WTC 1+2 top heavy?

[r2d2m2]

I have been informed that WTC 1+2 were top heavy (upper floors were heavier than lower floors). The explanation I am given is that this is down to a hat truss design. I have seen this design explained briefly in the past and the impression I got was that all floors were identical in this respect.

I also have the impression that the exterior columns were lighter towards the top (being made of thinner material).

I am not accounting for everything yet but at the moment I detect a low centre of gravity. What I am most interested in is the centre of gravity of the upper section that broke off in the first collapse (WTC 2 I think).

Can anyone set me straight?

[GlennB]

I have been informed that WTC 1+2 were top heavy (upper floors were heavier than lower floors). The explanation I am given is that this is down to a hat truss design. I have seen this design explained briefly in the past and the impression I got was that all floors were identical in this respect.

I also have the impression that the exterior columns were lighter towards the top (being made of thinner material).

I am not accounting for everything yet but at the moment I detect a low centre of gravity. What I am most interested in is the centre of gravity of the upper section that broke off in the first collapse (WTC 2 I think).

Can anyone set me straight?

Can't give you a definitive answer on the masses involved, but this is the hat truss (and of course much of this is the basic core structure) :

http://i250.photobucket.com/albums/gg274/sap-guy/hattruss.jpg

Other than that, both the outer and core columns tapered gradually from bottom to top.
As far as centre of gravity is concerned, you'd need to factor in that the floors themselves were of consistent construction, top to bottom, and that their mass becomes somewhat more significant in total mass calculations higher up the buildings.
No engineer me, but my guess would be that the c-of-g isn't far from the geometric centre for the falling section of WTC2. Perhaps a little raised for WTC1, but not much given the masses of the floors and live-loads.

[BigAl]

I have been informed that WTC 1+2 were top heavy (upper floors were heavier than lower floors). The explanation I am given is that this is down to a hat truss design. I have seen this design explained briefly in the past and the impression I got was that all floors were identical in this respect.

I also have the impression that the exterior columns were lighter towards the top (being made of thinner material).

I am not accounting for everything yet but at the moment I detect a low centre of gravity. What I am most interested in is the centre of gravity of the upper section that broke off in the first collapse (WTC 2 I think).

Can anyone set me straight?

To the extent that this may be accurate, so what?

[r2d2m2]

Can't give you a definitive answer on the masses involved, but this is the hat truss (and of course much of this is the basic core structure) :


That is the truss AND core structure?

Other than that, both the outer and core columns tapered gradually from bottom to top.


When you say tapered are you referring to the overall dimensions of the columns or just the thickness of the material?

As far as centre of gravity is concerned, you'd need to factor in that the floors themselves were of consistent construction, top to bottom, and that their mass becomes somewhat more significant in total mass calculations higher up the buildings.


Who has done these calculations?

No engineer me, but my guess would be that the c-of-g isn't far from the geometric centre for the falling section of WTC2. Perhaps a little raised for WTC1, but not much given the masses of the floors and live-loads.


I have my ones and twos all back to front (will edit OP). It is WTC1 I am interested in. So what makes you think it would have a raised centre of gravity?

[r2d2m2]

To the extent that this may be accurate,


What I have been told may be accurate? Or what I suspect may be accurate?

so what?


That depends on what is accurate.

[Gravy]

I have been informed that WTC 1+2 were top heavy (upper floors were heavier than lower floors...
Can anyone set me straight?Yes. Your informant is very, very badly informed. The construction of the top floors of the WTC is much lighter than the lower floors. For instance, the thickness of the exterior columns was about 4" on the lower floors and 1/4" on the upper. Likewise, most core columns transition from heavy box columns below to lighter wide flange columns above. Where box columns remain, they are lighter up high than below. IIRC, about 60% of the towers' steel was located from floor 15 down. All of this information is in the NIST reports.

ETA: this paper by JREF forum member Gregory Urich should be helpful to you.
Detailed Estimate of Mass and Potential Energy of World Trade Center Tower (http://wtc7lies.googlepages.com/wtc_mass_and_energy.pdf) (pdf)

And this graphic may be helpful:
http://wtc7lies.googlepages.com/NIST1-3AFig2-62-7CoreColumnSpecs1.jpg/NIST1-3AFig2-62-7CoreColumnSpecs1-full.jpg


As for the tipping of the upper portion of tower 2, these links from my site should help you:

Why didn't the towers, or the upper portions of them, topple over?


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)
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)
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)

[Macgyver1968]

Ahhh...physics...it's your friend.

I had a girlfriend that was top heavy...She used to topple over all the time when she was drunk.

[BenBurch]

Ahhh...physics...it's your friend.

I had a girlfriend that was top heavy...She used to topple over all the time when she was drunk.

:dl:

[dropzone]

Who has done these calculations?Given that the towers stood for thirty years with no suggestion of failure until two Molotov cocktails flew into them and the resulting fires weakened the structures beyond their design limits, I'd assume the guys who designed them did.

[r2d2m2]

Yes. Your informant is very, very badly informed. The construction of the top floors of the WTC is much lighter than the lower floors. For instance, the thickness of the exterior columns was about 4" on the lower floors and 1/4" on the upper. Likewise, most core columns transition from heavy box columns below to lighter wide flange columns above. Where box columns remain, they are lighter up high than below. IIRC, about 60% of the towers' steel was located from floor 15 down. All of this information is in the NIST reports.


I have alternative adjectives to describe my informant. I would certainly go a little further than ill-informed.

:eusa_liar: :alien009: :Banane31:

Am I right in thinking that the actual trusses were all identical? I am told (by someone else) that each truss had the same load bearing capabilities. This would make sense if each truss was designed to bear only a few floors.

Cheers Gravy. You are an absolute star.

:thanks

[Gravy]

Ahhh...physics...it's your friend.

I had a girlfriend that was top heavy...She used to topple over all the time when she was drunk.Hmmm...drunkenness leads to toppling...I think you've just made an important discovery about a certain physicist's personal life!

http://farm4.static.flickr.com/3547/3387034166_2241a01587_o.jpg

[dropzone]

Hmmm...drunkenness leads to toppling...I think you've just made an important discovery about a certain physicist's personal life!You dismiss this, but do you have the PRECISE amounts of alcohol fed to each floor before the collapse? NO?!?!? Then my work here is done. ;)

[Gravy]

Am I right in thinking that the actual trusses were all identical? I am told (by someone else) that each truss had the same load bearing capabilities. This would make sense if each truss was designed to bear only a few floors.Yes, above the 6th floor or so, the composite floor systems were identical, with the exception of the few mechanical systems floors that were built with I-beams to carry heavier loads.

Cheers Gravy. You are an absolute star.

:thanksCheers! (But beware that drinking and pole dancing will almost certainly end in toppling.)

[r2d2m2]

Ahhh...physics...it's your friend.

I had a girlfriend that was top heavy...She used to topple over all the time when she was drunk.


Perhaps you should reconsider prohibition.

Originally Posted (in Cloudcuckooland) by :eusa_liar:

when 200,000 tons of steel and concrete begin moving at the rate at which it did in the south tower, it is extremely difficult to stop that movement...

Especially when you figure in the estimate of the weight of the steel incorporated in to the hat truss which would have made that section very top heavy.

The only thing which makes any sense at all in that collapse is if all 47 core columns were severed simultaneously at a point considerably lower than the maintainance floor below the impact, thus pulling the top section down through the rest of the building...

Which of course would have been hidden from view by the perimeter of the building.

:dig:

[ElMondoHummus]

Ahhh...physics...it's your friend.

I had a girlfriend that was top heavy...She used to topple over all the time when she was drunk.

Did she float sans lifejacket in the water too?

:duck:

[GlennB]

I have my ones and twos all back to front (will edit OP). It is WTC1 I am interested in. So what makes you think it would have a raised centre of gravity?

