now peeling away 20 floors ahead of the collapse wave.

-Gumboot

[Sizzler]

Please explore that then because the audience here is comfortable with impact \ fire.

Considering I haven't ruled out fire/impact, I will remain. If and when I rule it out, I will move on.

[chris lz]

First, let us review the basic argument (Baˇzant 2001; Baˇzant and Zhou 2002). After a drop
through at least the height h of one story heated by fire (stage 3 in Fig. 1 top), the mass
m of the upper part of each tower has lost enormous gravitational energy, equal to mgh (g
= gravity acceleration). Because the energy dissipation by buckling of the hot columns must
have been negligible by comparison, most of this energy must have been converted into kinetic
energy K = mv2/2 of the upper part of tower, moving at velocity v. Calculation of energy Wc
dissipated by the crushing of all columns of the underlying (cold and intact) story (Baˇzant and
Zhou 2002) showed that, approximately, the kinetic energy of impact K > 8.4 Wc.
In calculating Wc, it was noted that, in inelastic buckling, the inelastic deformation must
localize into inelastic hinges (Baˇzant and Cedolin 2003, sec. 7.10)). To obtain an upper bound
on Wc, the local buckling of flanges and webs, as well as possible steel fracture, was neglected
(which means that the ratio K/Wc was likely higher than 8.4). When the subsequent stories
are getting crushed, the loss mgh of gravitational energy per story exceeds Wc that by an ever
increasing margin, and so the velocity v of the upper part must increase from one story to the
next. This is the basic characteristic of progressive collapse, well known from many previous
disasters with causes other than fire (internal or external explosions, earthquake, lapses in
quality control; see, e.g., Levy and Salvadori 1992; Baˇzant and Verdure 2007).
Merely to get convinced of the inevitability of gravity driven progressive collapse, further
analysis is, for a structural engineer, superfluous.

That's from p. 2 of the Greening Bazant paper.

Specific question: is that all the physics one needs in order to show the possibility of global collapse ?

Specific question: If I went and handed this excerpt to my local physics professor, would he accept it as basic, uncontroversial proof of this?

Are these silly, worthless question?

[LashL]

:boggled:


I can only take that as an admission on your part that, yes, your post was stupid (which it clearly was), and I have no reason to think that your subsequent posts were any less stupid unless and until you provide evidence to the contrary (which you have failed to do to date).

[Gravy]

That's from p. 2 of the Greening Bazant paper.

Specific question: is that all the physics one needs in order to show the possibility of global collapse ?

Specific question: If I went and handed this excerpt to my local physics professor, would he accept it as basic, uncontroversial proof of this? Your physics professor would need to be versed in structural engineering to be able to pass judgment on Bazant's papers. However, that professor would easily be able to understand #1 and #10 in NIST's latest FAQ (http://wtc.nist.gov/pubs/factsheets/faqs_12_2007.htm). Still, to declare the calculations correct, he'd need to verify that the masses and strengths of connections are correctly stated by NIST.

[Gravy]

Next question is, what made them fall?Please refer to your existing thread about that topic.

[uk_dave]

Of course politics play into controversial science. Look at the global warming debate. Trans-fat debate. Etc.

American politics is global politics.

Are you saying that the scientific community would only publish papers on global warming which complied with the Bush admins stance?

I'd be interested to see proof of this given that for many years the Bush admin denied climate change was happening, then agreed that it was happening but that it was nothing to do with us, and only recently have they accepted the tenets of AGW. And yet during this time scientific publications were on the whole taking a very different stance to that of the US Government.

You think professionals and academics would shy away from supporting an engineering paper which supported the CD hypothesis if it was credible?

[beachnut]

That's from p. 2 of the Greening Bazant paper.

Specific question: is that all the physics one needs in order to show the possibility of global collapse ?

Specific question: If I went and handed this excerpt to my local physics professor, would he accept it as basic, uncontroversial proof of this?

Are these silly, worthless question?
Those are great questions, and I would go to a physics professor if he will take the time.

[chris lz]

Those are great questions, and I would go to a physics professor if he will take the time.

I very much have been planning to do that. The reason I came here first is to try and narrow down the specific arguments/calculations to be evaluated. I don't want to walk in to some professor's office, throw a bunch of science papers at him and say, "read." A scientific ignoramous I may be. But a truther, or one who only collects junk I'm not. Please don't confuse me with Sizzler. I'm just trying to get a feel for how much one has to know to be the master of 9/11 physics. I'm as passionately against "9/11 truth" as you or Gravy. Sorry if I somehow conveyed otherwise.

Thanks

[chris lz]

And this statement pretty much describes why you are facing the hostility in this thread. I know the search engine on this forum sucks dead bears (unless you are particularly Google-enlightened), but the information really is there.


OK, all I'm really saying is, I've been reading about 9/11 truth and reading the debunking claims for years now. What I'm seeking is not new information, but a more layman-oriented distillation of the papers I've been mentioning. The stuff i read is either very technical on the one hand, or too watered down on the other. Anyone can say "the experts say." And science writers are very good at going above the heads of the science-challenged. I think it would be hugely helpful for the debunkers like me to have at their disposal something a little more solid and irrefutable than "no peer review paper exists," but not so technical that I have to go running to a physics professor to understand and accept that the collapse model is something anyone can come to understand, and based on completely uncontroversial physics. If you'll notice, such papers written with that nice blend of very detailed physics, and yet distilled for a lay audience unfamiliar with most of the principles being utilized, are far and few. At least I haven't found one yet.

[Sizzler]

Are you saying that the scientific community would only publish papers on global warming which complied with the Bush admins stance?

I'd be interested to see proof of this given that for many years the Bush admin denied climate change was happening, then agreed that it was happening but that it was nothing to do with us, and only recently have they accepted the tenets of AGW. And yet during this time scientific publications were on the whole taking a very different stance to that of the US Government.

You think professionals and academics would shy away from supporting an engineering paper which supported the CD hypothesis if it was credible?

You make a good point with the global warming.

Before I can answer your question. Can you answer this one:

Who owns various engineering journals? (I don't know)

[Sizzler]

Your physics professor would need to be versed in structural engineering to be able to pass judgment on Bazant's papers. However, that professor would easily be able to understand #1 and #10 in NIST's latest FAQ (http://wtc.nist.gov/pubs/factsheets/faqs_12_2007.htm). Still, to declare the calculations correct, he'd need to verify that the masses and strengths of connections are correctly stated by NIST.

How do we know the calculations are correct?

[uk_dave]

Who owns various engineering journals? (I don't know)

I don't know either. Google is your friend.

But if an engineering journal doesn't publish letters and articles by engineers simply because those letters and articles may go against the publishers ideology, then there's obviously going to be a market for a new journal which doesn't have such constraints.

Or all the engineers just tow the line too? Ever spoken with one?

Perhaps you might consider the issue of professional indemnity insurance which all structural engineers have to carry, as well as the requirement for professional engineers to engage in what in the UK is known as Continuing Professional Development (CPD) in order for them to maintain their membership of their professional bodies. Engineers have to satisfy both their insurers and their professional bodies that they are up to date and know what they're talking about. I suspect in that climate they are unlikely to subscribe to a technical journal which does not supply them with information which impacts upon their professional knowledge.

[chris lz]

Who owns various engineering journals? (I don't know)



Sizzler,

Not my forum, but there's already another thread questioning the collapse physics. I had hoped this wouldn't become another 500-post repeat of that. Any chance you could take the discussion over there? I didn't start this thread to question the basic validity of the "natural collapse" science, or global warming, etc.

Thanks

[Sizzler]

Sizzler,

Not my forum, but there's already another thread questioning the collapse physics. I had hoped this wouldn't become another 500-post repeat of that. Any chance you could take the discussion over there? I didn't start this thread to question the basic validity of the "natural collapse" science, or global warming, etc.

Thanks

sure. movin along.

[leftysergeant]

Not all of the answers even require a knowledge of physics.

As a fire fighter, cook, construction laborer and model buildier, I observed phenomena and handled materials which give me an insight into things that the ivory-tower-dwellers like Jones miss.

Like the resemblance between Jones' "thermite chips" and ordinary paint chips.

Like the resemblance between the "white puffs of smoke" immediately following the start of collapse and crushed wall board.

Like the abscence of the blinding white light which would have to have attended the burning of thermite.

As for the time of the collapse, there are two ways that we can help you straighten that out in your mind.

I first figured that to be BS by watching videos and examining stills of the collapse of the north tower. There are visible pieces of solid matter falling more than half the distance to the ground from the zone of collapse. Since the unattached objects cannot be falling faster than free-fall, and the zone of collapse is falling behind in relation to the free objects, the collapse is occurring at far less than free-fall speed.

RKOwens4, who posts to this forum has posted some very good video on YouTube to explain away many of these points.

Mark Roberts, posting as Gravy, has prepared a very informative 45 minute video on the collapses of the buildings to specificly address some of the issues. I highly recommend that you watch it. I find it useful when twoofers ask me to back up a claim that seems to them counter-intuitive.

Is that helpful at all?

[funk de fino]

Of course politics play into controversial science. Look at the global warming debate. Trans-fat debate. Etc.

American politics is global politics.

that is a crock and lame

[Dave Rogers]

Chris,

Maybe the opinion of a physicist might be of interest here - not a professor, but a chartered physicist with over 20 years' experience, so I'm probably as near as you'll get on the forum.

The collapses of the WTC towers involve a lot of concepts that aren't exactly everyday stuff for physicists; yield strengths of steel girders, failure modes, fire progression modelling are a few examples. In fact I get the impression that it's not even exactly mainstream stuff for structural engineers, who are generally far better placed to follow the details of the analysis than we are. In order to understand what's going on in the discussions, I've had to learn a lot, and people like Newtons Bit and Gregory Urich know all this a lot better than I do. From that alone, I suspect therefore that if you put all the papers on the WTC collapses on a physics professor's desk and asked him whether they proved that the collapses were to be expected, the most likely answer would be "Let me get back to you on that." There's still a debate here on whether Bazant's work proves the inevitability of global collapse given collapse initiation, and there are valid arguments on both sides (although, given that the model is so simplified, even this is far from casting any doubt on the likelihood of global collapse in the real world), so overall it's far from trivial or obvious.

Looking at the other side of the debate, things may get a bit simpler. There are some physicists who have written papers claiming that the towers couldn't have collapsed, and I've posted some criticisms of those papers here. In general they have some glaring errors or invalid assumptions that lie at the heart of their argument, and I'd expect a reasonably alert physics professor to pick up on those errors. However, in some cases it can be tricky to see exactly where the error lies, because of a bad habit the truth movement seems to have picked up. This is the habit of taking inadequate evidence that something has occurred and assuming it to be reliable, and in some cases assuming that it proves an even more extreme case even than the evidence suggests. For example, Kenneth Kuttler starts from an anonymous report that some rescue workers found no concrete particles larger than dust in the section of the WTC debris pile they were searching, and from this derives the assumption that (1) all the concrete in the WTC towers was pulverised into fine dust, (2) this happened to all the concrete in a given floor in the first impact of that floor on another, and (3) all this dust was immediately ejected from the tower and hence could not contribute to the collapse. This sort of nonsense can be difficult for a physicist to spot, because we tend to believe that papers like this are written with good faith and common sense. It's sometimes more an area for general skepticism and examination of claims - more in common with investigative journalism than physics.

Once we start to understand the issues and actually do some calculations, the physics-based arguments of the truth movement are like snowflakes in July, because in general they rely on stating that it is intuitively obvious that an unevaluated quantity is equal to, or unequal to, some other unevaluated quantity, and arguments like that cannot stand up when the quantities are actually evaluated and examined. However, sometimes it takes more than the experience of a physicist to know how to do the maths.

In summary, the physics of fire and damage initiated collapse is generally correct but not trivial. The physics of the truth movement is generally erroneous, and the physics of those errors is generally trivial, but the derivation often is not.

Dave

[chris lz]

Not all of the answers even require a knowledge of physics.



Thanks. Watched the video just yesterday in fact. As always, great stuff from him. While I do appreciate your taking the time to reply, again, I'm not seriously doubting "the basic answers." Never was the intended purpose of this post. That seems to be entirely my fault for writing a poorly worded post and putting in too many trivial questions.

I fully and completely accept that 9/11 happened the way the mainstream says. Maybe the moderators might want to just delete this thread all together, as it's back-firing more than I would ever have expected.

[chris lz]

sorry duplicate

[T.A.M.]

All Engineering Journals are owned by a big bad Corporation. This corporation, like all the others control the entire world, including government. As a result, ONLY articles that are in compliance with the NWO protocols and policies are allowed to be published. The "Peer Review" is just a sham, and is always overridden by the desires of the NWO, as put forth by the "upper guys" within the Corp...so say the lord...

TAM;);)

[westprog]

Of course I see what you mean. But that's why I used the word "approximately." The towers did -more or less - fall straight down. Now I assume that's a pretty easy physics question to explain. I'm not saying otherwise. But the question of rapid debris ejection is more interesting.

It seems surprising until you think about what was happening during the collapse. As the structure failed, pieces of steel were subject to enormous forces. Steel is good at absorbing such force without shattering or bending. When enough energy is absorbed, the steel might break loose. The energy would then be released. This would be amply sufficient to hurl the steel long distances. Imagine a flexible steel rod being held vertically on a concrete floor. Keep pushing down on the rod. What's going to happen?

Once I've visualised the situation, I don't feel the need for the detailed physics.

[westprog]

Would a reputable journal even consider publishing a solid, fact based paper that refutes 9-11? I don't think it is possible given the current climate.

Suppose that the Western world had the situation sewn up, and had everyone blackmailed into silence. That still leaves the entire rest of the world. There are engineers in Russia, India, Japan and even Iran who could refute the consensus without consequence. They'd even get a bit of a bonus for exposing the USA. George W Bush doesn't rule the world.

Even though the Islamic world has a vast level of belief in the conspiracy theories, no reputable Muslim engineer or scientist has attempted, in a scientific journal, to show that the towers could not fall due to aircraft impact and fire.

[chris lz]

Chris,

Maybe the opinion of a physicist might be of interest here - not a professor, but a chartered physicist with over 20 years' experience, so I'm probably as near as you'll get on the forum.

The collapses of the WTC towers involve a lot of concepts that aren't exactly everyday stuff for physicists; yield strengths of steel girders, failure modes, fire progression modelling are a few examples. In fact I get the impression that it's not even exactly mainstream stuff for structural engineers, who are generally far better placed to follow the details of the analysis than we are. In order to understand what's going on in the discussions, I've had to learn a lot, . . . so overall it's far from trivial or obvious

What a great post. For me, I don't feel a need to know the collapses were "inevitable." I'm content merely to know from a physics/math perspective why they were possible, and why the times observed are possible without the aide of explosives. So am I correct in interpreting your post as saying there's no one simple equation or law or formula one can just throw at a truther and say, "there, end of discussion"?