Assuming you're talking about the c-of-g of the falling section only , then the question boils down to whether the extra steel in the hat truss amounts to more than the reduced steel of the thinning columns. For WTC1 this might be the case. The significance isn't obvious though, even if true. Do tell .....

[r2d2m2]

Yes, above the 6th floor or so, the composite floor systems were identical, with the exception of the few mechanical systems floors that were built with I-beams to carry heavier loads.


This is as I suspected too then. I was told that each hat truss was identical and was, therefore, able to bear the same load, which was, therefore, the weight of the entire tower. My sensors detected one deduction too many. Why would anyone put such a load on such a truss? There is more than one. They bear inwards. This hopeful deduction did not compute.

These heavy-duty trusses just highlight this.

It is good to know my computator is still computating properly.

Cheers! (But beware that drinking and pole dancing will almost certainly end in toppling.)


I am not drinking Gravy. Where I come from the taking of alcohol and the giving of applause are two separate things. You can make a toast if you like though. Just make sure you butter the right side. It has been shown that toast is more likely to land buttered side down after all.

As for the pole dance... you can have as many signs of appreciation as you like.

:clap: :thanks :clap:

[GlennB]

This is as I suspected too then. I was told that each hat truss was identical and was, therefore, able to bear the same load, which was, therefore, the weight of the entire tower. My sensors detected one deduction too many. Why would anyone put such a load on such a truss? There is more than one. They bear inwards. This hopeful deduction did not compute.



Methinks there's confusion here between hat truss and floor truss.

[r2d2m2]

Assuming you're talking about the c-of-g of the falling section only ,


I am that.

then the question boils down to whether the extra steel in the hat truss amounts to more than the reduced steel of the thinning columns.


"The" hat truss? Singular?

For WTC1 this might be the case.


WTC1 fell first right? The falling section was the larger of the two?

I get my ones and twos all muddled.

The significance isn't obvious though, even if true. Do tell .....


See the quote (from Cloudcuckooland) above. This person has been led to believe that the centre of gravity would affect the angular momentum of the falling section as it descends. It has been suggested to him that if the centre of gravity were high the section would be more inclined to turn over. This suggestion was made indirectly by suggestion of the inverse... If the centre of gravity was low the section would be more inclined to right itself. Hence the buttered toast.

At the same time it has also been suggested (by way of hint) that if a body is rotating due to angular momentum then it is possible that the centre of rotation may not necessarily be geometrically central.

And as if that were not enough it has even been made totally obvious that the conservation of angular momentum only applies in a closed system anyway (without the hindrance of things like air resistance).

My informant wants to know why the falling section didn't float off or something along those lines. Apparently the way it moves is some sort of new, fangled, smoking gun.

Basically it goes like this... The falling section does not conserve angular momentum... therefore... go on guess... it was an inside job.

Someone should stick this sucker's picture in a COM frame. His claim to fame being that his nervous system defies the zeroeth law.

:xmas0646

I'm just glad no-one has tried to tell me that the people above the impact caused the collapse by legging it to the top floor. Although at least that would make a bit more sense.

[r2d2m2]

Methinks there's confusion here between hat truss and floor truss.


Please elaborate. I am guessing the term hat truss only applies to the topmost truss (hence the hat).

[GlennB]

Please elaborate. I am guessing the term hat truss only applies to the topmost truss (hence the hat).

That's it, but we're still not talking about the topmost floor truss. The hat truss was nothing to do with the floor system. It connected the inner and outer columns for load-redistribution purposes (see diagram in post #2 - the hat truss consists of the members that are not part of the normal core system, the diagonal stuff etc).

[r2d2m2]

That's it, but we're still not talking about the topmost floor truss. The hat truss was nothing to do with the floor system. It connected the inner and outer columns for load-redistribution purposes (see diagram in post #2 - the hat truss consists of the members that are not part of the normal core system, the diagonal stuff etc).


So you think Gravy may be wrong?

The hat truss could make the detached sections top heavy?

But you seem to be saying that this is more likely in the larger of the two sections. Surely it would need a more substantial hat to offset the extra weight of thicker columns at the lower end.

[Dave Rogers]

So you think Gravy may be wrong?

The hat truss could make the detached sections top heavy?

But you seem to be saying that this is more likely in the larger of the two sections. Surely it would need a more substantial hat to offset the extra weight of thicker columns at the lower end.

This thread is in desperate need of a few definitions.

As far as I'm aware, there were four key structural components to the Twin Towers. Somebody please correct me if any of this is wrong.

(1) The core, formed from 47 columns running up the centre of the building. These varied in size, becoming progressively lighter towards the top of the building, and were welded together from sections approximately three storeys in height. These carried approximately half the weight of the building but were not designed to resist lateral loads.
(2) The perimeter, formed from 208 columns running up the outside of the building. These had the same size throughout but varied in grade of steel with height, and were formed by bolting together units three storeys in height, but with the joints staggered so that there were no weak points at every third storey. These carried the remaining building weight and also resisted lateral loads eg. wind load.
(3) The floor trusses, which as far as I'm aware were of identical strength for all floors other than the mechanical floors. These provided lateral bracing between the core and the perimeter, without which the core would not have been stable.
(4) The hat truss, which was originally intended as a support for the antenna on the top of each tower (although that projected for WTC2 was never fitted) but had a subsidiary role of transferring loads between the core and the perimeter. Each tower had only one hat truss, forming part of the structure of the top five floors only.

It's possible that the extra weight of the hat truss could have caused a falling block to be top-heavy if that block were small enough that the top weight of the hat truss was not balanced by the bottom weight of the increased column thickness. This isn't something that can be determined by guesswork or simple reasoning; the only way to find out is to look up the weights and do the maths. One thing that can be said from simple reasoning is this:

A smaller block is more likely to have been top-heavy, because there would be less thickening of the support columns. However, a smaller block has a lower ratio of height to width, so is inherently more stable; the top-heaviness is less likely, therefore, to be significant. A larger block, where the top-heaviness is more likely to be significant, is less likely to be top-heavy.

Finally, on a simple point of information, WTC2 was hit second, fell first, and had the larger falling block.

Dave

[GlennB]

So you think Gravy may be wrong?

The hat truss could make the detached sections top heavy?

But you seem to be saying that this is more likely in the larger of the two sections. Surely it would need a more substantial hat to offset the extra weight of thicker columns at the lower end.

What Dave Rogers said above.

But no, I suspect you're getting mixed up between WTC1+2. WTC1 had the smaller falling section and that was more likely (as if it matters) to be top-heavy. Which is what I said in post #2.

[sylvan8798]

This thread is in desperate need of a few definitions.

As far as I'm aware, there were four key structural components to the Twin Towers. Somebody please correct me if any of this is wrong.

(1) The core, formed from 47 columns running up the centre of the building. These varied in size, becoming progressively lighter towards the top of the building, and were welded together from sections approximately three storeys in height. These carried approximately half the weight of the building but were not designed to resist lateral loads.
(2) The perimeter, formed from 208 columns running up the outside of the building. These had the same size throughout but varied in grade of steel with height, and were formed by bolting together units three storeys in height, but with the joints staggered so that there were no weak points at every third storey. These carried the remaining building weight and also resisted lateral loads eg. wind load.
(3) The floor trusses, which as far as I'm aware were of identical strength for all floors other than the mechanical floors. These provided lateral bracing between the core and the perimeter, without which the core would not have been stable.
(4) The hat truss, which was originally intended as a support for the antenna on the top of each tower (although that projected for WTC2 was never fitted) but had a subsidiary role of transferring loads between the core and the perimeter. Each tower had only one hat truss, forming part of the structure of the top five floors only.

It's possible that the extra weight of the hat truss could have caused a falling block to be top-heavy if that block were small enough that the top weight of the hat truss was not balanced by the bottom weight of the increased column thickness. This isn't something that can be determined by guesswork or simple reasoning; the only way to find out is to look up the weights and do the maths. One thing that can be said from simple reasoning is this:

A smaller block is more likely to have been top-heavy, because there would be less thickening of the support columns. However, a smaller block has a lower ratio of height to width, so is inherently more stable; the top-heaviness is less likely, therefore, to be significant. A larger block, where the top-heaviness is more likely to be significant, is less likely to be top-heavy.

Finally, on a simple point of information, WTC2 was hit second, fell first, and had the larger falling block.

Dave

This is essentially it in a nutshell, although I believe the perimeter columns had the same outer dimension (for the architectural purposes) but used thinner steel as you got higher in the building.

As far as the angular momentum question, you can see from some of the videos that part of the top of WTC2 does indeed keep right on going over, but the building is rotating about the "base" (at the level of the damaged section) and basically collides with the bottom portion and is broken to pieces.

In order for the entire top section to roll down into the street, it would have to hit the lower section, roll about one corner (or one wall) while pulling UP and breaking all the still-connected core columns and while NOT breaking apart itself or breaking the lower section apart in the process.

If you are having trouble picturing this, imagine driving stakes through the bottom of your refrigerator to anchor it to your floor and then tipping it over. It has to rip out the stakes, and then for some period of time, it has to be supported along ONE edge rather than on all 4 feet. Neither the lower portion nor the rotating portion of the towers was in any way designed to be supported like this. Mackey has already shown that the top could not clear the bottom and roll off like some broken treetop.

So, basically, your pal doesn't have a clue.

[r2d2m2]

This thread is in desperate need of a few definitions.

As far as I'm aware, there were four key structural components to the Twin Towers. Somebody please correct me if any of this is wrong.

(1) The core, formed from 47 columns running up the centre of the building. These varied in size, becoming progressively lighter towards the top of the building, and were welded together from sections approximately three storeys in height. These carried approximately half the weight of the building but were not designed to resist lateral loads.
(2) The perimeter, formed from 208 columns running up the outside of the building. These had the same size throughout but varied in grade of steel with height, and were formed by bolting together units three storeys in height, but with the joints staggered so that there were no weak points at every third storey. These carried the remaining building weight and also resisted lateral loads eg. wind load.


So the core and perimeter columns together bore the load of everything above them. This load obviously got less further up the building and so it makes perfect sense for the capabilities of these columns to be reduced accordingly. Making upper sections just as strong as lower sections would put unnecessary load on the base, reduce the achievable height of the structure and add to the costs. And yet I am informed (by a video about the physics of 9/11) that if you took the uppermost floors of WTC1 or WTC2 and set them on the ground you would then be able to place another complete tower on top. I knew they had to be kidding me. Truth movement my arse.

You also mention a factor I like to refer to as the big bad wolf. Namely the wind. This is the first time I have ever heard my good friend being mentioned in this equation. I wonder... Are there any suggestions that Wolfie may have played a role in the events of 9/11 (other than supplying oxygen to the fires)? You say only the outer columns were designed to resist lateral load but do you know how the resultant energies were dissipated

I imagine the ultimate product of wind energy would be a movement of the entire structure (down to the base) but there may be other possibilities that I have not come across in my limited experience of high-rise buildings. My gut feeling is that weaknesses resulting from the impacts would have interfered with the buildings abilities to dissipate wind energy. I then have visions of this wind energy slowly but surely causing metal fatigue in all the wrong places. Any ideas? Just out of interest.

(3) The floor trusses, which as far as I'm aware were of identical strength for all floors other than the mechanical floors. These provided lateral bracing between the core and the perimeter, without which the core would not have been stable.


This is obviously where the video I watched has got its air brained ideas from. They must imagine that these floor trusses bear the entire load from above rather than simply transmitting a relatively small load to the vertical columns. So these were designed to transmit about 50/50 to the core and perimeter equally?

The video also described these as hat trusses and even showed the illustration that GlennB gives us. This is where my confusion between hat and floor trusses comes from.

(4) The hat truss, which was originally intended as a support for the antenna on the top of each tower (although that projected for WTC2 was never fitted) but had a subsidiary role of transferring loads between the core and the perimeter. Each tower had only one hat truss, forming part of the structure of the top five floors only.


Now this hat truss finally makes sense. I was looking at the design thinking there must be more to it than simply transmitting loads between columns. It just has a very vertical load look to it and now it is quite clear that this load would be central. The hat truss transmits this load outwards to all the core and perimeter columns evenly then?

I'm still not entirely clear on this subsidiary role though. Not that it really matters. Just a little puzzled that's all.

It's possible that the extra weight of the hat truss could have caused a falling block to be top-heavy if that block were small enough that the top weight of the hat truss was not balanced by the bottom weight of the increased column thickness. This isn't something that can be determined by guesswork or simple reasoning; the only way to find out is to look up the weights and do the maths. One thing that can be said from simple reasoning is this:

A smaller block is more likely to have been top-heavy, because there would be less thickening of the support columns. However, a smaller block has a lower ratio of height to width, so is inherently more stable; the top-heaviness is less likely, therefore, to be significant. A larger block, where the top-heaviness is more likely to be significant, is less likely to be top-heavy.


Well I do not think my informant has calculated this. He seems to be making an educated guess based on the existence of a single hat truss. At least he has that bit right. He is, however, also aware that the outer columns are thinner towards the top. Not so sure if he realises that this is also the case with the core columns too.

So anyway, it looks like the skeptics will have to do all the hard work as usual. Hopefully the data that Gravy has pointed me towards will help with this one.

Finally, on a simple point of information, WTC2 was hit second, fell first, and had the larger falling block.

Dave


It seems I had my ones and twos right in the first place then. I am definitely talking about WTC2, which was hit second, fell first, had a larger falling section and is often referred to as the south tower. Sorry for any confusion I have caused with my number mix-ups

Thank you very much for all your help. Your efforts are greatly appreciated. In fact I feel another pole dance coming on.

:thanks

[r2d2m2]

What Dave Rogers said above.

But no, I suspect you're getting mixed up between WTC1+2. WTC1 had the smaller falling section and that was more likely (as if it matters) to be top-heavy. Which is what I said in post #2.


Yes indeed. I had it right to begin with but then got it back to front by the time I got to you. Pretty sure I've got it now though. It is WTC2 I am interested in.

Cheers.

[r2d2m2]

This is essentially it in a nutshell, although I believe the perimeter columns had the same outer dimension (for the architectural purposes) but used thinner steel as you got higher in the building.


Got that.

As far as the angular momentum question, you can see from some of the videos that part of the top of WTC2 does indeed keep right on going over, but the building is rotating about the "base" (at the level of the damaged section) and basically collides with the bottom portion and is broken to pieces.


I agree that the top section goes on rotating as it descends but fail to see how the centre of rotation can be at the base once it has become separated. Where gravity is relatively uniform I would expect the centre of rotation to be much closer to the centre of gravity. This is slightly complicated by the downward motion of the section but I don't think this is enormously significant.

I should also add that strictly speaking we are talking about the centre of mass, although there is very little point splitting hairs when, as I said, we are working in a pretty uniform field.

In order for the entire top section to roll down into the street, it would have to hit the lower section, roll about one corner (or one wall) while pulling UP and breaking all the still-connected core columns and while NOT breaking apart itself or breaking the lower section apart in the process.


This isn't really a matter of it rolling off into the street. The section continues to rotate after it has broken off and as it comes more or less straight down. The question is not about why the whole thing stops going sideways into the street. It is about why it stops rotating. This is the difference between linear and angular momentum. I realise that angular momentum could lead to linear momentum but that's not what my informant is getting at.

He insists that the falling section loses angular momentum (stops rotating) completely and this arouses suspicion. I really have no idea exactly what suspect influence he thinks is responsible but he seems to be clinging to the highly theoretical notion of the conservation of momentum (which only truly stands in a closed system). Maybe he should construct a perpetual motion device to test his ideas.