[Dave Rogers]

What a great post. For me, I don't feel a need to know the collapses were "inevitable." I'm content merely to know from a physics/math perspective why they were possible, and why the times observed are possible without the aide of explosives. So am I correct in interpreting your post as saying there's no one simple equation or law or formula one can just throw at a truther and say, "there, end of discussion"?

Exactly, or we would have already done it. There are just a whole raft of perfectly sensible arguments about why the collapses were energetically favourable and physically reasonable ranged against a series of logical fallacies.

Mind you, there are times when there is a simple equation, law or formula one can throw at a truther and say "there, end of discussion". The normal result is that they go away for a few days then come back saying the same thing all over again as if it never happened.

Dave

[CHF]

Only twoofers find it odd that a 50,000 ton mass falls straight down (ie in the direction of gravity).

Where was it supposed to go, kids? Straight up? Off to the side perhaps?

[Apollo20]

Chris lz:

One catch phrase used a lot by "truthers" is: "X defies the laws of physics". Where X is some phenomenon such as near free fall collapse.

The fact is that NOTHING defies the laws of physics (except in STAR-TREK movies!).

So next time a truther tells you that, tell him that he is simply incorrect. The laws of physics applied to the collapse of WTC 1 & 2 all the way from start to finish.

However, it is important to remember that these universal laws also apply to a CD which is mostly a gravity-driven collapse anyway! So the truthers have to have their physics straight too............

But rememeber, physics can only tell you what is possible and what is not possible.

What I found surprising once I got into my calculations was that a lot of things that look "impossible" about the collapse of WTC 1 & 2 turn out to be quite possible. That is why calculations are important. Without them you are relying on intuition and intuition is frequently wrong! For example, it is NOT intuitively obvious that objects of different mass should fall at the same rate... but experiment shows that they do!

[rwguinn]

What got me skeptical was this.

9.2 free fall in a vacuum.

~11 seconds with air resistance

~15 seconds with all the steel and building contents.

so.

air slowed it down by ~20%

where as all the steel slowed it down by ~40%

So when I look at those two ~percentages, I found (and to a lesser degree still find it) hard to imagine that all that steel only offered double the resistance of air.

However the engineers here have showed me that this is expected.

I asked the question in my thread.

~11 seconds was the answer.

Because you annoy me, go find it yourself.

Did you also notice in that thread that 11 seconds was the approximate time from the roof of the building, not from the impact floors?

right.

But 9.2 is from the roof to the ground.

So you are right, but 9.2 would be less too.

Right?

Your twoofiness is showing.
You can do the calculations. I gave you the damn equation, back on page 1 of your exposure thread.
If 11s is from the top of the building, as you agree, how can 9.2s also be from the top of the building?
I saw nothing about air resistance in any answers--and the ballistic coefficient for the chunks of steel is such that in the distance they had to fall, air resistance is neglegible.
You, sir, are a liar and a fraud.

[Anti-sophist]

Hey Chris. Here's my response to these issues ...


1 As Prof. Jones likes to say, explosives were needed to “eliminate” or remove the mass to account for free fall/ almost free fall, every x floors.
Bazant, Greening and others have shown this is just plain false. Any truther who makes this claim simply needs to be asked to demonstrate it. If they appeal to Jones' authority, you appeal to Bazant/Greening/etc.

Most truthers will -claim- the building couldn't have fallen in N seconds, but they will unable to provide even the simplest explanation why.


2 -The twin towers fell into their own footprints (approximately, at least). And the related claim it took the path of “most resistance.” (comment: what would the path of most resistance actually be?)
The notion that objects travel the path of least resistance is an emergent property of certain physical systems based on simpler laws of physics. It's not a law of physics.

Buildings aren't electrons. They don't follow the path of least resistance. They follow Newton's laws. The notion that there is a path of "least resistance" and that is somehow physically or scientifically relevant is fallacious.


burning steel pieces (weighing thousands of pounds) of the towers were hurled outward for hundreds of feet at speeds of about one hundred feet per second. . I don't see how this is inconsistent with a gravity driven collapse.




Calculations which took into account the energy consumption required to pulverize the buildings as observed show that the collapses took place at a rate over three times that which was possible by gravity alone.

(Where is he getting “over three times” from?)He's basically appealing to someone elses flawed calculation that the building fell too fast given the amount of energy required to create all the dust we saw. The flaw in the truther calculation is that the estimation of the quantity and finest of the dust is beyond absurd.

There are several such calculations that truthers have pushed and all have been dealt with in gory detail on this forum somewhere or another.


In reality, steel bends, and over 200 supporting columns, along with their cross-bracing would need to get out of the way at once to allow the upper section to fall
This is just nonsense appeal to intuition that is classic Eugene. The reality of the issue is that at impacts at 500mph and catastrophic building collapses produce physical phenomena we aren't familiar with and our inherent intuition is consequently flawed.



I have access to several videos of the tower collapses, and they all show a characteristically high volumes of smoke being expelled from the buildings just prior to their vertical movement. The smoke is consistent with the color of aluminum oxide generated from thermite reactions

Affirming the consequent fallacy. It's also consistent with the smoke generated from magical pixies with laser beams shooting out of their eyes. Doesn't make it true.

The fires were not hot enough to weaken the steel to the point of failure, although efforts have been made to alter data and reality in order to meet that criteria
Have you gotten him to show you proof of this altered data? God knows I've tried.

[Minadin]

Chris lz:

One catch phrase used a lot by "truthers" is: "X defies the laws of physics". Where X is some phenomenon such as near free fall collapse.

The fact is that NOTHING defies the laws of physics (except in STAR-TREK movies!).

So next time a truther tells you that, tell him that he is simply incorrect. The laws of physics applied to the collapse of WTC 1 & 2 all the way from start to finish.

However, it is important to remember that these universal laws also apply to a CD which is mostly a gravity-driven collapse anyway! So the truthers have to have their physics straight too............

But rememeber, physics can only tell you what is possible and what is not possible.

What I found surprising once I got into my calculations was that a lot of things that look "impossible" about the collapse of WTC 1 & 2 turn out to be quite possible. That is why calculations are important. Without them you are relying on intuition and intuition is frequently wrong! For example, it is NOT intuitively obvious that objects of different mass should fall at the same rate... but experiment shows that they do!

I've often made the same point as what I've bolded in Apollo20's quote above. An idea, a notion, your own imagination - these things can "violate the laws of physics". Reality cannot. If something even appears to be happening outside of our understanding of the laws of physics, it is our understanding which is at fault and not the laws or the event.

But, I wanted to quote the whole post because it all bears repeating and was very well and succinctly put.

[Anti-sophist]

I've often made the same point as what I've bolded in Apollo20's quote above. An idea, a notion, your own imagination - these things can "violate the laws of physics". Reality cannot. If something even appears to be happening outside of our understanding of the laws of physics, it is our understanding which is at fault and not the laws or the event.

But, I wanted to quote the whole post because it all bears repeating and was very well and succinctly put.

I think this is a somewhat pedantic argument. Truthers aren't claiming that the buildings actually violated the laws of physics. They are trying to form a proof by contradiction. They are saying that if the official story of the collapse was correct, then it violated the known laws of physics, therefore the official story can't be correct.

[lozenge124]

chris lz,

Usually to get a handle on complex real-world problems and treat them mathematically certain simplifying assumptions have to be made. So while the math in papers like Bazant Verdure may be too complex for most people to follow, the assumptions made prior to the development of equations are often understandable to the layman.

For example, here are the assumptions from the Bazant Verdure paper for their "Crush down, crush-up" model. The equations developed based on these assumptions were also used in the Bazant Greening Benson paper.

One-Dimensional Continuum Model for Crushing Front Propagation:

Detailed finite element analysis simulating plasticity and break-ups of all column and beams, and the flight and collisions of broken pieces, would be extremely difficult, as well as unsuited for extracting the basic general trends. Thus it appears reasonable to make four simplifying hypotheses:
(i) The only displacements are vertical and only the mean of vertical displacement over the whole floor needs to be considered.
(ii) Energy is dissipated only at the crushing front (this implies that the blocks in Fig.2 may be treated rigid,i.e., deformations of the blocks away from the crushing front may be neglected).
(iii)The relation of resisting normal force F transmitted by columns of each floor to the relative displacement u between two adjacent floors obeys a known load-displacement diagram (Fig.4,terminating with a specified compaction ratio (which must be adjusted to take into account lateral shedding of a certain known fraction of rubble outside the tower perimeter)).
(iv)The stories are so numerous, and the collapse front traverses so many stories, that a continuum smearing(i.e.,homogenization)gives a sufficiently accurate overall picture.

The value of any model is only as good as the assumptions it is based upon, and I think anyone can read the assumptions here and formulate an opinion on its validity, even without fully understanding the math treatment that follows.

[Belz...]

Of course I see what you mean. But that's why I used the word "approximately." The towers did -more or less - fall straight down.

Exactly how would you expect gravity to do its thing ?

[Alferd_Packer]

From the OP

burning steel pieces (weighing thousands of pounds) of the towers were hurled outward for hundreds of feet at speeds of about one hundred feet per second.

“burning steel pieces?” Wow, that’s almost worth a stundie nomination. And how did he determine ” speeds of about one hundred feet per second?”


In reality, steel bends, and over 200 supporting columns, along with their cross-bracing would need to get out of the way at once to allow the upper section to fall.

Yes, steel bends. Learn and understand the concept of “plastic hinge failure” as it applies to structural systems.

”. . .along with their cross-bracing. . . “ What exactly are we talking about here? The term “cross bracing” generally refers to diagonal bracing. There was limited use of “cross bracing” in the tower structure. Are you referring to the spandrel plate, the hat truss, the floor trusses, the core beams?

Finally, consider the inherent Failure to comprehendin the following statement:

“steel bends, and over 200 supporting columns, along with their cross-bracing would need to get out of the way at once”

Yes “getting out of the way” is what happens when something bends. Sudden, catastrophic onset is a hallmark of a buckling ( http://mysite.du.edu/~jcalvert/tech/machines/buckling.htm ) (i.e. bending) type failure. Since the inward bowing of the exterior columns was noted several minutes before the collapse began, how can you say “at once?”


The physics I know tells me that when a building collapses, the energy is distributed across the surface area and the total mass of the falling section cannot be assumed to be focussed in a single point.

Wow, I haven’t seen anyone compare the hollow towers to a solid in a long while. Who here remembers the old “it should have fallen over like a tree” argument?



The smoke is consistent with the color of aluminum oxide generated from thermite reactions

Or it could be the color of the drywall (white), ceiling tiles (white), and fireproofing (off white/ grey) from the building materials?


The fires were not hot enough to weaken the steel to the point of failure,

I’d like to see what justification he comes up with to support this statement. Even a bunk bed fire in a bedroom can generate temperatures hot enough to weaken steel to the point of failure.


although efforts have been made (by truthers) to alter data and reality in order to (deny that fire can weaken steel)

There, I fixed that for you.



Even the NIST investigators had to distort the data to create their model where collapse inititiation would occur. Their own lab tests failed to duplicate the condition where the steel would sag to the degree to which they claim took place


OK, repeat after me: “Intact” - “Dislodged” say each word clearly and carefully.

UL tests were of the “as designed” floor assemblies with intact fireproofing. The NIST collapse initiation scenario was based on the premise that the impacts “dislodged” the existing fireproofing (Which by the way, was almost certainly not the same and deficient to what was specified.)

[Jonnyclueless]

Ah...dummies for 9/11 physics.

[nicepants]

I think this is a somewhat pedantic argument. Truthers aren't claiming that the buildings actually violated the laws of physics. They are trying to form a proof by contradiction. They are saying that if the official story of the collapse was correct, then it violated the known laws of physics, therefore the official story can't be correct.

I've heard Dylan say this many times. Of course, none of the twoofers seem to be able to successfully explain HOW the OT violates the laws of physics. I love when they try, though...it just shows how little they know about the subject.

[Alferd_Packer]

On the other hand, I've seen the claim that the buildings actually fell faster than free fall.

[uk_dave]

On the other hand, I've seen the claim that the buildings actually fell faster than free fall.

Ahhh but that was coz the gound woz rising due to the rotashun of teh earth.

[nicepants]

On the other hand, I've seen the claim that the buildings actually fell faster than free fall.

That's right up there with the claim that Newton's Third Law was violated. Something about equal and opposite damage.

[leftysergeant]

Excuse me. Where does anmyone find "burning" pieces of steel. I saw no burning steel. I saw steel with entrained dust behind it, but not burning steel. This is based, possibly on some idiot's claim that there was buring thermite attached to the steel. There has never been a single piece of steel recovered with thermite residues on it, nor was there any blindingly bright light recorded in the falling rubble.

[Corsair 115]

Of course politics play into controversial science. Look at the global warming debate. Trans-fat debate. Etc.

American politics is global politics.Perhaps you've missed how anti-Americanism is on the rise in many countries over the last number of years. So if anything there'd be a greater chance of studies being published.

Where are they?

Seriously, if you're relying on politics to explain why no studies have been published, you're on an extremely thin branch of the tree. You're going to have to come up with something more substantial than that. Your position is little better than that of the CTist who rails against the mainstream media for not carrying stories about the many supposedly suspicious things about 9/11 who conveniently ignore how the media in all the nations outside the United States could possibly be controlled by the U.S. government.

[Brainache]

Speaking as someone who's science background is dimly remembered high school biology, I'd like to echo the posters who have said "what's to question?".

Either the towers fell as a result of the damamge caused by the plane impacts and the fires, or they didn't. Quibbling over "Crush Up/Crush Down","KE","Dynamic Loads V Static Loads" etc is just that: Quibbling.

Anyone who denies the planes + fire caused the collapse needs to present a case at least as plausible which explains what we saw more fully than the "Official Story". Until they do there really is nothing meaningful to discuss.

I don't understand the math involved in Bazant's or Greening's work, but I know what I saw on TV that day and on video since.

I know about politics and paranoia in a general kind of way. I have always been one to question what people in authority tell me and all I can say is: Nothing I have seen in the 6+ years since 9/11 has pointed towards anything like the kind of Sci-Fi scenarios dreamed up by Truthers. Their fantasies are laughable, their ignorance astonishing and their lies are transparent.

As always, just one bloke's opinion.

[R.Mackey]

I thought I'd lend my perspective, albeit perhaps too late. I hope the contentious nature of this thread hasn't totally scared away chris lz already. The questions aren't new, but they're asked in good faith, so why not give reasonable answers?

So I'm curious, to what extent would the most basic physics claims supporting a “natural collapse” be accepted by all (or almost all) physicists? I'm confining myself to the twin towers for now. For instance, what formulas/calculations, etc., if shown to the average college level physics professor, would unhesitatingly be endorsed; and which ones (given by truthers) would be firmly rejected? Would they automatically reject Ross and Kuttler, in favor of Greening and Mackey, for example? Or might they be divided?