It seems obvious to me that as the falling section meets with resistance from the standing section (and even the air) it is bound to lose momentum (both angular and linear). Nothing fishy there. Not that I see it losing a fat lot mind. Resistance from the standing section seems pretty ineffective once the falling section is on the move. And of course any downward momentum that is lost is quickly regained thanks to gravity. Not that my informant is concerned about this.

What concerns him is that as he watches the falling section descend it seems to stop rotating. Either that or he has a very poor grasp of what is meant by the term angular momentum.

If you are having trouble picturing this, imagine driving stakes through the bottom of your refrigerator to anchor it to your floor and then tipping it over. It has to rip out the stakes, and then for some period of time, it has to be supported along ONE edge rather than on all 4 feet. Neither the lower portion nor the rotating portion of the towers was in any way designed to be supported like this. Mackey has already shown that the top could not clear the bottom and roll off like some broken treetop.


Not the best analogy really. I'm sure that many of the stakes were weaker at the point they were attached to the fridge and simply broke off at that point (rather than being pulled up out of the ground). I think you assume that my kitchen floor provides enough resistance to allow me to lever the stakes upwards in this way. Personally I suspect that much of the damage was done by a bending/folding action rather than a pulling action (if you know what I mean).

The main thing, however, is that we are not talking about the fridge rolling off into the street anyway. Hopefully you can see what I am getting at now... the ANGULAR motion of the falling section AFTER it has become separated.

So, basically, your pal doesn't have a clue.


You got one thing wrong... He ain't no pal of mine.

Obviously we still have a couple of crossed wires but thanks for your help anyway.

[GlennB]

The main thing, however, is that we are not talking about the fridge rolling off into the street anyway. Hopefully you can see what I am getting at now... the ANGULAR motion of the falling section AFTER it has become separated.


I suspect a lot of truthers were over-impressed years ago when Dr Jones (I think it was?) first spouted about loss of angular momentum in WTC2. I recall he suggested that only an explosive intervention could cause this. Rubbish, of course, as blowing the top section to pieces wouldn't reduce its total angular momentum, just make it hard to detetct. In practice all that needs to happen is for the upper section to make contact with the lower, which it did very rapidly over a large area. The angular momentum is converted into the linear momentum of pieces flying away, but tending more to a certain direction.

The only analogy that springs to mind is that of a car spinning down an icy road and hitting a line of rubbish bins. The car's spinning is reduced as the bins get knocked sideways. I'm sure there are better analogies ;)

[r2d2m2]

I suspect a lot of truthers were over-impressed years ago when Dr Jones (I think it was?) first spouted about loss of angular momentum in WTC2. I recall he suggested that only an explosive intervention could cause this. Rubbish, of course, as blowing the top section to pieces wouldn't reduce its total angular momentum, just make it hard to detetct.


Interesting. You see my "pal" swore this was a new idea that he had come up with all by himself. So this Dr Jones is not up to Indiana's standards then? Sounds a bit thick to me.

In practice all that needs to happen is for the upper section to make contact with the lower, which it did very rapidly over a large area. The angular momentum is converted into the linear momentum of pieces flying away, but tending more to a certain direction.


I imagine that would be the case. I also imagine a fair bit of heat too.

The only analogy that springs to mind is that of a car spinning down an icy road and hitting a line of rubbish bins. The car's spinning is reduced as the bins get knocked sideways. I'm sure there are better analogies ;)


Spin a coin. Time how long it takes to lose 100% of its angular momentum due to nothing other than friction and air resistance.

Try the same thing under water. Was that one tick or two?

So we don't even need solid objects like buildings (or bins) to arrest angular momentum. They just speed the process up a little.

These truthers need to start worrying when angular momentum is sustained indefinitely... Like build me a perpetual motion machine and I will pay you three gazillion dollars. Who needs oil when you have the new physics of 9/11?

And as if this is not comical enough don't forget that a high centre of gravity is supposed to make a rotating body even more resistant to resistance (or something along those lines). Galileo is probably wondering why he bothered.

I just hope my calculations suggest a low centre of gravity. That will make this even more fun.

[sylvan8798]

G
This isn't really a matter of it rolling off into the street. The section continues to rotate after it has broken off and as it comes more or less straight down. The question is not about why the whole thing stops going sideways into the street. It is about why it stops rotating. This is the difference between linear and angular momentum. I realise that angular momentum could lead to linear momentum but that's not what my informant is getting at.

Ok. I've seen a number of truthers saying it should have rolled down into the street like a giant cubical ball (somewhere on Youtube there's a video of this, but don't ask me to find it - Gage or one of those nuts). If "pal" expects the top to keep rotating once it collides with the bottom, ask him where it would rotate to - upside down?

Going back to our inadequate analogy of the fridge it's like expecting the fridge to keep rotating once it has fallen over sideways and hit the floor. Granted, the top didn't fall all the way over sideways, but in order to do THAT it would now have to roll over an axis at the base of the exterior wall. No way this can happen.


Not the best analogy really. I'm sure that many of the stakes were weaker at the point they were attached to the fridge and simply broke off at that point (rather than being pulled up out of the ground). I think you assume that my kitchen floor provides enough resistance to allow me to lever the stakes upwards in this way. Personally I suspect that much of the damage was done by a bending/folding action rather than a pulling action (if you know what I mean).



Agreed. My point with the stakes (which I should have clarified would be through the center of the fridge floor), was to "model" the core of the building. Even assuming all the exterior columns have failed, some of the core is still connected and the horizontal axis of rotation is through the core at the elevation of the damage.

These columns have to fail before the axis would theoretically shift to the center of mass. But the top has collided with the bottom and a lot of it has broken apart before this all happens, leading to the downward momentum of the ensuing collapse. The top is now basically laying on the bottom, and can't go rotating about anywhere. And the center of mass, if it matters, is still between the center and the exterior wall.

[Grizzly Bear]

This isn't really a matter of it rolling off into the street. The section continues to rotate after it has broken off and as it comes more or less straight down. The question is not about why the whole thing stops going sideways into the street. It is about why it stops rotating. This is the difference between linear and angular momentum. I realise that angular momentum could lead to linear momentum but that's not what my informant is getting at.
In order for the rotation to translate the center of gravity outside of the building's footprint a support point has to exist, and not only exist but be capable of supporting that load long enough to translate the COG outside of the footprint. The trade centers weren't capable of doing this which would be the most important point. The columns were designed for wind loads spread across the building's exterior face and the normal gravity loads, not a gigantic localized off-plane loading condition.

Think about how an empty soda can behaves; it can sustain a significant amount of your body weight on its own, but apply a small load perpendicular to the vertical plane and put a small kink in it, and the can gets completely flattened by a small fraction of the original load. The same basic concept applies to load bearing columns.

Since the columns failed, the downward force of gravity was the dominant player. The rotation probably didn't stop, but it didn't significantly impact the outcome of the collapse.

[r2d2m2]

Ok. I've seen a number of truthers saying it should have rolled down into the street like a giant cubical ball (somewhere on Youtube there's a video of this, but don't ask me to find it - Gage or one of those nuts).


I figured where the crossed wire came from. You have come across a similar idea before and assumed this was what I was talking about. You may have been led in that direction by others who have done the same thing.

I have had a look at this idea though. It seems we have "twoofers" who insist it SHOULD DEFINITELY have gone completely sideways into the street. Then we have "duhbunkers" who insist this would be IMPOSSIBLE. I wonder if there is anyone who thinks that it could have gone EITHER WAY depending on certain variables. Variables such as the position of the falling section's centre of gravity at the moment it became detached.

If "pal" expects the top to keep rotating once it collides with the bottom, ask him where it would rotate to - upside down?


That is what he must be thinking. That an object will fall heavy end first. Maybe he should go skydiving with a lead helmet to protect his highly advanced brain. I will be asking him lots more questions too don't you worry.

Going back to our inadequate analogy of the fridge it's like expecting the fridge to keep rotating once it has fallen over sideways and hit the floor.


Not really. The fridge is standing on a tower remember. And if it was pushed off a tower in this way it would certainly go on rotating for some time. The only place it would suddenly stop when it hit horizontal (like there was a floor) and then drop straight down (like a non-rotating fridge) is Toon Town.

As the fridge goes over the edge and the centre of rotation shifts much of its momentum remains angular. But... having said that... some of it does become linear too. This is why if we tip the fridge over the edge of a tower it will kick outwards a little (and leave the building completely). This is also why if you push a fridge over on a rubber floor it may just bounce sideways a touch.

These people who think the top should have gone further sideways into the street are not entirely delusional They are simple overlooking a few details. And they are not alone.

Granted, the top didn't fall all the way over sideways, but in order to do THAT it would now have to roll over an axis at the base of the exterior wall. No way this can happen.


We can simplify it to an axis of rotation but you must keep in mind that as the section breaks loose the axis shifts towards its centre of mass. It then has its very own axis made from a very mysterious metal indeed. Then it continues to rotate around this axis all by itself (due to momentum). Provided it does not meet with too much resistance as it falls it will go horizontal, upside-down horizontal, right way up, etc, etc. Once it has started to rotate it does not need any bits of building to roll over and the only thing that can stop it is the rest of the universe.

My point with the stakes (which I should have clarified would be through the center of the fridge floor), was to "model" the core of the building. Even assuming all the exterior columns have failed, some of the core is still connected and the horizontal axis of rotation is through the core at the elevation of the damage.


If the axis of rotation were at the core then the majority of the tension would be at the exterior columns on one side. What would happen to them would depend very much on their tensile strength and/or ductility. They may well stretch rather than pulling anything up. They may just fracture immediately

Once the exterior fails at both sides the core columns would then fold and fracture themselves. If they don't fracture fairly early on the top section is definitely going to go well and truly into the street and beyond.

The fact that the top section of WTC2 did not go sideways all that much tells me that its axis shifted pretty early on, which also indicates that the core columns failed pretty early on. This suggests to me that the core columns had very little ductility (at least at that point). In fact I am inclined to think that they may even have had nil.

These columns have to fail before the axis would theoretically shift to the center of mass. But the top has collided with the bottom and a lot of it has broken apart before this all happens, leading to the downward momentum of the ensuing collapse.


I'm not so sure. I think if the core had provided a solid pivot point for any length of time the top would have tipped out further into the street. You must realise that the closer the axis is to the base the further out the top will go?

The top is now basically laying on the bottom, and can't go rotating about anywhere.


The top was laying on the bottom. Until it started moving. It can go on rotating no problem. It will not stop instantly as soon as it meets with a little resistance. If this were the case we would also expect it to stop falling. But this does not happen. It has too much momentum. It will lose angular momentum bit by bit as it works its way through air, buildings, etc. Solids, liquids and gases all provide reactive forces (equal and opposite to active forces). What varies is their ability to resist these forces.

And the center of mass, if it matters, is still between the center and the exterior wall.


It matters. Although I was under the impression that no-one had worked out where it was yet.

I think what a lot of people are missing is that much of the top of WTC2 did come down in the street well outside the buildings footprint, taking out a good part of WTC4 in the process. There is no neat pile. There is no symmetry.

The "twoofers" seem to think that this didn't happen and want to know why.

The "duhbunkers" seem to think that this didn't happen because of physics.

Personally I reckon this didn't happen to the degree that you might expect if the building was made of solid rock (for obvious reasons) but I do think it happened to a certain degree. For one thing the building did provide a solid pivot point for a short while. And I would still certainly expect it to provide greater resistance than the air as it collapsed no matter how great the forces.

New Yorkers need to count their lucky stars. If WTC2 had been a bit more substantial the destruction could have been much greater.

[sylvan8798]

I wonder if there is anyone who thinks that it could have gone EITHER WAY depending on certain variables. Variables such as the position of the falling section's centre of gravity at the moment it became detached.



Maybe if the plane had hit at the 20th floor.



These people who think the top should have gone further sideways into the street are not entirely delusional They are simple overlooking a few details. And they are not alone.

We can simplify it to an axis of rotation but you must keep in mind that as the section breaks loose the axis shifts towards its centre of mass. It then has its very own axis made from a very mysterious metal indeed. Then it continues to rotate around this axis all by itself (due to momentum). Provided it does not meet with too much resistance as it falls it will go horizontal, upside-down horizontal, right way up, etc, etc. Once it has started to rotate it does not need any bits of building to roll over and the only thing that can stop it is the rest of the universe.

If the axis of rotation were at the core then the majority of the tension would be at the exterior columns on one side. What would happen to them would depend very much on their tensile strength and/or ductility. They may well stretch rather than pulling anything up. They may just fracture immediately

Once the exterior fails at both sides the core columns would then fold and fracture themselves. If they don't fracture fairly early on the top section is definitely going to go well and truly into the street and beyond.

The fact that the top section of WTC2 did not go sideways all that much tells me that its axis shifted pretty early on, which also indicates that the core columns failed pretty early on. This suggests to me that the core columns had very little ductility (at least at that point). In fact I am inclined to think that they may even have had nil.



It is obvious to me that you believe the "truthers" on this point and are arguing their case. Perhaps you are one of them, pretending to be a skeptic and trying to lead people down the wrong path.

It is also obvious that you don't understand the physics of this, which are not that complicated. The top rotated, slammed into the bottom, broke apart, broke the bottom apart, and down she went. No giant cube rotating over and over down into the street, dude. Not a chance.


I'm not so sure. I think if the core had provided a solid pivot point for any length of time the top would have tipped out further into the street. You must realise that the closer the axis is to the base the further out the top will go?

How could it have rotated about any point other than where it was attached?

It matters. Although I was under the impression that no-one had worked out where it was yet.

I think Mackey worked that out. At something like 8 degrees tilt (sorry if I don't have the exact number), the top hits the bottom. At 8 degrees, a COG in roughly the center, say 200 feet above the pivot, has moved about 28 feet. Need to go AT LEAST 35 FEET to the nearest exterior from the edge of the core. So even if it is rotating about an axis through the edge of the core (not really likely), it is NOT over the edge of the building.


Personally I reckon this didn't happen to the degree that you might expect if the building was made of solid rock (for obvious reasons) but I do think it happened to a certain degree. For one thing the building did provide a solid pivot point for a short while. And I would still certainly expect it to provide greater resistance than the air as it collapsed no matter how great the forces.

Cubical rocks don't roll well.


New Yorkers need to count their lucky stars. If WTC2 had been a bit more substantial the destruction could have been much greater.

How so?

[r2d2m2]

It is obvious to me that you believe the "truthers" on this point and are arguing their case.


That's funny because I am arguing AGAINST a truther who seems to have similar views to you... that the upper section stopped rotating. The only difference is the conclusions you draw from this.

Perhaps you are one of them, pretending to be a skeptic and trying to lead people down the wrong path.


That's even funnier because this truther reckons I am a government agent.

What I see are truthers AND skeptics leading people down wrong paths. Being at war with a bad guy does not, IN ANY WAY, make you a good guy. And arguing that grass must be green because it is not blue does not, IN ANY WAY, make you clever.

Who's side am I on? If only things were that black and white.

It is also obvious that you don't understand the physics of this, which are not that complicated.


Oh please. The physics of this are extremely complex. This is the truther's problem and this is your problem... oversimplification.

The top rotated, slammed into the bottom, broke apart, broke the bottom apart, and down she went.


When the top began rotating it was already in contact with the bottom. No-one pulled a piece out to give the top room to move. Forces acting between both parts caused them to start breaking and so the rotation PROGRESSED. One may well have broken more than the other due to the angle of attack but neither completely disintegrated straight away. And the easier they broke the MORE LIKELY it would be that the top would CONTINUE to rotate. What on earth makes you think that something would lose all of its angular momentum by simply crashing into something that was stationary?