It's hard to say what all physics professors would say, but in general, I'm comfortable that the Truth Movement claims would be rejected out of hand. You are welcome to test this yourself with your local college. It's entirely possible you will find an oddball prof here or there who buys into it (the Truth Movement has found a handful, and throw their names around as though they were worth a million Ameros each), but I would be stunned indeed if an entire department agreed, anywhere in the world.

I say this for several reasons:
The structural engineering faculty at BYU, former home of Steven Jones, completely disagreed (http://newsnet.byu.edu/story.cfm/57724) with his conclusions, while pointedly making no move to censor him
Several university efforts have looked into Sept. 11th, including top-of-the-line schools MIT and Purdue, and agree with no conspiracy theories
As you've already seen, there is a multitude of published work from legitimate sciences about the physics of Sept. 11th, and while not all of it agrees with NIST, none of it agrees with the conspiracists
So that's my evidence. Again, it's an experiment you can test for yourself, and you should if you have such serious doubts.


1 As Prof. Jones likes to say, explosives were needed to “eliminate” or remove the mass to account for free fall/ almost free fall, every x floors.
Dr. Jones must be very careful about what "almost free-fall" means. As I've explained before, collapses are rapid. Only a second or two of resistance translates into an enormous amount of energy expended on the structure, much more than any feasible explosives situation could provide. See post here (http://forums.randi.org/showthread.php?postid=2236462#post2236462) or Appendix A of my whitepaper.


2 -The twin towers fell into their own footprints (approximately, at least). And the related claim it took the path of “most resistance.” (comment: what would the path of most resistance actually be?)

Falling vertically actually is the path of least resistance. Getting the structures to topple, or shedding mass over the sides such that collapse was arrested, requires energy to move all that mass sideways. Where could it have come from?

The Towers were so enormous -- both in mass, and in width, that there's just no way. Even if you imagine the upper block rotating as it falls, it still has to crush tens of floors on one side just to rotate, say, 45 degrees. You cannot have tipping without crushing. Crushing without (much) tipping requires less energy than crushing and tipping.


The above quote is from EugeneAxeman, one of the more sophisticated 911 skeptic posters I’ve read on the internet. Here are a few more of his specific claims:burning steel pieces (weighing thousands of pounds) of the towers were hurled outward for hundreds of feet at speeds of about one hundred feet per second. . . . . The other reason for ignoring the details of the collapses was that certain troubling aspects, [i.e. like the above observation], would not need to be analyzed.


We've seen Mr. Axeman here, too. He did not strike me as particularly well educated in matters of science.

His observation is actually evidence against explosives. As he notes, the pieces seen to have flown the furthest were very large. (I dispute his estimate of "hundreds of feet per second;" the fastest velocity supported by evidence is on the order of 50 feet per second.) This makes sense, because larger pieces are less affected by wind resistance, right?

Well, the problem is that pieces being accelerated by blast is also much like "wind resistance." The bigger pieces aren't accelerated as much as smaller pieces. Had explosives been to blame, we would see smaller pieces fly farther than the bigger pieces. Unless you expect me to believe that a blast big enough to toss those girders couldn't have broken off anything else. Such a surgical yet huge explosive is simply not possible.

In this post (http://forums.randi.org/showthread.php?postid=2835665#post2835665) (and in my whitepaper) I explained this, and later on in that thread I work out the amount of explosives needed to throw large chunks of steel. The amount works out to be a minimum of perhaps 500 kg of TNT, just to throw a modest steel column segment 600 kg in mass the distance claimed, under optimistic assumptions. Such as, that doesn't include the energy to break it loose in the first place -- just to throw it.

Unless you can believe there were half-ton charges of demo going off without being heard or seen by anyone, there's no way you can accept this as evidence of explosives.


Calculations which took into account the energy consumption required to pulverize the buildings as observed show that the collapses took place at a rate over three times that which was possible by gravity alone.

(Where is he getting “over three times” from?)
I have no idea. Like explained above, the collapse time is totally believable, even if you can't hack through the BLBG paper. Even a high-school level argument explains why the ~ 15 second collapse times are reasonable.


In reality, steel bends, and over 200 supporting columns, along with their cross-bracing would need to get out of the way at once to allow the upper section to fall.


The "at once" argument is laughable on its face. Did the columns "all fail at once" when the aircraft hit? Nope. Some did, most didn't. Did the columns "all fail at once" when the top of the building began leaning? Nope.

At the critical moment of loss of stability, however, many columns can fail in a fraction of a second. Think of it this way: Suppose you have a sturdy table with eight legs, and you put an enormous amount of weight on it, enough that it starts to creak and sag. Then kick out one of the legs. The table will probably stay standing, but it will complain. Kick out another leg. Eventually, when you kick out a leg, the rest will all collapse, and it will happen faster than you can see. But that doesn't mean they all failed at once. It's just what happens when there's no more reserve capacity in a highly energetic system.


The physics I know tells me that when a building collapses, the energy is distributed across the surface area and the total mass of the falling section cannot be assumed to be focussed in a single point.

In fact, due to the inevitable fracturing and fragmenting suffered by the falling section, the collapse is better modelled as a series of interdependent impacts.

Kuttler simplified the model, but in the direction which would aid the gravity-driven presumption. Instead, it validated that the fall times were too fast, given the amount of material being destroyed by the collpase.


Poster Dave Rogers has already adequately addressed (http://forums.randi.org/showthread.php?t=98714) the Kuttler paper. There are numerous totally bizarre assumptions, none of them backed by observation or physics, that leads to his incorrect answer, such as the claim that 100% of the concrete was pulverized at altitude rather than later -- even Steven Jones points out that much concrete survived, as a way to shut up the Beam Weapon loonies. He also arbitrarily assumes the structure should continually and gradually resist the collapse, much like a giant sponge, rather than fail floor-by-floor in sharp and discrete impact events. All in all, a rather stupid paper.


I have access to several videos of the tower collapses, and they all show a characteristically high volumes of smoke being expelled from the buildings just prior to their vertical movement. The smoke is consistent with the color of aluminum oxide generated from thermite reactions


The Towers were full of smoke, and at the moment of collapse initiation, the NIST theory predicts several floor systems giving way. It's no surprise at all that "high volumes of smoke" would be expelled. The smoke is the color of the smoke. Aluminum oxide powder is roughly the same color as wallboard, so this is hardly a compelling argument.

The fires were not hot enough to weaken the steel to the point of failure, although efforts have been made to alter data and reality in order to meet that criteria

This comment is nonsensical. The "point of failure" depends on the load. Steel can fail at room temperature, if you load it enough. NIST explains in gruesome detail the temperatures and the loads it predicts, as a function of time, and these do indeed lead to failure.

Even the NIST investigators had to distort the data to create their model where collapse inititiation would occur. Their own lab tests failed to duplicate the condition where the steel would sag to the degree to which they claim took place

This is simply wrong. Mr. Axeman, like so many of his fellows in the Truth Movement, has misunderstood the point of the ASTM E119 tests in NCSTAR1-6B. They were designed to see if the intact floor trusses would pass their fire certification. They bear no direct relationship to trusses with damaged fireproofing or structural damage from impact, and the test results are not comparable. You may as well argue that your car can go 140 MPH, because that's what Road & Track said, even though your car has a flat tire.


So, for 1-6 at least, are we dealing primarily with questions of elementary physics? Or does one really need to go more in depth? What would be your one favorite formula/calculation/etc (if any) to quote when replying to any of these truther claims? (And, for any skeptics, what would be your favorite one that you think would refute the "natural collapse" physics?)


For questions 1-5, it only takes a modicum of physics understanding. Any competent Physics major should be able to find the errors and explain them at a coarse level. Question 6 is trickier simply because of the deliberately confusing nature of Kuttler's paper.

Reports like the NIST Report can be read and understood with, say, an undergraduate level of physics or engineering -- although it is rather dense and detailed. Actually disputing it would be difficult without post-graduate training, but there are researchers (real ones) who do exactly that, e.g. Dr. Usmani at U of Edinburgh or Dr. Quintiere at U Maryland. But all of these folks strongly disagree with any conspiracy angle. They're merely looking at issues of precision, special vulnerabilities of the structural design, etc. Not postulating explosives.

As is common for the Truth Movement, few of the questions above are well-posed, and several depend on Truth Movement lore that will throw an unprepared reader for a loop, without prior exposure to their ideas. This is all typical behavior for pseudoscientific groups, who are extremely fond of inventing terms and fixating on details that most people may have never heard of. It lends them an undeserved air of thoroughness and legitimacy, and makes it harder for people to challenge them. But if one takes the time to look closely, they're still wrong.

Hope that helps.

[leftysergeant]

The Towers were full of smoke, and at the moment of collapse initiation, the NIST theory predicts several floor systems giving way. It's no surprise at all that "high volumes of smoke" would be expelled. The smoke is the color of the smoke. Aluminum oxide powder is roughly the same color as wallboard, so this is hardly a compelling argument.


Thank you for bringing that back up. Here, one need not even be an engineer, if one has a little real-world experience with materials suspected or known to have been present in the towers.

I have experience with both thermite (as a military fire fighter trained in arson investigations) and wall board (as a day laborer in all manner of jobs.)

Note in any video that there is black smoke pouring out the tops of the impact area even as collapse begins. No gfreat quantity of white smoke beyond what one should expect from a small amount of burning paper until the first falling floors make contact with the first stationary floors in their path.

The first time I set off a thermite charge, a cast thermite in an 8 ounce styrofoam cup, it produced a fountain of sparks that left an after-image on my eyes for the rest of the day (bloody cheap sun glasses!) Sparks blew roughly 50 feet into the air and dense white and VERY HOT smoke rose even farther. Hot gases, even with unusually heavy particals entrained with it, will rise, inevitably.

But when the first puffs of white dust or smoke appear at the collapse zone, they begin falling as quickly as even some of the solid debris.

I shouldn't think this white dust or smoke could have been very warm.

In support of his Bad Science, Jones even offers up a small thermite discharge. It is apparently less bright than mine was, and of a slightly different composition, but you can see for yourself that it is so bright as to be hard to conceal even against a clear sunny sky. You will also note that the smoke rises rather energeticly.

Thus, the white puffs behave more as one would expect pulverised sheetrock to behave.

How much energy would that take? Don't ask me. I'm utterly discalculic.

But in five minutes of pounding and whacking at the walls of a twenty by twenty-foot kitchen, another gentleman and I produced an adequate amount of very fine powder that we had to dash outside to replace our dust masks because we could no longer breathe through them.

I shouldn't think the energy budget to produce even the volumns escaping from the towers was particularly great.

[chris lz]

I hope the contentious nature of this thread hasn't totally scared away chris lz already.

No, not at all. I sense among some here a knee-jerk reaction that any questions regarding 9/11 science are automatically assumed to be unreasonable or disguised attempts a truther- mischief. (Maybe that's partly what drove Apollo to say what he said when he first came here?) I thank you for actually reading my OP before going into auto-pilot truth-basher mode..


Hope that helps.

Your post has been helpful in the extreme. I've already saved it to my computer. Would it be OK to quote parts of it, should the need arise, on other forums?



Chris

[Apollo20]

Chris:

You do realize that if you quote JREFers on other forums people will think you have gone over to the DARK SIDE OF THE FORCE...........

[Brainache]

Chris:

You do realize that if you quote JREFers on other forums people will think you have gone over to the DARK SIDE OF THE FORCE...........

Yeah, better not quote anything by Dr Greening. I hear he posts regularly at JREF...

[chris lz]

Yeah, better not quote anything by Dr Greening. I hear he posts regularly at JREF...

It was just my polite way of saying, "thank you, I might be quoting you." :)

As for Apollo20, I hear he also sometimes quotes from Dr. Greening without credit. Very dark.

[Apollo20]

Oh dear!

Was I just hoisted by my own petard?

Ouch!

[R.Mackey]

No, not at all. I sense among some here a knee-jerk reaction that any questions regarding 9/11 science are automatically assumed to be unreasonable or disguised attempts a truther- mischief. (Maybe that's partly what drove Apollo to say what he said when he first came here?) I thank you for actually reading my OP before going into auto-pilot truth-basher mode..

I won't make excuses for anyone's bad behavior, and I myself have been known to lose my temper. Having said that, we do get a lot of Truth Movement supporters here, and some of them are singularly ill behaved. I'm sure you've heard about pdoherty who has banned here something like ten times under various disguises, for instance, or observed the continuing antics of Zen^H^H^HLast Child. It wears. Thank you for your understanding.


Your post has been helpful in the extreme. I've already saved it to my computer. Would it be OK to quote parts of it, should the need arise, on other forums?

Go right ahead. I should warn you, though, I am known to many Internet Truth Movement folks (because there really aren't that many of them, they just get around), and you're likely to get ad hominem rejections of it. But so long as it helps you understand, that's good enough. I was also serious about speaking to college professors if you want additional, unbiased perspectives. I've given that advice many times.

[chris lz]

I won't make excuses for anyone's bad behavior, and I myself have been known to lose my temper. Having said that, we do get a lot of Truth Movement supporters here, and some of them are singularly ill behaved. I'm sure you've heard about pdoherty who has banned here something like ten times under various disguises, for instance, or observed the continuing antics of Zen^H^H^HLast Child. It wears. Thank you for your understanding.

Actually, I hadn't heard about him/her. I hear you, and I not only understand, but accept that it's partly my fault, especially coming on the heels of Sizzler's thread. I guess I thought I had made it clear I was a DEBUNKER from post one. But re-reading it, I now see why it wasn't clear.

In any case, I didn't mean to criticize this forum generally on the basis of one or two chilly posts. Just new blood defensiveness, I suppose. It's a great place.


Go right ahead. I should warn you, though, I am known to many Internet Truth Movement folks (because there really aren't that many of them, they just get around), and you're likely to get ad hominem rejections of it. But so long as it helps you understand, that's good enough. I was also serious about speaking to college professors if you want additional, unbiased perspectives. I've given that advice many times.

Thanks again. About seeing a physics professor, I'm definetly going to do that one day soon, as I live next door to MIT.

[R.Mackey]

Thanks again. About seeing a physics professor, I'm definetly going to do that one day soon, as I live next door to MIT.

If you aren't currently enrolled at MIT, what I would suggest you do -- as a way to approach the professors in a favorable setting -- is to try to attend colloquia and talks of the different departments, e.g. physics and engineering. Those talks should be scheduled and posted on publicly viewable sites.

A good prof will probably be quite eager to discuss these things with someone genuinely interested in the subject, particularly a prospective student... Much better than cold-calling or just appearing in their offices. They may experience a "new blood" reaction, just like us, since some of them have been e-mail bombarded or even bullhorned by the Truth Movement in the past.