How could it have rotated about any point other than where it was attached?


You have proved my point... it ain't just truthers who are muddled.

The planet you live on has angular momentum. It is rotating. But it is not rotating around some solid axle to which it is attached. It is rotating around its CENTRE OF MASS. And this is because it is not attached to ANYTHING. Now how much steel and concrete do you think it would take to instantly stop it from spinning? You think it will stop as soon as it hits something regardless how how much energy this something is able to absorb before it gives way? You and I must be living on different planets altogether.

I think Mackey worked that out.


Mackey worked out where the centre of gravity was?

At something like 8 degrees tilt (sorry if I don't have the exact number), the top hits the bottom.


I take it you mean that at 8 degrees the outside edge of the top section was one floor level down. This is the floor that someone replaced with thin air to allow the rotation to start?

But that is by the by because if you think the thing stopped at 8 degrees then you need to think again. I have a picture of WTC2 just before it disappears into a cloud of dust and it is inclined at an apparent angle of 17 degrees. But this picture was not taken totally square on, which means that the actually angle is EVEN GREATER. Having said that it is not far off and so we are probably talking 20 degrees tops. This is a fair bit more than Mackey's model suggests though. Is it not?

I'd rather not say what I think about this model. Mackey may get upset.

At 8 degrees, a COG in roughly the center, say 200 feet above the pivot, has moved about 28 feet.


That's IF the COG is halfway up the section. Have you worked this out or are you guestimating?

Need to go AT LEAST 35 FEET to the nearest exterior from the edge of the core.


Not sure what you mean.

So even if it is rotating about an axis through the edge of the core (not really likely), it is NOT over the edge of the building.


You are on to something. I think. It's hard to tell. This "edge of the core" could be either edge. Imagine this section is going clockwise. Are we talking about the left edge or the right edge?

Cubical rocks don't roll well.


Firstly... we are not talking about a cuboid. One of the corners has been smashed to pieces. Like you said yourself.

Secondly... if you stand a fridge on a steep enough incline then you had better hope it has a low centre of gravity. Otherwise it is going to tip over.

Thirdly... if you stand a well balanced cube on a steep enough incline it is going to ROLL all the way down.

Fourthly... you are confusing rolling and rotation anyway. These are similar but not entirely the same.

Fifthly... if our planet was a cube it would continue to ROTATE just fine.

How so?


Think real hard. You might just get it.

So no, I don't put my trust in "twoofers" or "duhbunkers". I put my trust in protractors.

[sylvan8798]

New Yorkers need to count their lucky stars. If WTC2 had been a bit more substantial the destruction could have been much greater.

Since everything in the complex was pretty much destroyed, it couldn't really have gotten worse in your "keeps on rotating" scenario.

Statements like this are a dead giveaway, trutherboy.

[GlennB]

New Yorkers need to count their lucky stars. If WTC2 had been a bit more substantial the destruction could have been much greater.

Given that the destruction was total, it's hard to understand this comment.

[r2d2m2]

Given that the destruction was total, it's hard to understand this comment.


Well Glenn, I will explain what I mean since you are asking in a polite, rational manner.

The destruction of WTC1&2 was total. This is true.

But, having said that, the destruction did not end there. You have the collapse of WTC7 for a start. I guess it depends on what you class as total.

What I am saying is that if WTC1&2 had not come down the way they did the destruction could have been even more WIDESPREAD.

Maybe there are truthers out there that recognise this fact and use it to support their controlled demolition ideas. This does not mean that anyone else who acknowledges this fact draws the same conclusions.

I for one do not not think that it came down to explosives. In fact I don't think it was intentional at all. These buildings were not designed to collapse like this. No-one had planned it to happen this way.

So personally I class it as good fortune. Not that the towers collapsed. This was very unfortunate. But that they collapsed in such a way that the damage was relatively contained.

Had WTC2 been hit a little lower, had a higher centre of gravity and/or been less prone to disintegrate then things could have gone differently. There could have been even more damage to surrounding buildings and (especially in this case) there could also have been more casualties.

I am sure there were people down below who saw the top of WTC2 toppling towards them and momentarily considered themselves dead. So I won't even say that New Yorkers need to count their lucky stars. I will assume that there are New Yorkers who have already done so several times over.

And anyone who thinks this is some kind of "inside job" argument needs to get a grip. Since when have lucky stars been on the government payroll?

JREF. A place to discuss skepticism, critical thinking, the paranormal and science in a friendly and lively way. I am starting to wonder.

[sylvan8798]

What I am saying is that if WTC1&2 had not come down the way they did the destruction could have been even more WIDESPREAD.



You say this, and yet you still have not specified exactly HOW you envision this might have taken place...

[sylvan8798]

When the top began rotating it was already in contact with the bottom. No-one pulled a piece out to give the top room to move. Forces acting between both parts caused them to start breaking and so the rotation PROGRESSED. One may well have broken more than the other due to the angle of attack but neither completely disintegrated straight away. And the easier they broke the MORE LIKELY it would be that the top would CONTINUE to rotate. What on earth makes you think that something would lose all of its angular momentum by simply crashing into something that was stationary?


Did I ever say that? The top broke into pieces. Some of those pieces continued along the same trajectory. The main part stopped rotating, so, obviously, it lost its angular momentum.

You have proved my point... it ain't just truthers who are muddled.

The planet you live on has angular momentum. It is rotating. But it is not rotating around some solid axle to which it is attached. It is rotating around its CENTRE OF MASS. And this is because it is not attached to ANYTHING. Now how much steel and concrete do you think it would take to instantly stop it from spinning? You think it will stop as soon as it hits something regardless how how much energy this something is able to absorb before it gives way? You and I must be living on different planets altogether.

I was referring to the TOP OF THE TOWER. Now you are talking about the planet. Way to stay on topic. Where do YOU think it was rotating about?


I take it you mean that at 8 degrees the outside edge of the top section was one floor level down. This is the floor that someone replaced with thin air to allow the rotation to start?


Are you contradicting yourself? You just said the top was already in contact with the bottom. And what is this *& about "someone replaced with thin air"? Are you a no-planer as well?

That's IF the COG is halfway up the section. Have you worked this out or are you guestimating?


Guesstimate, not an unreasonable one.

Since you think the top should/could/would have done something ELSE, what do you deduce from the fact that it didn't?

[r2d2m2]

You say this, and yet you still have not specified exactly HOW you envision this might have taken place...


First have a look at this video clip...

http://www.youtube.com/watch?v=UvmecjFmVyY

You should be able to see the rotation that I envision being even more pronounced under certain conditions. The falling section reaches a good 17 degrees (off vertical) before it vanishes. It could have been less. It could have been more. Depending on a number of variables.

Now consider what Professor Eduardo Kausel (MIT) tells us...

"In essence then, the towers did not collapse like trees because the structures, despite their strength, were too fragile to sustain such motions."

Now it seems we have two polarized schools of thought...

(1) The towers should have come straight down.

(2) The towers should have toppled over like trees.

I am suggesting a third possibility that MATCHES THE EVIDENCE....

(3) The towers should have done something in between.

So we are talking about varying degrees of rotation or varying degrees of tree-like behaviour. Had WTC2 been even more fragile it may have toppled less. Had WTC2 been less fragile it may have toppled more.

And fragility is not the only variable that could have had an influence.

[GlennB]

Now it seems we have two polarized schools of thought...

(1) The towers should have come straight down.

(2) The towers should have toppled over like trees.

I am suggesting a third possibility that MATCHES THE EVIDENCE....

(3) The towers should have done something in between.



Your claim in (1) is merely a simplification of the general view, given that the rotation of both upper blocks was of no great importance in collapse progress. To state that "The towers should have come straight down" is not wrong in any significant sense.