If that fails, try a community college. Much less stress, and generally good quality lecturers. And classes are cheap!

[PhantomWolf]

On the other hand, I've seen the claim that the buildings actually fell faster than free fall.

I've seen the claim that the buildings fell faster then freefall because the explosives blew all the air out of the buildings, creating a vacuum that then sucked the buildings down.

[PhantomWolf]

Yes, because it would take more energy to move that mass laterally so that it could fall through the air. Think of it as being the path of least energy change.

Thuis is extremely important and one thing that it seems the Truthers just can't understand.

Imagine a sniper shooting at a steel plate. Now it is plainly obvious that a steel has more resistance than air, so the path of least resistance must be around the steel plate right? Why then doesn't the bullet go around the plate? The answer is quite simple, it takes more energy to force the bullet to change its path so that it goes around the plate than it does to deform the point of impact enough to cause a hole and allow the bullet to pass through, and that's what it's about, energy.

The top of the buildings travelled following the path of least energy change, i.e. straight down.

[chris lz]

The "path of most resistance" in this case happens to be down


chris lz So the path of most resistance and least resistance are both down?


Gravy:
Yes, because it would take more energy to move that mass laterally so that it could fall through the air. Think of it as being the path of least energy change.


Still confused. Can someone explain why the path of most resistance isn't "sideways"? I think many people (with very bad physics intuition) would imagine falling sideways to be the path of most resistance, precisely given that it would take more energy. Is the answer that “sideways” isn’t a “path of resistance” to begin with?

Thank you

[Minadin]

I think the path of most resistance (energy change) is actually "up".

[chris lz]

. . .I suspect therefore that if you put all the papers on the WTC collapses on a physics professor's desk and asked him whether they proved that the collapses were to be expected, the most likely answer would be "Let me get back to you on that."


And once having done a little digging, do you think it likely most would come back to report they reject the truth mvt version of collapse physics?

[DannyJ]

After reading this topic, I've found that some people who ask questions are said to be truthers if they get into too much detail in their questions. I'm notreally a truther, more of someone who researches it in my free time and wonders about what hes seeing. So I'll bring something up that seems to kind of get me thinking.

On the North Tower collapse (the Eitenne video on youtube which I'm not allowed to link), if you look at the roof, you see the antenna falls a fraction of a second before the hole building gives way. This indicates the core must of been the first thing to go first (as the core supported the antenna), but the fires I saw from videos didnt seem to be that big (then again, I wasn't in the building, so I don't know the internal damage). Could it have been from the jet fuel that was said to have shot down the elevator shafts that grew bigger and bigger?

[Gravy]

After reading this topic, I've found that some people who ask questions are said to be truthers if they get into too much detail in their questions. I'm notreally a truther, more of someone who researches it in my free time and wonders about what hes seeing. So I'll bring something up that seems to kind of get me thinking.

On the North Tower collapse (the Eitenne video on youtube which I'm not allowed to link), if you look at the roof, you see the antenna falls a fraction of a second before the hole building gives way.Welcome to the forums, Danny. I'm afraid I don't see what you're seeing. It appears to me that the impact zone and the roof are falling simultaneously. Keep in mind that the collapse started by the inward buckling of the wall opposite the side from which this video was shot:

Cz6VxxVdXuA

This indicates the core must of been the first thing to go first (as the core supported the antenna), but the fires I saw from videos didnt seem to be that big (then again, I wasn't in the building, so I don't know the internal damage). Could it have been from the jet fuel that was said to have shot down the elevator shafts that grew bigger and bigger?The fires were in fact that large and severe. For instance, the portion of fire at the far right of this photo, which was taken five minutes before collapse, is larger than the entire NYC apartment building I'm in right now.

http://forums.randi.org/imagehosting/8790477b82f38893b.jpg

As experienced firefighters said,
"We were looking at two large bodies of fires that neither of us in our 33-year careers had ever seen anything that enormous." –FDNY Chief of Safety Albert Turi –Source
(http://graphics8.nytimes.com/packages/pdf/nyregion/20050812_WTC_GRAPHIC/9110142.PDF)
"It was the most unbelievable sight I ever saw, up until that point. I had been in some very busy units during my time in the fire department. I broke in, in Engine 46 and Ladder 27 in the South Bronx when the South Bronx was burning down. I was in Rescue 3, which was extremely busy; they covered the Bronx and Harlem. And then as a lieutenant, I was in the Lower East Side when that was burning down. As a captain, I was in Chinatown. I saw some unbelievable fires in Chinatown. What I saw pales in comparison (sic) to anything else I had seen previously." –FDNY Captain Jay Jonas –Source (http://archive.recordonline.com/adayinseptember/jonas.htm)

The fires were started by the jet fuel and they spread by consuming the office contents.

[Gravy]

would[/i] imagine falling sideways to be the path of most resistance, precisely given that it would take more energy. Is the answer that “sideways” isn’t a “path of resistance” to begin with?

Thank youNot sure what the issue is here. You seem to be agreeing with us. The path of most resistance would be upward, then sideways, then downward.

These simple diagrams may help you or others better understand why the "toppling" idea doesn't make sense:
A simple graphic explanation of why the top of the south tower didn't fall to the side. (http://forums.randi.org/showpost.php?p=2243709&postcount=1243)

These papers and posts discuss the issue in more detail.

Why didn't the upper part pivot about it's base? See Bazant & Zhou (2001) Appendix II (http://www.911-strike.com/BazantZhou.htm)

Eduardo Kausel (MIT): Why the Towers didn't fall like trees (http://web.mit.edu/newsoffice/nr/2001/skyscrapers.pdf)

Frank Greening: An analysis of the tipping of the upper section of WTC 2 (http://www.911myths.com/WTC2TIP.pdf) (PDF)

Physicist Dave Rogers on tipping of tower tops. (http://forums.randi.org/showpost.php?p=3178723&postcount=1)

Structural engineer "Newton's Bit" on "tipping" (http://forums.randi.org/showpost.php?p=3278462&postcount=82)

There's much more about the engineering and physics of the collapses at my site, which is linked in my signature.

[Apollo20]

DannyJ:

Collapse initiation of the North Tower is very complex and made all the more confusing by the tipping of the upper section. Certain videos mask this effect because the top section is tipping directly away from the camera. This can look like the antenna is dropping into the building (core!) BEFORE the block, (as measured from a point on the roof-line of the facade), starts to move. You need to see collapse videos from other angles to see that the tipping is quite substantial and must be included in an estimation of what falls first. Its a real chicken (antenna) and egg (roof-line) problem, but certainly not evidence of a conspiracy!

[3bodyproblem]

Welcome Chris Iz. I hope your venture into this forum has not completely tainted your views on ALL of its members. Once your make your way past the "Pit of Snakes" and pass the "Trial by Sarcastic Canadian Lawyers" there are some very informed and helpful posters willing assist you in your endevour. In reading this thread I find it interesting that a few (Dave and Ryan in particular) have encouraged you to actually present some of this material to physics profs, teachers etc. in your immediate area, as I have done in the past ;)

The response to your questions by some has been, shall we say, less than encouraging? But you'll be happy to know "typical". You're not being centered out, it seems to be par for the course around here.

As a heads up, pay particular attention to your grammatical style here and be concise in your phrasing at all times. It's much more important here than say Colbert Nation or YouTube. Your usual "neutral" style will get you in trouble.

Good to see you're still at it. PM me anytime if you have any questions. Peace (back to lurking)

[chris lz]

Not sure what the issue is here. You seem to be agreeing with us. The path of most resistance would be upward, then sideways, then downward.




Let me put it this way. If the question appeared on a physics exam, worded like this:

In the collapse of a high rise building, what would be the path of most resistance?



would the correct answer be

A up
B sideways
C down
D up, then sideways, then down
E all of the above

So far, the answers I've been given have variously been A, C and D. Can you see why that might be a bit confusing to a physics ignoramus?

Thanks

[T.A.M.]

Welcome Chris Iz. I hope your venture into this forum has not completely tainted your views on ALL of its members. Once your make your way past the "Pit of Snakes" and pass the "Trial by Sarcastic Canadian Lawyers" there are some very informed and helpful posters willing assist you in your endevour. In reading this thread I find it interesting that a few (Dave and Ryan in particular) have encouraged you to actually present some of this material to physics profs, teachers etc. in your immediate area, as I have done in the past ;)

The response to your questions by some has been, shall we say, less than encouraging? But you'll be happy to know "typical". You're not being centered out, it seems to be par for the course around here.

As a heads up, pay particular attention to your grammatical style here and be concise in your phrasing at all times. It's much more important here than say Colbert Nation or YouTube. Your usual "neutral" style will get you in trouble.

Good to see you're still at it. PM me anytime if you have any questions. Peace (back to lurking)

Heh, you forgot "Immunization with Kool-Vax".

TAM;)

[T.A.M.]

Let me put it this way. If the question appeared on a physics exam, worded like this:

In the collapse of a high rise building, what would be the path of most resistance?



would the correct answer be

A up
B sideways
C down
D up, then sideways, then down
E all of the above

So far, the answers I've been given have variously been A, C and D. Can you see why that might be a bit confusing to a physics ignoramus?

Thanks

(D) is correct, if the amount of "up" is equal in both (A) and (D) in terms of time, and if the "up" in (A) is immediately followed by down.

TAM:)

[chris lz]

Welcome Chris Iz. I hope your venture into this forum has not completely tainted your views on ALL of its members. Once your make your way past the "Pit of Snakes" and pass the "Trial by Sarcastic Canadian Lawyers" there are some very informed and helpful posters willing assist you in your endevour. In reading this thread I find it interesting that a few (Dave and Ryan in particular) have encouraged you to actually present some of this material to physics profs, teachers etc. in your immediate area, as I have done in the past ;)

The response to your questions by some has been, shall we say, less than encouraging? But you'll be happy to know "typical". You're not being centered out, it seems to be par for the course around here.

As a heads up, pay particular attention to your grammatical style here and be concise in your phrasing at all times. It's much more important here than say Colbert Nation or YouTube. Your usual "neutral" style will get you in trouble.

Good to see you're still at it. PM me anytime if you have any questions. Peace (back to lurking)


Thank you 3body. I'll keep that in mind. It took me a few days to figure out the forum's "initiation rites," and where everyone's coming from. I'm sure I overreacted, and I certainly didn't mean to paint everyone with one brush based on a few posts.

[chris lz]

(D) is correct, if the amount of "up" is equal in both (A) and (D) in terms of time, and if the "up" in (A) is immediately followed by down.

TAM:)

:confused: Looks like I better enroll in a physics course before I ask any more seemingly simple questions.

[Anti-sophist]

Let me put it this way. If the question appeared on a physics exam, worded like this:

In the collapse of a high rise building, what would be the path of most resistance?

would the correct answer be

A up
B sideways
C down
D up, then sideways, then down
E all of the above

So far, the answers I've been given have variously been A, C and D. Can you see why that might be a bit confusing to a physics ignoramus?

Thanks

The reason you are getting different answers.. and the reason the question seems confusing is because it's fundamentally ill-formed.

The term resistance has a precise meaning, scientifically, and for the purposes of our discussion its completely irrelevant. For this situation, there's no good definition of "resistance" or how one would quantify the "resistance" of the "path" that a collapsing building took. And given any reasonable definition of "resistance" there's no such way to quantify what it would be for an entire building.

The notion that objects move in the path of "least" resistance is an emergent property of systems. There are no physical laws that talk about objects traveling the path of least resistance (unless we include the behavior of an electron, and even then it's not technically true).

Now, without getting super pedantic and tossing your question in the garbage and leaving it at that, the "most" correct answer, in my view, is A. But to be certain, we'd need to define what "resistance" means...

During the actual collapse of a building, some objects will fly up, and then later sideways and down. Some will go almost straight down. Some will go sideways, then down. Each of these objects is traveling their own path of least resistance (given some reasonable definition)... and so how do I take a multitude of objects traveling different paths and somehow characterize that as a single path for the entire structure? "Average" them? That answer is gonna be alot closer to straight down than straight up.

One thing I know for certain.. is that under no circumstances can straight down be considered the path of "most" resistance, given any reasonable definition of resistance.

[Gravy]

Let me put it this way. If the question appeared on a physics exam, worded like this:

In the collapse of a high rise building, what would be the path of most resistance?As written, that question would not appear on a physics exam! :D For one thing, there are many different types of high rise construction and many different ways that a building can fail and fall.

Don't make this (or allow us to make it) more complicated than it is. In the case of the Twin Towers, the floors and their connections in the bottom part were not strong enough to support the falling mass of the top part. Therefore the collapses continued to the ground.

Keep in mind that buildings and gravity don't only interact when something goes wrong. All buildings are constantly fighting like hell to not be flattened by gravity.

[chris lz]

Now, without getting super pedantic and tossing your question in the garbage and leaving it at that, the "most" correct answer, in my view, is A. But to be certain, we'd need to define what "resistance" means...

Thanks for your reply Anti. That is precisely the kind of detailed but also comprehensible answer I hoped for when coming here.

One thing I know for certain.. is that under no circumstances can straight down be considered the path of "most" resistance, given any reasonable definition of resistance.

versus

The "path of most resistance" in this case happens to be down


So in what sense then, if any, is the latter statement correct?

[chris lz]

As written, that question would not appear on a physics exam! :D For one thing, there are many different types of high rise construction and many different ways that a building can fail and fall.

Don't make this (or allow us to make it) more complicated than it is. In the case of the Twin Towers, the floors and their connections in the bottom part were not strong enough to support the falling mass of the top part. Therefore the collapses continued to the ground.



Thanks for your input, and for the earlier links. I'll try to read them when I have time.

The reason I bring this up is not because I doubt for a moment the buildings would have fallen all the way down. It's because I run into the stock truther phrase "the buildings fell in the path of most resistance" so often, and I wanted to have a nice rebuttal available.

Given what has been said above, may I tell said truthers I've never met a debunker who thinks the towers should have fallen up? That would make my day. :D

[Dave Rogers]

And once having done a little digging, do you think it likely most would come back to report they reject the truth mvt version of collapse physics?

It might take quite a bit of digging, and a certain amount of self-education, but ultimately I can't see a rational physicist coming to any other conclusion. Ultimately, though, there's so much more than the physics that doesn't make sense about the truth movement's arguments, that it becomes a minor point.

You have to understand that the central scientific argument of the truth movement, boiled down, is, "Physics says this couldn't have happened without explosives or incendiaries". That places a burden of watertight proof on the movement, where in fact there is nothing but fallacy and supposition. A responsible physics professor who actually took the trouble to look at the evidence thoroughly and objectively couldn't fail to see this. The fact that some physics professors still achieve that failure is something I find rather depressing.

Dave

[Dave Rogers]

Let me put it this way. If the question appeared on a physics exam, worded like this:

In the collapse of a high rise building, what would be the path of most resistance?



would the correct answer be

A up
B sideways
C down
D up, then sideways, then down
E all of the above


No. The correct answer would be "This is a meaningless question that was worded by a complete idiot, and why exactly are you presuming to examine my knowledge of physics?" Suppose the falling portion were to levitate into space, orbit Jupiter three times and then pass through the centre of the Sun, finally returning to Earth and falling into its own footprint. Would that be the path of most resistance? It's certainly a path of greater resistance than any you've listed above. Paths of least resistance are a sensible concept in physics because resistance may be presumed to have a minimum of zero. Paths of most resistance are not, because it is always possible to construct an infinitely long path with infinite resistance (and, of course, zero probability of being followed).

So the best answer to anyone who claims that the towers fell through the path of maximum resistance is probably to say that "path of maximum resistance" is an absurd concept.

Dave

[Dave Rogers]

Your local physics professor probably isn't the right person to ask.

At the higher levels of physics education, we tend to become less of a generalist, more specialised in a narrower range of expertise. Hence, you'll find that someone who specialises in muon-catalysed fusion, or interface states in sillicon-silica structures (to take two examples purely at random ;)) is unlikely to remember the sort of real-world experience that's needed for a critical examination of a theory that tries to spread itself around as many disciplines as it can mis-spell. University professors tend to be very much of this stamp, so it's quite possible that, when presented with a line of argument that looks authoritative but doesn't touch on their specialist research area, they'll initially be fooled.

For a more balanced and objective view with a solid grounding in the real world, you may be better looking to someone who's used to answering off-the-wall questions from people with very different perspectives, who regularly has to express physical principles by means of real-world examples, and who has to be a generalist rather than a specialist. In other words, you're probably better off asking a high school physics teacher, whose BS meter is likely to be rather more finely tuned.

Dave

[Dave Rogers]

Given what has been said above, may I tell said truthers I've never met a debunker who thinks the towers should have fallen up? That would make my day. :D

As an aside, Jim Hoffman claims that there was more energy expended in expanding the dust clouds thrown out by the Twn Towers than the total GPE of the towers themselves, and that this energy must have come from explosives. In effect, therefore, he's the one claiming that the towers should have fallen up; that's the most likely result of a detonation that large.

Dave

[Gravy]

Given what has been said above, may I tell said truthers I've never met a debunker who thinks the towers should have fallen up? That would make my day. :DThat's actually an excellent reply, and may get them to think a bit.

[Anti-sophist]

Quote: One thing I know for certain.. is that under no circumstances can straight down be considered the path of "most" resistance, given any reasonable definition of resistance.

versus

Originally Posted by FramerDave
The "path of most resistance" in this case happens to be down


So in what sense then, if any, is the latter statement correct?

The only way I can imagine that the latter statement above being seen as correct is for what I'd consider to be irrational and unreasonable definitions of at least one of the following words: most, resistance, or down.

Part of the problem is truthers aren't very precise and tend to imply alot of things when they speak. When truthers say that the "path of most resistance" is down, they don't really mean that. What they are trying to say is that of some reasonable subset of paths, the path of most resistance is straight down. DaveRogers touched on this idea earlier. There are an infinite number of paths and presumably resistance doesn't have an upper bound.. therefore there is no path of maximal resistance when all possible paths are considered. Truthers tend to leave out their implied assumption that the paths under consideration aren't all paths, but some subset of paths they are considering. Of course what defines their reasonable subset is completely left up in the air.. and how they decided that this particular path is maximally resistant goes unmentioned.

If you pin a truther down and make him tell you exactly how and/or why the path the buildings followed they've decided to be of "most resistance" their arguments tend to fail gloriously. Most of their arguments relate to the incredibly oversimplified argument that because there is "stuff" in the way in the direction of straight down, it therefore has the most resistance (compared with other, unspoken, but presumably reasonable paths). Of course, this fundamental assumption in their argument is absurd, as it's trivial to create scenarios where the path of "least resistance" is, in fact, straight through something, as opposed to going around.

[3bodyproblem]

Well Dave's right, most profs do specialize, and unless they've been very bad and relegated to teaching Classical Mechanics for the last 10 years they may be of little use to you. Then again, profs who have been teaching Classical Mechanics for 10 years have an uncanny ability at making you feel like a complete idiot when they do explain stuff. ("What do you mean you don't know Lagrange's Method?!!?!")
But in the hallowed halls of academia Chris has a very good chance of finding a Teachers Assistant or even student very well versed in Newtonian Mechanics and more than willing to lend his or her expertise in this area. Perhaps even spark his or her interest in, for lack of a better word, "Woo Physics", creating strong allies in the war on stupidity. Plus Chris has been afforded the luxury of living in what is the modern day hotbed of physics activity, Boston. (Unless he some how makes it to Geneva, Boston must have the highest per capita concentration of physics students in the world)
So why not do it? There's nothing to lose and only knowledge to be gained. And if for some reason you recieve a cold reception in the physics department there's always the *snicker* Engineers. Those kiss asses will do anything for attention...;)

[ElMondoHummus]

Given what has been said above, may I tell said truthers I've never met a debunker who thinks the towers should have fallen up? That would make my day. :D

That's actually an excellent reply, and may get them to think a bit.


You know, if someone could get Judy Wood to change her thesis to a gravity beam, we could claim we've seen a truther think this!

Yukka yukka yukka yukka yukka...

[ElMondoHummus]

Okay, look, if those folks are going to invoke "path of most/least resistance", why don't they also admit that forces involved dictate much of this? Engineers and physicists, please correct me if I'm grasping this wrong, but: Whatever resistance the lower levels provide must be weighed against the force applied by gravity to the upper sections. At that point, this simply (blah! Simply!...:rolleyes:) becomes a calculation of the forces in question, like what Bazant's work involved. Does the force imposed by the upper sections overcome the "resistance" of the lower ones [/rhetorical question]? I realize there are threads discussing this (as well as digressions in other threads not centered on this topic), but my point is that this is the proper way to analyze the whole concept of "path of most/least resistance".

On top of that, many people invoking that argument also claim the towers should have toppled over to the side. Again, what force is acting laterally to make this happen [/second rhetorical question]? Folks who make the "toppled over to the side" argument should be asked that question as well.

[/rant]

[Newtons Bit]

There's nothing to lose and only knowledge to be gained. And if for some reason you recieve a cold reception in the physics department there's always the *snicker* Engineers. Those kiss asses will do anything for attention...;)

It's true =[

On a side note, Structural engineers are basically just physicists who have specialized in newtonian mechanics. It's all we do. Well, besides business related stuff.

[Dave Rogers]

On a side note, Structural engineers are basically just physicists who have specialized in newtonian mechanics. It's all we do. Well, besides business related stuff.

Mind you, if one of my optical switches doesn't work too well, it tends to kill rather fewer people than if one of your buildings doesn't work too well.

Dave

[chris lz]

Thanks everyone for another round of excellent answers and insights.

I'd like to return to the issue of "free fall/near free fall," as it seems to be the truthers' cleverest trick. Forget the definition of "near free fall" for now. The more fundamental truther claim is, the towers fell "too quickly." I'm under the impression this is one of the more easily refuted claims. If so, is it a matter of some basic physics equations?

[JimBenArm]

Thanks everyone for another round of excellent answers and insights.

I'd like to return to the issue of "free fall/near free fall," as it seems to be the truthers' cleverest trick. Forget the definition of "near free fall" for now. The more fundamental truther claim is, the towers fell "too quickly." I'm under the impression this is one of the more easily refuted claims. If so, is it a matter of some basic physics equations?
This silliness doesn't even need equations. Simple observation shows this to be utterly stupid. If you look at the photos, you see debris from the building falling way ahead of the main collapse front. Therefore, this claim of "freefall/near freefall", is absolute nonsense. Where anyone came up with that idiotic idea, only the FSM knows!

[Dave Rogers]

I'd like to return to the issue of "free fall/near free fall," as it seems to be the truthers' cleverest trick. Forget the definition of "near free fall" for now. The more fundamental truther claim is, the towers fell "too quickly." I'm under the impression this is one of the more easily refuted claims. If so, is it a matter of some basic physics equations?

As with everything else, there are layers to this one. In order of decreasing absurdity, they look something like this.

1. Faster than freefall. On a quick Google search last week, I found three sites with content originating in 2007 that made this claim, so claims by the truth movement that they've moved on from this assertion are as weak as the claims that they've moved on from pods or the missing 4,000 Jews. The claim is that explosives created a partial vacuum that sucked the buildings downwards. If you're talking to someone who actually needs to hear a physics argument to refute this, give up talking to them right now.

2. At freefall. This is usually backed up by reference to the NIST report, which gives times from collapse initiation to the first exterior panels hitting the ground. Not surprisingly, this refers to free falling debris, which did indeed hit the ground at the time free falling debris would be expected to hit the ground. The collapses were significantly slower than this, and the irrefutable evidence can be found - as the steely-eyed killed of the deep says - in still photos. It's a remarkably poor dynamic argument that can be refuted by a single static picture.

3. Near freefall. Now we get to the heart of the issue, which is that truthers claim that the towers fell slower than freefall, but not slowly enough. This is a classic example of the undefined inequality, where a truther argues that A is less than B, but refuses to evaluate A or B. The simple response, therefore, is to evaluate both, and show that in fact they aren't different. And this is where the argument gets serious, as you'll see from one or two current threads.

The problem here is that neither the predicted nor the actual collapse time is known to great accuracy. Actual times are based on a combination of video evidence and seismic data, because the final stages of the collapse were hidden by dust clouds, and are generally estimated to be in the range 12-16 seconds for the main collapse. Predicted times are more difficult, because the collapse was such a complex event that it is essentially impossible to model. There are various simplifications that can be made to give an estimate of the collapse times, and Frank Greening's papers give the most thorough analysis of these simplifications that I've seen - see http://www.911myths.com/html/other_contributions.html - but these rely on an understanding of the failure properties of steel that are far from trivial, and on numerical modelling (albeit simple enough that it can be done in a spreadsheet). The result is that the observed collapse times are exactly what they would be expected to be, to within the errors of both the measurement and the model.

Truther responses to this tend to take two tacks. One is to try to repeat the calculations but generate an estimate far in excess of the actual collapse time; Kenneth Kuttler and Charles Beck both do this, but their results are based on wildly inaccurate and unrealistic assumptions about the failure properties of steel. The other is to try and cast doubt on the simplifications used in the model; Major Tom, on this forum, appears to be heading this way. The problem with this argument is that it doesn't offer a line of disproof, because even if we accept these criticisms we're then back to the situation where the collapse is not amenable to modelling. Given that the truth movement is trying to prove that the collapse times cannot be consistent with gravity based collapse, this therefore invalidates their whole argument, but generally they choose not to acknowledge this minor point.

So the answer is, no, there aren't any particularly basic physics equations that help here; it's a complex situation to model, and requires detailed understanding of steel failure mechanisms. I've learned a lot about the subject on this forum, and there's still a lot I'm not up to speed on. However, so far all the evidence is that there was nothing unusual about the speed at which the Twin Towers collapsed, and any claimed evidence to the contrary has been shown to be fatally flawed.

Dave

[chris lz]

Dave, very helpful and informative, and much appreciated.

Observation: "first exterior panels to strike the ground after the collapse initiated" meaning the debris that was falling ahead of the main structure is a good point, and I didn't realize that's what they meant. Just wondering why NIST would have preceded this with the misleading question: "How could the WTC towers collapse in only 11 seconds (WTC 1) and 9 seconds (WTC 2)." That's probably caused a lot of unnecessary confusion for truthers and debunkers alike.

Follow-up question: We have heard from Leslie Robertson, NIST, Brent Blanchard, and others, that in theory a gravity driven collapse (for any building) resulting in the same approximate fall rate as the twin towers, is not surprising, but more or less expected. So forgetting the exact parameters of the twin towers collapses, is there a basic equation that shows why in theory a building may collapse as quickly as that observed on 9/11?

Thanks for your time.

[chris lz]

Follow-up question: We have heard from Leslie Robertson, NIST, Brent Blanchard, and others, that in theory a gravity driven collapse (for any building) resulting in the same approximate fall rate as the twin towers, is not surprising, but more or less expected. So forgetting the exact parameters of the twin towers collapses, is there a basic equation that shows why in theory a building may collapse as quickly as that observed on 9/11?



Follow-up to the follow-up: or if not an equation, then just a concise but detailed explanation in layman's terms.

Here's a typical exchange I see over and over again

truther: "how do you account for the absurdly fast collapse times, given all the resistance? That violates physics.

debunker response 1 "You're obviously ignorant of physics"

debunker response 2 "Show me a peer review paper supporting this"

debunker response 3 "So all, the structural engineers in the world are ignoramuses."

Instead, I'd like to be able to answer the skeptic with an uncontroversial explanation utilizing the key concepts involved, such as gravitational potential energy, and so on. I've seen bits and pieces of this explanation scattered in various posts, but not comprehensively in a short paragraph in layman's terms. If this is possible to do, I welcome anyone's suggestion.

[aggle-rithm]

Follow-up to the follow-up: or if not an equation, then just a concise but detailed explanation in layman's terms.

Here's a typical exchange I see over and over again

truther: "how do you account for the absurdly fast collapse times, given all the resistance? That violates physics.

debunker response 1 "You're obviously ignorant of physics"

debunker response 2 "Show me a peer review paper supporting this"

debunker response 3 "So all, the structural engineers in the world are ignoramuses."

Instead, I'd like to be able to answer the skeptic with an uncontroversial explanation utilizing the key concepts involved, such as gravitational potential energy, and so on. I've seen bits and pieces of this explanation scattered in various posts, but not comprehensively in a short paragraph in layman's terms. If this is possible to do, I welcome anyone's suggestion.


I tell people this: "Without having specific values for 'all that resistance' or the force of the falling structures, what is your basis for saying the collapse time is 'absurdly fast'? How do you know which value is greater?"

It doesn't help, of course.

[DavidJames]

Follow-up to the follow-up: or if not an equation, then just a concise but detailed explanation in layman's terms.

Here's a typical exchange I see over and over again

truther: "how do you account for the absurdly fast collapse times, given all the resistance? That violates physics.

debunker response 1 "You're obviously ignorant of physics"

debunker response 2 "Show me a peer review paper supporting this"

debunker response 3 "So all, the structural engineers in the world are ignoramuses."

Instead, I'd like to be able to answer the skeptic with an uncontroversial explanation utilizing the key concepts involved, such as gravitational potential energy, and so on. I've seen bits and pieces of this explanation scattered in various posts, but not comprehensively in a short paragraph in layman's terms. If this is possible to do, I welcome anyone's suggestion.I would suggest you ask them to provide the calculations supporting their assertion that the collapse times were "absurdly fast". Actually, don't ask, demand. Based on everything I've seen to date, you will either never hear from them again or they will change the subject.