And we've already discussed the fact that angular momentum can convert to linear momentum through impact with another body or bodies. The upper section of WTC2 did have angular momentum so (3) above is bound to be true. But who is denying it? The degree of assymetrical spread of debris could even, I suppose, be estimated.

Finally, nobody but a total imbecile would image the towers falling over like trees. So setting this as one of the limits in your analysis above is rather odd, and all you seem to have achieved is to create a kind of strawman situation to demonstrate your own perspicacity.

In what way is all of this (plus your observations in the other thread, on steel temperatures being raised by aircraft debris impact) not purely academic? The buildings fell through impact damage plus the effects of fire. This is known, so what do your lines of thought and questioning in these two threads hope to add to that?

[r2d2m2]

Did I ever say that? The top broke into pieces. Some of those pieces continued along the same trajectory. The main part stopped rotating, so, obviously, it lost its angular momentum.


Well from where I'm standing you just said it again. The top section lost its angular momentum? If you think this is the case then how do you explain the shower of debris coming down at an angle towards Liberty Plaza, well away from the tower itself? Watch that clip carefully. It seems the top section breaks up somewhere in amongst the dust cloud. Some of the debris goes sideways as the angular momentum of the whole becomes linear momentum of the pieces. This is exactly the same as swinging something around and then letting go.

I was referring to the TOP OF THE TOWER. Now you are talking about the planet. Way to stay on topic. Where do YOU think it was rotating about?


It is exactly the same thing. They are both massive bodies with angular momentum. They are not attached to anything. They are not rolling over or around anything fixed or solid. They are rotating about their centre of mass. This is how all bodies with angular momentum behave. The planet is a prime example. Would you like an example that is more down to earth? Are you sure you know what is meant by angular momentum? And if so then why are you asking this question?

Are you contradicting yourself? You just said the top was already in contact with the bottom. And what is this *& about "someone replaced with thin air"?


I was being sarcastic. You seem to be implying that the rotation started because the top had freedom to rotate before it crashed into the bottom but then stopped rotating when the two connected. Like the top can rotate through thin air but not thick steel and concrete. It just isn't that simple. The top initially gains angular momentum because gravity accelerates it around a pivot point. Once the pivot point is gone it will stop gaining angular momentum but, at the same time, it will take a while for that momentum to be completely lost again. It will not happen instantly.

Are you a no-planer as well?


You are getting a little carried away with your insults. I will put it down to immaturity this time but if you keep it up we will be ending this conversation.

Guesstimate, not an unreasonable one.


Well not an unreasonable guestimate I suppose. I suspect it was slightly lower myself though. Not that this would undermine your argument that it stayed inside the perimeter. Quite the opposite. It would seem you're assuming that my ideas have something to do with it going outside. I assure you that that is not the case.

Since you think the top should/could/would have done something ELSE, what do you deduce from the fact that it didn't?


I certainly don't think it should have done something else. This is you jumping to the conclusion that I am a truther. It reminds me a lot of paranoia. You are seeing things that aren't really there.

I do, however, think it could have done something else if some of the variables had varied. Perhaps, for example, if it had been top heavy as my pal suggests. This is nothing to get your knickers in a twist over though.

And what do I deduce from the fact that it didn't do something else? Is this a trick question? Are you waiting for me to deduce that it must have been brought down with explosives? Or what?

I am trying to get to the bottom of why it did what it did so that I can correct someone who thinks it should have done something different.

You are not helping. You are up in my face like you need a truther to fight with but have trouble finding the real thing. Perhaps you should try the Loose Change forums instead. You will find plenty of no-planers to take your frustrations out on. Domenik DiMaggio should keep you going for at least a month all by himself.

Here's what I think you need to grasp... If you provide me with information that I find unsatisfactory I am going to tell you. This does not make me a truther. This makes me someone who thinks. Critically. Or do you think we should only apply critical thought to no-planer ideas?

[tsig]

Well from where I'm standing you just said it again. The top section lost its angular momentum? If you think this is the case then how do you explain the shower of debris coming down at an angle towards Liberty Plaza, well away from the tower itself? Watch that clip carefully. It seems the top section breaks up somewhere in amongst the dust cloud. Some of the debris goes sideways as the angular momentum of the whole becomes linear momentum of the pieces. This is exactly the same as swinging something around and then letting go.




It is exactly the same thing. They are both massive bodies with angular momentum. They are not attached to anything. They are not rolling over or around anything fixed or solid. They are rotating about their centre of mass. This is how all bodies with angular momentum behave. The planet is a prime example. Would you like an example that is more down to earth? Are you sure you know what is meant by angular momentum? And if so then why are you asking this question?




I was being sarcastic. You seem to be implying that the rotation started because the top had freedom to rotate before it crashed into the bottom but then stopped rotating when the two connected. Like the top can rotate through thin air but not thick steel and concrete. It just isn't that simple. The top initially gains angular momentum because gravity accelerates it around a pivot point. Once the pivot point is gone it will stop gaining angular momentum but, at the same time, it will take a while for that momentum to be completely lost again. It will not happen instantly.




You are getting a little carried away with your insults. I will put it down to immaturity this time but if you keep it up we will be ending this conversation.




Well not an unreasonable guestimate I suppose. I suspect it was slightly lower myself though. Not that this would undermine your argument that it stayed inside the perimeter. Quite the opposite. It would seem you're assuming that my ideas have something to do with it going outside. I assure you that that is not the case.




I certainly don't think it should have done something else. This is you jumping to the conclusion that I am a truther. It reminds me a lot of paranoia. You are seeing things that aren't really there.

I do, however, think it could have done something else if some of the variables had varied. Perhaps, for example, if it had been top heavy as my pal suggests. This is nothing to get your knickers in a twist over though.

And what do I deduce from the fact that it didn't do something else? Is this a trick question? Are you waiting for me to deduce that it must have been brought down with explosives? Or what?

I am trying to get to the bottom of why it did what it did so that I can correct someone who thinks it should have done something different.

You are not helping. You are up in my face like you need a truther to fight with but have trouble finding the real thing. Perhaps you should try the Loose Change forums instead. You will find plenty of no-planers to take your frustrations out on. Domenik DiMaggio should keep you going for at least a month all by himself.

Here's what I think you need to grasp... If you provide me with information that I find unsatisfactory I am going to tell you. This does not make me a truther. This makes me someone who thinks. Critically. Or do you think we should only apply critical thought to no-planer ideas?

You seem about two posts from being bannned.

[sylvan8798]

It is exactly the same thing. They are both massive bodies with angular momentum. They are not attached to anything. They are not rolling over or around anything fixed or solid. They are rotating about their centre of mass. This is how all bodies with angular momentum behave. The planet is a prime example. Would you like an example that is more down to earth? Are you sure you know what is meant by angular momentum? And if so then why are you asking this question?

Angular momentum is defined as L = r X p, where r is a position vector from the body to the ORIGIN or point about which the body is rotating, p is the linear momentum of the body, and you are taking the cross product. The ORIGIN does not have to be the center of mass, or even on the body. The earth has angular momentum about its center of mass and about the sun as well. When the top of the building begins to tilt, it is most certainly still connected to the bottom. The position vector would be from that pivot point where it is still connected to the center of mass of the top.



The top initially gains angular momentum because gravity accelerates it around a pivot point. Once the pivot point is gone it will stop gaining angular momentum but, at the same time, it will take a while for that momentum to be completely lost again. It will not happen instantly.

There is no physical reason why a body can't go from rotating to linear motion virtually instantaneously.

I certainly don't think it should have done something else. This is you jumping to the conclusion that I am a truther. It reminds me a lot of paranoia. You are seeing things that aren't really there.

If you don't have a problem with what it did, I'm not sure what the point is you are trying to make. Everyone agrees that the building tilted and then fell downward. So it wasn't 100% a downward thing or 100% a toppling thing.


I do, however, think it could have done something else if some of the variables had varied. Perhaps, for example, if it had been top heavy as my pal suggests. This is nothing to get your knickers in a twist over though.