[Anti-sophist]

truther: "how do you account for the absurdly fast collapse times, given all the resistance? That violates physics.

debunker response 1 "You're obviously ignorant of physics"

debunker response 2 "Show me a peer review paper supporting this"

debunker response 3 "So all, the structural engineers in the world are ignoramuses."


I don't like any of those responses.

The truther has asked a question and also made a claim. The "correct" response is to ask the truther to demonstrate this claim that the official collapse narrative would violate the laws of physics. If he can't do such a thing, he cannot conclude that the official narrative violates any laws of physics.. only that it -might-. He has failed to falsify the official narrative.

As for the question the truther asked, I think it's valid. How do we account for the speed of the collapse? One can construct -very- simple models of the collapse and solve for times on the order of those seen.. however truthers will attack these models for their absurd simplicity. Truthers don't feel the need to determine how much the simplification effected the results.. they believe it's simply enough to point out it didn't happen "exactly" like that, therefore your math is wrong. In a truther's messed up state of mind, he believes if your calculation involves any simplification at all, or if any of your assumptions clearly aren't valid, your entire calculation can be tossed out... when this simply isn't true. The burden on the truther is to demonstrate that that violated assumption renders the result meaningless. If some assumption I make in my calculation only effects the decimal-point in the third decimal place, is it really meaningless? It's simply insufficient to demonstrate that some simplying assumption is incorrect (by definition, in a sense).

If you want the simplest possible mathematical model that roughly approximates what happens in the tower, we can give you one. It's probably treating each floor as a solid mass, with a dropped mass on top, undergoing a series of compeltely inelastic collisions. It requires pretty simple algebra to solve this particular problem. People have done this. And from there... it goes upward in complexity. We can show you how it would increase in complexity and accuracy up to and including the papers from Bazant et al. which involve pretty sophisticated mathematics.

A whole mess of models in this range exist and have solutions scattered about the internet.. all of them put the collapse time in the same order of magnitude, in direct contradiction to the flawed mathematics of Judy Wood and others.

[chris lz]

If you want the simplest possible mathematical model that roughly approximates what happens in the tower, we can give you one. It's probably treating each floor as a solid mass, with a dropped mass on top, undergoing a series of compeltely inelastic collisions. It requires pretty simple algebra to solve this particular problem.


Thanks. I take it "inelastic" is key here. Is there a sample algebraic model (or whatever you'd call it) somewhere on the net I could look at- as opposed to the more complex equations I see in the WTC science papers that throw me for a loop?

[Apollo20]

chris lz:

The first thing to consider when attempting to discuss the collapse times of WTC 1 & 2 is what is meant by "fast", or "too fast".

It begs the question: How fast do people expect a structure such as one of the twin towers to fall anyway, and why?

In truth, the precise collapse times of WTC 1 and 2 are not known very well. I would say the probable error in most collapse time estimates (I have seen) is +/- 3 seconds. Thus it is no surprise that some give very low estimates ~ 10 seconds, while others have quoted figures as high as 16 seconds.

But we do know that for the first 3 - 4 seconds into each collapse, WTC 2 was moving relatively faster than WTC 1, so WTC 2 fell faster overall. Very roughly we find that the acceleration of the upper section of WTC 2 was 3/4 g, while the acceleration of WTC 1 was about 2/3 g. But remember that this is only true for the first 3 - 4 seconds of collapse which is certainly less than 1/2 of the total collapse time.

As an aside I might add that when anti-sophist says: "He has failed to falsify the official narrative", there is a problem because there really is no official narrative as to the precise collapse times.

Anyway, the fact that the upper sections of WTC 1 & 2 fell at approximately constant accelerations, (that are less than g), tells us that there was an effective resistance being offered by the buildings to the downward motion of the upper block, and this resistive force was approximately constant. This leads to the idea of an energy term E1, defined as the energy needed to collapse one floor, which must be less than the kinetic energy gained per floor by the falling upper section, for the collapse to be self-sustaining.

E1 is also the work performed by the upper block so it is a force times a distance. We can vary the resistive force anyway that appears to model the collapse mechanics. Thus we can have a force that only acts for a fraction of a second on impact, or we can have a force that acts smoothly over an entire floor height of 3.7 meters. Mathematically this may be represented by the integral of F(x)dx, but the bottom line is that you can calculate E1 and it turns out to be less than 1/2 of the available KE for the worse case of the initial upper block of ~ 15 floors for WTC 1. Hence such a model predicts a self-sustaining collapse for WTC 1 & 2.

[PhantomWolf]

Let me put it this way. If the question appeared on a physics exam, worded like this:

In the collapse of a high rise building, what would be the path of most resistance?



would the correct answer be

A up
B sideways
C down
D up, then sideways, then down
E all of the above

So far, the answers I've been given have variously been A, C and D. Can you see why that might be a bit confusing to a physics ignoramus?

Thanks

Chris, it has nothing to do with resistance. Forget resistance altogether. It is about energy change. The less energy a object has to expend or gain to follow a path, the greater the chance of the object following that path.

I'm going to repeat that again for you. The less energy an object has to expend or gain to follow a path, the more likely it is to follow that path.

So what does that mean?

Let's look at energy gain. This means that something has to add the energy to the system, in the case of a moving object we're talking about a force acting on the object. For a object in motion to change that motion (i.e. to go from falling down to going sideways) it must have a force applied to it to move it in a new direction, this is Newton's first law of motion.

How does this effect a falling building? It means that the top of the building would have to have a force applied to it to push it sideways, that means it would need energy being applied to it to change it's direction.

What applies that force? Obviously the base of the building. But there is a second part to look at. When the top of the building lands on the bottom, it applies a force to the bottom as well, it gives it some of its energy. That energy is lost to the base in the form of damage to and buckling of the floors below. If the energy lost to that activity is less than the energy required to push the top of the building sideways, then the crushing is going to happen. If to crush the base of the building requires more energy than it would to deflect it over the side, then the base would be strong enough to remain standing and would. This is the heart of the issue. Which required more energy?

A simple bit of thought will answer this for us. The top of the building weighted several hundred tonnes and was for all purposes stationary. To push it over the edge we'd have to apply a force in the order of hundreds of kN to that mass. The floors on the other hand were only designed to carry a several hundred kilograms per square meter, a force of only a few kN. The energy lost to destroying the floor was easily a magnitude smaller than what would have been required to change its direction off the top of the building, and that is why it when directly down, it quite simply took less energy to do it.

[Anti-sophist]

Thanks. I take it "inelastic" is key here.

Not really.

If we were trying to come up with the simplest possible model, we'd have to chose either completely inelastic or elastic collisions. Inelastic is what happens when two cars collide and inter-mangle so much they effectively become one object. Elastic is like when two billiard balls collide and there is a near perfect transfer of energy. Given the choice, I think everyone would agree that inelastic is the more accurate description of how collisions between sections of a building would behave.

My most naive model would consist of a bunch of floors spaced equally, and then have the top floors go into motion, and model each collision.

Either model, though, elastic or inelastic, can be run. Both answers, I suspect, will end up somewhere longer than freefall, but not by too much.

You can increase this accuracy (and complexity) by, for example, modeling that some % of the mass is "lost" over time on the way down to the ground. I might be mistaken but I think this is approximately the model in Greening's paper on 911myths. Bazant/Greening/etc put out a paper relatively recently that takes this modeling to a far more accurate level but it requires non-trivial mathematics to understand.


Is there a sample algebraic model (or whatever you'd call it) somewhere on the net I could look at- as opposed to the more complex equations I see in the WTC science papers that throw me for a loop?Alright, it's relatively straightforward but by no means simple. Basically there are two equations, one that governs the freefall between floors, and one that governs the befores and afters of the collision. This process of fall/collide repeats.. say.. 70 times.. with a starting mass of 30 "floors" and a final mass of 100 "floors". Each time you iterate the equation, you can calculate how long the falling took, and when you finish with all 70 repetitions, you add up each time, and you get an answer.

I could give you the exact equations as they aren't terrible complicated, but actually performing the operation 70 times is probably a bit tedious and is probably better left to a computer to do the actual calculation.

If you really care about the equations,

The falling: http://www.glenbrook.k12.il.us/gbssci/Phys/Class/1DKin/U1L6c.html
The colliding: http://en.wikipedia.org/wiki/Inelastic_collision

I faintly remember someone actually performing this exact calculation on a computer and posting the results. I couldn't find it after a brief search, though, so you might have more luck.

[chris lz]

Thank you Apollo.



the fact that the upper sections of WTC 1 & 2 fell at approximately constant accelerations, (that are less than g), tells us that there was an effective resistance being offered by the buildings to the downward motion of the upper block, and this resistive force was approximately constant.

Just want to make sure I understand this correctly: with only air resistance, there would have been a constant fall rate, not an increasingly faster one. And, both towers could be observed in the videos to be moving at an increasing rate as the collapses progressed. Therefore we can be sure there was significant resistance.

As the automated flight info lady says, "Did I get that right?"

[Anti-sophist]

Just want to make sure I understand this correctly: with only air resistance, there would have been a constant fall rate, not an increasingly faster one. And, both towers could be observed in the videos to be moving at an increasing rate as the collapses progressed. Therefore we can be sure there was significant resistance.

As the automated flight info lady says, "Did I get that right?"

No. The fundamental equation at play here is F=ma, or force equals mass times acceleration.

The fall rate (ie, the speed) wasn't constant. It's the speed at which the fall-rate increases (ie, the acceleration) that we are measuring.

Apollo describes an acceleration for the falling portion of the two buildings of 2/3g and 3/4g respectively. g is the acceleration due solely to gravity (no other forces, not air resistance, or any other form of resistance). So we can be sure there was significant resistance precisely because the acceleration was measurably less than g. An object encountering no resistance falls with an acceleration equal to g. Since he measured an acceleration of less than g, he could then estimate an average upward force provided by the building below.

The really short version of all that is simply this: since the buildings fell measurably slower than an object in freefall, that proves there was a significant upward force. And that force can be estimated by this difference in fall-times.

[chris lz]

If you really care about the equations,

The falling: http://www.glenbrook.k12.il.us/gbssci/Phys/Class/1DKin/U1L6c.html
The colliding: http://en.wikipedia.org/wiki/Inelastic_collision

I faintly remember someone actually performing this exact calculation on a computer and posting the results. I couldn't find it after a brief search, though, so you might have more luck.


Cool (I think). OK, so it's not as easy as I thought. But if I find the exact calculations, I'll post it. That ought to be fun as a reply: Dear truther, please explain which of these 70 calculations is wrong, and what numbers need to be changed.

[R.Mackey]

Just want to make sure I understand this correctly: with only air resistance, there would have been a constant fall rate, not an increasingly faster one. And, both towers could be observed in the videos to be moving at an increasing rate as the collapses progressed. Therefore we can be sure there was significant resistance.

As the automated flight info lady says, "Did I get that right?"

No, not quite. Air resistance is not a constant force -- it grows larger as velocity increases. At the start of the collapse, air resistance is effectively zero. (It's also negligible all the way through the collapse, because the "upper block" isn't falling through air, it's falling through building -- but that's not the question you asked.)

What Dr. Greening is saying, correctly, is that the rate of acceleration is less than "g." And it's nearly constant. That means that there are two constant forces at work. One of them is gravity. The other one acts in the opposite direction. This constant force is the resistance of the lower structure.

The collapses did get faster and faster as they progressed. They just did so with an acceleration less than gravity. This is true both at the beginning, where there cannot possibly be any significant air resistance, and at the end, where there might have been some. So the resistance is not air resistance. It's caused by the remaining structure.

For air resistance only, look at some of the perimeter pieces that fall away. Those are acted on only by gravity and air resistance. Those too fall faster and faster over time, and they hit the ground much sooner than the collapse front in the structure. This proves the strucure's resistance was much stronger than any potential air resistance.

[jaydeehess]

Thank you Apollo.



Just want to make sure I understand this correctly: with only air resistance, there would have been a constant fall rate, not an increasingly faster one. And, both towers could be observed in the videos to be moving at an increasing rate as the collapses progressed. Therefore we can be sure there was significant resistance.

As the automated flight info lady says, "Did I get that right?"

air resistance really is not significant for a massive, dense object since ma is so large compared to air resistance until the speed of that object gets very large. Besides I do not believe A20 was even refering to air resistance.

Secondly you are really mixing up Force, accelleration and velocity. They are all separate but related parameters

[chris lz]

No. The fundamental equation at play here is F=ma, or force equals mass times acceleration.

The fall rate (ie, the speed) wasn't constant. It's the speed at which the fall-rate increases (ie, the acceleration) that we are measuring.

Apollo describes an acceleration for the falling portion of the two buildings of 2/3g and 3/4g respectively. g is the acceleration due solely to gravity (no other forces, not air resistance, or any other form of resistance). So we can be sure there was significant resistance precisely because the acceleration was measurably less than g. An object encountering no resistance falls with an acceleration equal to g. Since he measured an acceleration of less than g, he could then estimate an average upward force provided by the building below.

The really short version of all that is simply this: since the buildings fell measurably slower than an object in freefall, that proves there was a significant upward force. And that force can be estimated by this difference in fall-times.


I guess I better make that trip to MIT before my next post.

[jaydeehess]

accelleration g =32 feet per second per second

At an accelleration of g an object will have a velocity of 32 feet per second after one second, 64 feet per second after 2 seconds, 96 feet per second after 3 seconds ,,, etc.


3/4 g = 24 feet per second per second
an object undergoing an accelleration of 3/4 g will then have a velocity of 24 feet per second after 1 second, 48 feet per second after 2 seconds, 72 feet per second after 3 seconds

Force = mass times accelleration

Force due to gravity is mass times g
total force is force due to mass times g minus force acting upwards
in this case total force is 25% less than force due to gravity and thus resistive force was 1/4 that of the force due to gravity alone

MIT is not required. High school physics will suffice.

[Hokulele]

I guess I better make that trip to MIT before my next post.


All you really need to understand when looking at the collapse times with a layman's eye is the relationship between distance, velocity (what you called the fall rate), and acceleration.

Distance in this case would be the height from which the collapse started.

Velocity is how much distance can be covered in a certain amount of time. For most of the calculations you will see on this topic, this will be listed in meters per second (m/s). Basically, how fast it falls. ETA: Most people call this the speed.

Acceleration measures how fast the velocity changes. This is listed in meters per second per second, also known as meters per second squared (m/s2). Think of it like measuring the effect of mashing on the gas pedal in your car. Your speed will change over time. In the case of the collapses, gravity is acting like your foot on the gas pedal, and it is basically floored so that the speed cannot change any faster. For a free fall calculation, this would be roughly 9.8 m/s2. I do not know off the top of my head what this acceleration would be for the actual collapse, as that is where the math Anti-sophist has been describing kicks in.

So the speed does change over the duration of the collapse, but the rate of that change does not vary. Hopefully this clears this up a bit. :)

[Apollo20]

Thanks guys (and gals?) for all the useful added comments to my last post.

One more point of interest is that as long as the downward force acting on the upper descending block is greater than the upward force of resistance offered by the building's structure, the collapse continues AND accelerates. In the limiting case where the downward and upward force are equal - this could happen if the building was very sturdy on the lower floors - the upper block would cease to accelerate but move with a constant VELOCITY. (This is a great example of Newton's First Law - "A body remains in its state of rest OR UNIFORM LINEAR MOTION unless acted on by an external force.)

However, as far as we can tell the upper sections of WTC 1 and 2 accelerated all the way down - but things get very fuzzy at the end of the collapse as the rubble piles up.... However, if we assume that WTC 1 was 2/3 g, and WTC 2 was 3/4g, throughout the collapse we can use the equation t = Sqrt{2h/accel} to determine a collapse time of 11.3 seconds for WTC 1 and 10.6 seconds for WTC 2. I suspect these are too low, but they give you the concept of collapse times that are short but longer than the free fall time of 9.2 seconds

[leftysergeant]

Okay, let me see if I am visualizing this correctly. Free-fall speed could only be achieved if the floors began moving as soon as the cielings hit them. They didn't, obviously, based on the correct time of 16-24 seconds that more rational investigators accept.

So say that there was resistance. This would, in the meantime, allow some force to travel sideways. This force shoves perimeter columns outward. This stresses the clips that hold the floor slabs to the walls, making them even mopre vulnerable to falling mass, perhaps separating them ahead of the arrival of the mass. But this, it seems to me, would leave segments of the perimeter structure leaning outward, accelerating , more slowly, perhaps, than the floor slabs. Because they are connected in a stepped arrangement, spanning three floors on one end and three on the other, they have to wait for all the floors to which both they and adjoining segments are attached to fall away before they go. Thus, their weight is adding kinetic energy laterally to the outside, even before they fall.

Have I accounted for something here that others have called "missing energy?"

[slyjoe]

...

For a free fall calculation, this would be roughly 9.8 m/s2. I do not know off the top of my head what this acceleration would be for the actual collapse, as that is where the math Anti-sophist has been describing kicks in.

So the speed does change over the duration of the collapse, but the rate of that change does not vary. Hopefully this clears this up a bit. :)

Well, Richard Gage thinks the acceleration due to gravity is 9.1 m/s2.:rolleyes:

[Apollo20]

I think it is ........... on Venus!

[slyjoe]

I think it is ........... on Venus!

8.8 m/s2 on Venus. Actually, he's closer to Saturn (9 m/s2).

[rwguinn]

Okay, let me see if I am visualizing this correctly. Free-fall speed could only be achieved if the floors began moving as soon as the cielings hit them. They didn't, obviously, based on the correct time of 16-24 seconds that more rational investigators accept.
erm... not quite.
Don't go "klunkity-klunk on us, lefty... There is no pause--the floors do start to move as soon as the ceilings hit--but at a lower rate than would be expected with no resistance.
(Find yourself a chunk of installed drywall that you planom tearing out, or you dont care about. Punch it with your fist, being careful to avoid studs, of course (Thinking of the idiocy of twoofer arguments helps here)
Did you fist stop, then go on?
Nope--it just slowed down, and possibly bled. If you didn't take my advice, and hit a stud, it also may have broken (and stopped, too)!


So say that there was resistance. This would, in the meantime, allow some force to travel sideways. This force shoves perimeter columns outward. This stresses the clips that hold the floor slabs to the walls, making them even mopre vulnerable to falling mass, perhaps separating them ahead of the arrival of the mass. But this, it seems to me, would leave segments of the perimeter structure leaning outward, accelerating , more slowly, perhaps, than the floor slabs. Because they are connected in a stepped arrangement, spanning three floors on one end and three on the other, they have to wait for all the floors to which both they and adjoining segments are attached to fall away before they go. Thus, their weight is adding kinetic energy laterally to the outside, even before they fall.

Have I accounted for something here that others have called "missing energy?"
Traveling sidways is not an option without some means of transfer-of-direction (An object in motion stays in motion unless acted on by an outside force). That means is generally a result to bouncing off of an inclined surface, or, in many cases, release of energy from a bent (but not yielded) steel beam (column) breaking loose from its moorings, or by buckling of members, or some of the other chaos involved in the collapse.
Again, there is "no waiting during collapse!"

[Dave Rogers]

Okay, let me see if I am visualizing this correctly. Free-fall speed could only be achieved if the floors began moving as soon as the cielings hit them. They didn't, obviously, based on the correct time of 16-24 seconds that more rational investigators accept.

Not quite. Let's take an example.

Suppose you're driving at 60mph, and you hit a stationary car which has its brakes off. The front of your car and the back of the other car will crumple. Your car will slow down and the other car will speed up, and the two of you will probably be going at about 30mph, locked together in a mess of tangled metal. That's an inelastic collision.

And that's what happened each time the falling bits of the towers hit another floor. They speeded up between floors, then as they hit the next floor they slowed down while the next floor speeded up. Nothing actually stopped, but after each impact the whole lot was going rather slower than it would have been without having to speed up the next floor down.

When you work all that out, you get about 12-14 seconds.

So say that there was resistance. This would, in the meantime, allow some force to travel sideways. This force shoves perimeter columns outward. This stresses the clips that hold the floor slabs to the walls, making them even mopre vulnerable to falling mass, perhaps separating them ahead of the arrival of the mass. But this, it seems to me, would leave segments of the perimeter structure leaning outward, accelerating , more slowly, perhaps, than the floor slabs. Because they are connected in a stepped arrangement, spanning three floors on one end and three on the other, they have to wait for all the floors to which both they and adjoining segments are attached to fall away before they go. Thus, their weight is adding kinetic energy laterally to the outside, even before they fall.

That sounds fairly close to what happened as a layman's account. Now add to that the fact that the perimeter columns on the top part pulled inwards initially, so you've got the top part falling inside the bottom part like a wedge. You'll get collisions between the top part and the columns of the bottom part, which are already leaning outwards, that will throw those falling columns out a lot further. It's a lot like making a fine cut on a pool table; the cue ball travels along the centre of the table, but sends the object ball diagonally into the corner pocket.

And that's why, when David Ray Griffin says that gravity is vertical and so it can't throw things sideways, he's being an idiot.

Have I accounted for something here that others have called "missing energy?"

Not sure. It depends who called it that, and whether it made any sense in the first place.

Dave

[rwguinn]

Not quite. Let's take an example.

Suppose you're driving at 60mph, and you hit a stationary car which has its brakes off. The front of your car and the back of the other car will crumple. Your car will slow down and the other car will speed up, and the two of you will probably be going at about 30mph, locked together in a mess of tangled metal. That's an inelastic collision.

And that's what happened each time the falling bits of the towers hit another floor. They speeded up between floors, then as they hit the next floor they slowed down while the next floor speeded up. Nothing actually stopped, but after each impact the whole lot was going rather slower than it would have been without having to speed up the next floor down.

When you work all that out, you get about 12-14 seconds.



That sounds fairly close to what happened as a layman's account. Now add to that the fact that the perimeter columns on the top part pulled inwards initially, so you've got the top part falling inside the bottom part like a wedge. You'll get collisions between the top part and the columns of the bottom part, which are already leaning outwards, that will throw those falling columns out a lot further. It's a lot like making a fine cut on a pool table; the cue ball travels along the centre of the table, but sends the object ball diagonally into the corner pocket.

And that's why, when David Ray Griffin says that gravity is vertical and so it can't throw things sideways, he's being an idiot.



Not sure. It depends who called it that, and whether it made any sense in the first place.

Dave

Better description than mine, although I like my drywall scenario best.
Allows removal of frustrations without violating any laws or decorum...

[Dave Rogers]

Better description than mine, although I like my drywall scenario best.
Allows removal of frustrations without violating any laws or decorum...

Yeah. I still have a mis-shapen bone in my left hand from an instance of that style of frustration removal over 20 years ago. It's a long story, involving far infra-red interferometry and sound absorbing foam rubber.

Dave

[leftysergeant]

Yeah. I still have a mis-shapen bone in my left hand from an instance of that style of frustration removal over 20 years ago. It's a long story, involving far infra-red interferometry and sound absorbing foam rubber.

Dave

This is one of the reasons I spend so much time at the rifle range. I don't hear very well, but I can still type and hold a knife properly for Chinese cooking.

[jaydeehess]

Okay, let me see if I am visualizing this correctly. Free-fall speed could only be achieved if the floors began moving as soon as the cielings hit them. They didn't, obviously, based on the correct time of 16-24 seconds that more rational investigators accept.


Actually a true 'free fall' cannot be obtained unless the [u]entire[u/] structure all starts moving downward at the same insant. If a section starts falling and then impacts a stationary section which instantly becomes detached from the structure then the total velocity of the now combined mass will be less than that of the initially moving section at the instant contact was made.

It arises from conservation of momentum.

Even if the first section hits a lower section that began moving sometime after the initial movement of the upper section but before the upper section reaches the starting point of the lower section the two sections will collide BECAUSE the upper section is moving faster than the lower one. When they collide their total mass velocity will be less than that of the original upper mass's velocity at the instant of contact.

[jaydeehess]

drywall punching stories......... I guess I am smarter than the average frustrated idiot. I kicked a wall rather than punch it. Missed the center of the stud but still managed to sprain my ankle as it bounced off the edge and twisted my foot to the outside past where one normally can get it to go.

I also threw a screwdriver in a fiberglass hemispheric radome enclosure.
It bounced around hitting the walls 3 times as I ducked and covered.

Live and learn lol

[leftysergeant]

Traveling sidways is not an option without some means of transfer-of-direction (An object in motion stays in motion unless acted on by an outside force). That means is generally a result to bouncing off of an inclined surface, or, in many cases, release of energy from a bent (but not yielded) steel beam (column) breaking loose from its moorings, or by buckling of members, or some of the other chaos involved in the collapse.
Again, there is "no waiting during collapse!"

Things do not always fall into a neat stack, especially if we are dealing with bendable and breakable elements like the floor slabs, pans and trusses. Add in irregularly-shaped office furnishings. We now do not have an even pile. This would deflect some materioal, still having momentum, thus the ability to transfer energy to whatever they strike, moving in random directions, but, because randomly-moving objects tend to straighten out once they have collided with enoguh objects to give them direction, they would, as I see it, tend to move outward toward the lowest concetration of other moving objects. This would pile stuff up against the insides of the walls.

[rwguinn]

Things do not always fall into a neat stack, especially if we are dealing with bendable and breakable elements like the floor slabs, pans and trusses. Add in irregularly-shaped office furnishings. We now do not have an even pile. This would deflect some materioal, still having momentum, thus the ability to transfer energy to whatever they strike, moving in random directions, but, because randomly-moving objects tend to straighten out once they have collided with enoguh objects to give them direction, they would, as I see it, tend to move outward toward the lowest concetration of other moving objects. This would pile stuff up against the insides of the walls.
Bull's eye! 10 ring for sure.
Why can't troofers not see that?

[EternalSceptic]

I have seen several statements in this thread where air resistance was said to be negligible. This is of course correct for free falling debris, but not necessarily for the towers themselves.

What I read about the progress of the collapse seems to work with two assumptions:
(I may misunderstand something)
1) The resistance of the storey which is hit by the falling part of the building is more or less constant for the whole falling height of that storey
2) It is only the resistance of the construction which decreases the falling acceleration.

well, ad 1)
IMO as soon as the fallig building part hits the next lower storey (assume this storey is still more or less intact) it will for some tens of inches have an acceleration of zero or less because an undamaged structure is still able to hold the static weight of the falling block plus built in safety factor. But after 10 inches or so I guess most of the bolts, welding and other material holding the structure together will be broken, the columns will be bent and from this moment the storey is no more than a number of steel pieces without any inner strength.
Not sure of this is clear enough in my english so I give an example: Take an empty and totally unbent beer-can and place it upright on the floor. step carefully on it - it will carry your weight (at least if you are not heavier than about 70 kp). But if you bend the sides of the can just slightly it will collapse immediately at a load of only few kp.
But at 2): inside the storey ther is quite a big amount of air, and this air must get out at a speed which is a multiple of the falling speed. At some point during the collapse the air alread partly must have reached sonic speed and due to the compression it must have become pretty hot. This airstream is methinks, at least partly responsible for debris being thrown out to the sides and also for reducing the acceleration of the falling block. It is sort of an aircushion.
The size of the footprint of the towers was if I am not mistaken some 5000 square meters, and the air, if compressed to 2 bar had a resistance of 50 000 000 kp, which is a considerable part of the weight of the falling block. To me an assumption that the air resistance prolonged the collapse tim by some 2 seconds sounds credible.

[R.Mackey]

There is no possible way in the universe you will compress the air inside the building to 2 bar (200 kPa or about 30 PSI). Exterior windows in an undamaged structure, without debris flying all over the place, can only contain about 10 kPa or so at best.

The BLBG (http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/00%20WTC%20Collapse%20-%20What%20did%20%26%20Did%20Not%20Cause%20It%20-%20Revised%206-22-07.pdf) paper adds the interesting insight that, very late in the collapse, evacuation of collapsing floors may have approached the sound barrier. There will be some "resistance" from this, naturally. However, treating the falling upper structure by the standard drag equation -- which is what is implied by "air resistance" -- is totally wrong. But since it only happens late in the collapse, it has little effect on the overall time of collapse. This force is also negligible compared to the intertial forces resulting from momentum transfer to lower floors, and to the stress caused by lower parts of the structure. A simple comparison of the masses involved will confirm this: The air contained in a WTC Tower totals about 2,000 tons, whereas the structure itself is on the order of 300,000 tons.

Had the Towers acted as a piston in a well-sealed pressure vessel, then your intuition would be correct.

[EternalSceptic]

I beg to differ:

1) You have doubled my pressure value - bar counts from 0 kp/cm², so the actual pressure is 1 kp/cm² (but maybe that was my fault, I should have mentioned that, and I do hope the exponent 2 will show up in your browser)
2) The mass of the air alone is not the only factor - it is the force necessary to accelerate this mass to about 20fold the speed of the falling block plus the additional air around the building which must also be accelerated in order to give room for the air from inside the building, the mass of the debris which is accelerated by the air rushing out, the resistance of breaking and blown away inner walls etc.

I agree that my figures are/maybe wrong - they are just guesses, but I am quite sure that, at least during the second half of the falling distance they are much less wrong than what you suggest. If we estimate the collapse time with 12 seconds then we get
an acceleration of b = 2s / t² = 820 / 144 = 5,69 m/sec²
a time until half of the height is reached of t = sqrt(2s / b) = sqrt(410 / 5,69) = 8,48 seconds
and a speed at this point of b * t = 5,69 * 8,48 = 48,25 m/sec.
The air as an average must move at least 20 times as fast to get out of the building in time, this is 960 m/sec, pretty much over sonic speed.
That means we have to accelerate a mass of 5 tons (your value for the mass of the air) from zero to 960 m/sec in about 0,08 seconds (I assume 1 storey is 4 meters high) that requires a force of 6000 tons. for the air outside to be "pushed away" we can assume another 6000 tons. I have no idea how much the debris, friction and turbulences will add to this value, my wild but for sure very low guess is something around another 10000 tons.
22000 tons alltogether - that will decrease the acceleration noticeable.
And it becomes worse the farther we come down.

[Mince]

911 dummies for physics:

http://s1.zetaboards.com/LooseChangeForums/index/

[Apollo20]

EternalSceptic:

Why do you say that "the air as an average must move at least 20 times as fast to get out of the building in time"?

And what about air being pushed down stairwells and elevator shafts and exiting from lower floors?

[EternalSceptic]

The average distance from the centre of the floor to the outside is about 20 times as big as the height of 1 storey, the air must be out of the storey in the same time it takes the storey to be smashed, so while the upper, falling block comes down about 4 meters the air must move th whole distance from the centre of the building to the outside.

(The numbers are rough estimates, just sufficient to get an idea about the order of magnitude)

And the area of elevator- shafts and stairwells is so much smaller than the area of the complete front around 1 storey (perimeter length of the building times appr 4 squaremeters) that IMO it can safely neglected for that rough estimate.

An experiment to that:

Take a perfectly straight board of about 1 square meter to a perfectly straight floor. Both should have a smooth surface and the board may be pretty heavy, say 20 kg. Put the board to an upright position and let it fall over. You'd expect a lod bang, but instead all you hear is a slighr "hsh" and the board settles down smoothly. the aircushion slows it down just before it hits the ground.

[R.Mackey]

I beg to differ:

1) You have doubled my pressure value - bar counts from 0 kp/cm², so the actual pressure is 1 kp/cm² (but maybe that was my fault, I should have mentioned that, and I do hope the exponent 2 will show up in your browser)


Ah. No, it's not the exponent, it's gauge pressure vs. absolute pressure. I see what you're saying now.

Nonetheless, no ordinary structure will allow net pressurization anywhere near 1 bar. That kind of overpressure would blast the entire structure into pieces.


2) The mass of the air alone is not the only factor - it is the force necessary to accelerate this mass to about 20fold the speed of the falling block plus the additional air around the building which must also be accelerated in order to give room for the air from inside the building, the mass of the debris which is accelerated by the air rushing out, the resistance of breaking and blown away inner walls etc.
Yes, it's not the only factor, but it's a good hand-wave. Think of momentum transfer from the structure to the air. m v is conserved. Since mair is about 0.8% of mbuilding, the momentum loss to air is just not that significant. Multiply by maybe 2 to 4 due to wake formation and turbulent dissipation, but still, it's minor.

Anyway, I agree that fluid flow could approach the sound speed at some places late in the collapse, but this still isn't going to give you a huge correction in terms of momentum or energy. Transsonic flow implies some pressurization, but this would not be contained in the structure and would not efficiently oppose collapse. Think of those lower windows as Laval nozzles, and you'll see what I mean...

[EternalSceptic]

Right:
m(building) times v(building). But m(air) times v(air). and v(air) is roughly 20 times m(building) and m(air) is not only the air inside one storey, it is also the m(air) of the air around the building which must give way. Let alone the additional energy needed for turbulences, to smash obstructions etc.

In my calculations v(air) exceeds sonic speed before the upper block is halfways down, and at supersonic speeds the air does not move like at subsonic speeds, it does not move around obstructions, instead it is compressed in front of them and streams in straight lines away from the sides. I don't say my calculations are correct - you may be more right than I. To get the real numbers we would need all the data about what was in a certain storey, how big, how heavy, where, was it fixed and how and and and.

Most likely the truth will be somewhere in the middle.

Just an afterthought:

You wrote that a pressure of 1 bar would blow the structure into pieces - Isn't that exactly what we see on the videos, debris flying to all sides with speed and distance increasing the deeper the collapse goes down. I don't say airflow is the only reason for that, snapping of columns also plays an important role and many other factors. But there are really clouds of debris coming out at high speeds, and methinks that airflow plays quite a role here.

[leftysergeant]

There appears tp have been a lot of air moving UP the corses, so the width of the floors is not as important in calculating the speed at which it must move. If the floors were breaking as they fell, some air would escape upward through the falling debris.

[EternalSceptic]

To a certain extend yes. But I guess that the air above will be pretty much filled with falling debris and to a certain degree already compressed. The problem is, that we cannot reliably look at just one storey. In the videos it can be seen that large parts of the fassade are falling off before the collaps actually reaches that place (NO, CTers, THAT IS NOT A PROOF FOR EXPLOSIONS, DON'T BE STUPID !!). Some storeys will be damaged before the collaps reaches them because of the shockwaves coming down from the smashing of the higher stories etc.

As I wrote, all that can be only rough estimates.

[R.Mackey]

Right:
m(building) times v(building). But m(air) times v(air). and v(air) is roughly 20 times m(building) and m(air) is not only the air inside one storey, it is also the m(air) of the air around the building which must give way. Let alone the additional energy needed for turbulences, to smash obstructions etc.

I mentioned this factor above. I still expect momentum losses to the air to be less than 5% of the total momentum available. The loss of kinetic energy will therefore be < 1%.


In my calculations v(air) exceeds sonic speed before the upper block is halfways down, and at supersonic speeds the air does not move like at subsonic speeds, it does not move around obstructions, instead it is compressed in front of them and streams in straight lines away from the sides. I don't say my calculations are correct - you may be more right than I. To get the real numbers we would need all the data about what was in a certain storey, how big, how heavy, where, was it fixed and how and and and.
Like lefty said, you also have to make some optimistic assumptions about alternate gas escape paths. Air will also evacuate down elevators and through windows in advance of the collapse wave. This is what conspiracy types call "squibs," for instance. I think you've overestimated the volume of air that reaches the compressible flow regime.

Just an afterthought:

You wrote that a pressure of 1 bar would blow the structure into pieces - Isn't that exactly what we see on the videos, debris flying to all sides with speed and distance increasing the deeper the collapse goes down. I don't say airflow is the only reason for that, snapping of columns also plays an important role and many other factors. But there are really clouds of debris coming out at high speeds, and methinks that airflow plays quite a role here.

Nope. The debris flow starts early in collapse, before there can be any appreciable airflow apart from the thermal plume. It's kinetic in nature. Also, at early stages of collapse, the airflow is slower -- well below sonic -- and therefore is essentially incompressible. It will have some effect pushing dust, of course, but not much pushing denser structures.

On the other hand, pressurizing the entire Tower to 15 PSI would be equivalent to a bomb of roughly 200 tons TNT equivalent. Boom!

[EternalSceptic]

You win. :)

Just one sentence about the exponent thingy - this was badly written by myself - the exponent was not meant for the absolute vs relative pressure, i just was not sure whether the power of two in the formulas later in that post will show up

like here "an acceleration of b = 2s / t² = 820 / 144 = 5,69 m/sec²" :)

HAND

[Newtons Bit]

I mentioned this factor above. I still expect momentum losses to the air to be less than 5% of the total momentum available. The loss of kinetic energy will therefore be < 1%.


Like lefty said, you also have to make some optimistic assumptions about alternate gas escape paths. Air will also evacuate down elevators and through windows in advance of the collapse wave. This is what conspiracy types call "squibs," for instance. I think you've overestimated the volume of air that reaches the compressible flow regime.



Nope. The debris flow starts early in collapse, before there can be any appreciable airflow apart from the thermal plume. It's kinetic in nature. Also, at early stages of collapse, the airflow is slower -- well below sonic -- and therefore is essentially incompressible. It will have some effect pushing dust, of course, but not much pushing denser structures.

On the other hand, pressurizing the entire Tower to 15 PSI would be equivalent to a bomb of roughly 200 tons TNT equivalent. Boom!

15 psi would be catastrophic. A 90mph wind comes in at only about 20psf, or 0.1psi.

[leftysergeant]

It still appears to me that we are leaving out a factor generated by the nature of the perimeter columns and their multi-story configuration.

We are thinking of energy as increasing according to a constant formula and moving mostly vertically. The lateral movement, though it may seem of far less significant, may be more important than has been considered in that it gains some mechanical advantage through leverage, and that it may take surprisingly little force to push the walls outward, as compared to a more conventional structure because the perimeter columns basicly formed three-to-six floor-high levers. Gotta be hard on the floor-to-column connections, right? It seems to be that it would reduce the amount of energy needed to set the next floor slab in motion. This would speed up the process somewhat, I would think.

[Apollo20]

A bit off topic, but according to an article by Chang in Civil Engineering (ASCE), published in June 1971, a 140 mph wind against the face of a twin tower was predicted to generate a pressure of about 50 psf or ~ 0.35 psi (2.2 kN/m^2) and deflect the top of the building about 1 meter.

By comparison, typical hydrocarbon fuel/air explosions generate pressures up to 120 psi, but only for a fraction of a second!

Britain's largest peace time explosion was on June 1st, 1974, at Flixborough, when 40 tons of cyclohexane ignited. The pressure at the center of the explosion was estimated to be about 360 psi or 2.5 x 10^6 Pa.

[twinstead]

Britain's largest peace time explosion was on June 1st, 1974, at Flixborough, when 40 tons of cyclohexane ignited. The pressure at the center of the explosion was estimated to be about 360 psi or 2.5 x 10^6 Pa.

Even for somebody who has no idea what cyclohexane is, this sounds like a pretty impressive explosion...

[Newtons Bit]

Even for somebody who has no idea what cyclohexane is, this sounds like a pretty impressive explosion...

It's hexane, C6H12 in a ring. Basically something between gasoline and natural gas.

[twinstead]

It's hexane, C6H12 in a ring. Basically something between gasoline and natural gas.

Ah. So probably a little flammable, huh? ;)

[jaydeehess]

While the air inside the building had to go somewhere, to simplify the collapse as, essentially, a piston driving each ceiling down on each floor is going too far IMHO.

In places air certainly could have been trapped in this fashion and produced the breaking windows and outflows seen and attributed to 'squibs' by CT's. However for the most part I would think that broken concrete slabs would not be falling horizontally for any apprecaible distance. If air pressure under any such slab did build there would be many mechanisms that would cause the slab to tilt one way or the other. To my mind, much of the internal air had debris falling through it rather than pistoning that air and that the further into collapse the more the air mixed with the debris.

Its a limited analogy but , a load of gravel being dumped into a truck box does not create a great rush of air. It generates enough movement to cause dust to rise at the sides of the box but the tailgate is never in danger of being blown off.

[leftysergeant]

I have seen gravel knock a tailgate off a truck. All that material in those towers had to go somewhere.

Excuse me if my mind seems to be wandering here. Are we treating the dust and sand-sized material as a solid?

I ask this because at some points, the dust appears to behave as a gas, and at others like a liquid. It seems to me to act mostly like a liguid as it piles up and flows up the sides of the perimeter columns until it escapes. It seems to me that it would thus put a great deal of pressure on the tops of the columns it was over-flowing, and would thus gain some mechanical advantage through leverage, thus somewhat speeding the collapse of the floors below by unpeeling the building like a banana.

If this model is accurate, does it actually alter the energy budget, as compared to a model in which it is merely the vertical force that snaps the floors loose from the columns?

[Apollo20]

I would say that a realistic MAXIMUM value for the compression ratio of the air sandwiched between two WTC floors would be ~ 1.5. If the compression of the air occurred adiabatically, (as opposed to a slow isothermal change), the gas temperature would increase by about 53 deg C. However, even such a modest temperature increase would require an energy input of about 0.5 GJ!

[chris lz]

I promise not to prolong this thread forever. If I forgot to acknowledge anyone above , thanks for all of your replies.

Below are excerpts from a poster on another forum. Any comments appreciated, as analyzing molten metal isn't my specialty.

On the substance dripping down the South Tower:

I think the generally agreed temps [in the twin towers before collapse] were in the neighborhood of 800ish F. . . .Others ( http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html , for one) dispute the temperatures given. [chris lz is aware this conflicts with the NIST report] I know that paper burns at 451 F (Ray Bradbury could tell you that), so the heat of contents burning in an oxygen-starved environment (as indicated by the dark, sooty smoke) could not have gotten the temps a whole lot higher. . . . the aluminum was on the outside and could not have had a sustained heat application, the heat actually encountered by the aluminum had plenty of opportunity to wick away, there was no evidence of paneling slagging and melting, and people are turning cartwheels to suggest that it all was a natural event. . . with weird drippy metal exactly like thermite reactions on steel on film. . . .And the aluminum was at the very exterior and easily bled heat into the atmosphere. If you want to do logical gymnastics over the facts, you can conclude that the metal was most likely aluminum. But man, that's a stretch!


Chris lz: Point me to a demonstration that the WTC aluminum construction was such that it could not have generated molten aluminum on 9/11.

Poster: . . . the details of construction are available on the web, and a basic knowledge of what metal does with locally applied heat given huge sheets of it (distributing the heat throughout), as well as an understanding of its ability to dissipate heat into the atmosphere, the fact that melted aluminum becomes silvery and not glowy (unless it's heated to near boiling, and the temps weren't remotely THAT high), combined with all I gave above, and I must conclude that very little in the way of melted aluminum would be found, and that 9/11 was engineered by people with something to gain.

Chris lz: I started a thread over at JREF a week ago. . . There are several physicists at JREF. . .I'd like to subject your ideas to them and see what they have to say.


I would love to hear from such a forum. I base my analysis of the data on logical thinking alone, pretty much.
. . .and let people know that what aluminum looks like in pools cooling has little to do with how it looks coming directly from a heat source... I have seen footage of aluminum in daylight, melted and cooling. It is silvery, not glowy.

[leftysergeant]

The "oxygen-stareved" argument does not hold water. I have fought a lot of jet fuel fires in the open air just for drill. They all smoke hideously, and they often melt aluminum and copper and glass.

[R.Mackey]

I promise not to prolong this thread forever. If I forgot to acknowledge anyone above , thanks for all of your replies.

Below are excerpts from a poster on another forum. Any comments appreciated, as analyzing molten metal isn't my specialty.

I know that paper burns at 451 F (Ray Bradbury could tell you that), so the heat of contents burning in an oxygen-starved environment (as indicated by the dark, sooty smoke) could not have gotten the temps a whole lot higher. . .

You might want to point out that this is a bunch of crap... 451 F is the auto-ignition temperature of paper, not the maximum temperature it can create. Office fires reach over 1200oC routinely. This is proven over and over again in full-scale fire tests.

Whoever this guy is, he's not impressing me with his knowledge.