The big variable that would influence this is the length of the moment arm, r. If it were "top heavy", or if it had been hit much lower, and the arm were longer, the angular momentum would be larger, and it might have reached an overturning moment that would have carried more of top out over the edge. The north tower also tilted somewhat as the collapse started, but since there was a much smaller section, the angular momentum was not as large.

[r2d2m2]

You seem about two posts from being bannned.

So I have people calling me "truther boy" and insinuating that I'm a "no-planer" (which I take as a severe personal insult) and yet I am the one who is two posts from being banned?

What exactly do you think I will be banned for?

[psikeyhackr]

I have been informed that WTC 1+2 were top heavy (upper floors were heavier than lower floors). The explanation I am given is that this is down to a hat truss design. I have seen this design explained briefly in the past and the impression I got was that all floors were identical in this respect.

I also have the impression that the exterior columns were lighter towards the top (being made of thinner material).

I am not accounting for everything yet but at the moment I detect a low centre of gravity. What I am most interested in is the centre of gravity of the upper section that broke off in the first collapse (WTC 2 I think).

Can anyone set me straight?
.
Actually, NO!

Now this demonstrates how good the information is and how well it has been distributed in nearly EIGHT YEARS.

Go to Lon Waters' site to see the cross sections of the columns over the height of the towers.

http://wtcmodel.wikidot.com/system:list-all-pages

I think it is impossible to make a top heavy skyscraper stand and withstand the wind. I have been demanding a table specifying the TONS of STEEL and TONS of CONCRETE on every level since the cows went home. Some people here say it is irrelevant.

There were more than 2500 exterior wall panels on each tower. the NCSTAR1 report says 12 different grades of panel were used but they do not tell us the quantity and weight of each type. An article fron an engineering magazine in 1970 says the heaviest type was 22 tons but that is all the information I have encountered about it.

We don't have information on the weight of the beams connecting the core columns either so this entire business is an idiotic mess. We are waiting for Ryan Mackey to build us a scaled model. But I think the distribution of mass had to significantly affect the outcome.

http://www.youtube.com/watch?v=z0kUICwO93Q

http://www.youtube.com/watch?v=LXAerZUw4Wc

psik

[r2d2m2]

Angular momentum is defined as L = r X p, where r is a position vector from the body to the ORIGIN or point about which the body is rotating, p is the linear momentum of the body, and you are taking the cross product.


That's if you're talking about an individual particle. I'm guessing you googled this equation and missed that small point. Think about it for one second. If we are talking about a body like a planet rotating around its centre of mass then what is r? It can't be zero because to get the cross product (r x p) you start with the product of their magnitudes (rp). And if r is zero then p becomes meaningless (as 0p = 0). It can't be the radius of the body either because not all of the mass is located at that position.

I will give you 10/10 for effort though. Nice try. But this is not the way to combat truthers. I heard you can fight fire with fire but I don't think that applies in this instance.

The ORIGIN does not have to be the center of mass, or even on the body.


No kidding. I have already talked about the centre of rotation shifting from one place to another as the core columns broke so obviously I am aware of this. The funny thing is that when I did mention it you asked me this question...

"How could it have rotated about any point other than where it was attached?"

It is nice to see you've changed your tune. It's just a shame the way you've gone about it.

I also notice you've learnt a new WORD. More evidence of some last minute studies. Centre of rotation is a perfectly acceptable (and more meaningful) term too. So no need for the CAPS.

The earth has angular momentum about its center of mass and about the sun as well.


Indeed. The entire solar system has angular momentum. It too is rotating around its centre of mass, which (strictly speaking) is not the sun. And the solar system is part of a galaxy that is rotating around another centre of mass, which (not so strictly speaking) is a super massive black hole somewhere in the regions of Sagittarius

When the top of the building begins to tilt, it is most certainly still connected to the bottom.


Yes. The top is connected to the bottom to begin with. We agree on that. All I have said is that when it becomes detached it continues to rotate. This is where we disagree.

The position vector would be from that pivot point where it is still connected to the center of mass of the top.


If the top was a single particle.

There is no physical reason why a body can't go from rotating to linear motion virtually instantaneously.


First of all the two things are not mutually exclusive. The top could (AND DID) rotate and descend at the same time. It is not a case of going from one to the other. It is case of one (angular) being lost virtually instantaneously (or not). For this to happen you need a large enough force to counter the momentum.

But we are talking about a specific situation. And in this situation that force just wasn't available. This is due to insufficient resistance in the building structure. The forces were too great for the building to cope with without giving way. It is like sitting an elephant on a deckchair. The forces on the chair will be too great and it will collapse. This analogy isn't perfect because the elephant will accelerate due to gravity when the chair breaks but hopefully you get my drift.

If you don't have a problem with what it did, I'm not sure what the point is you are trying to make.


When are you going to realise?

I AM NOT TRYING TO MAKE A POINT.

See the last character in the thread title? I asked a question. Some people did there best to try and answer the question and left it at that (gotta love Gravy). Others choose to make a song and dance routine out of it.

If you want to debate then I'm all for it but I am not interested in making points.

Everyone agrees that the building tilted and then fell downward. So it wasn't 100% a downward thing or 100% a toppling thing.


Well you and I more or less agree but we can't speak for everyone. The one thing we don't agree on is that the rotation and descent were two isolated motions. Your theory suggests that it tilted 8 degrees, stopped tilting and then began to descend. My observations suggest that it continued to rotate as it descended. I'm not trying to make a point though. I'm just trying to get the facts straight.

The big variable that would influence this is the length of the moment arm, r.


If you're talking about the length of a lever arm (r) which is the magnitude of a lever arm vector (r) then this is slightly different to the position vector of a particle (r too). Anyway, I assume you mean that the big variable is the position of the centre of gravity. Perhaps you are starting to realise why this variable is of interest to certain people.

If it were "top heavy", or if it had been hit much lower, and the arm were longer, the angular momentum would be larger, and it might have reached an overturning moment that would have carried more of top out over the edge.


You may remember me saying that the point of impact was part of the equation. This affects the size of the top section, which affects the position of the centre of mass. It also affects the total mass of the section, which in itself affects the total momentum. And the greater the momentum the harder it is to stop.

The north tower also tilted somewhat as the collapse started, but since there was a much smaller section, the angular momentum was not as large.


Absolutely. Less mass generally means less momentum.

But my pal does not have any ideas brewing in regard to WTC1 so I'm not too concerned about that at the sec.

So anyway, I am a bit more impressed with how you have come across this time. For starters you have not called me any dirty names. Calling me a no-planer is just going to rub me up the wrong way. You probably don't quite realise how much.

Hopefully we are past that now.

Shall we kiss and make up?

[sylvan8798]

Since you believe that I have no idea what I'm talking about, there is no point to furthering this conversation.

[newton3376]

I couldn't get over this exchange....

You have proved my point... it ain't just truthers who are muddled.

The planet you live on has angular momentum. It is rotating. But it is not rotating around some solid axle to which it is attached. It is rotating around its CENTRE OF MASS. And this is because it is not attached to ANYTHING. Now how much steel and concrete do you think it would take to instantly stop it from spinning? You think it will stop as soon as it hits something regardless how how much energy this something is able to absorb before it gives way? You and I must be living on different planets altogether.

I was referring to the TOP OF THE TOWER. Now you are talking about the planet. Way to stay on topic. Where do YOU think it was rotating about?

The reply to the last post be sylvan is just classic....the awesome parts are bolded...

It is exactly the same thing. They are both massive bodies with angular momentum. They are not attached to anything.

:lolsign:

The WTC and the earth are the exact same thing...

Apparently we can add THE EARTH to the list of objects (like cardboard and fruit) that we can use as analogies for various aspects of the WTC.....

INCREDIBLE! :)

[r2d2m2]

:lolsign:

The WTC and the earth are the exact same thing...

Apparently we can add THE EARTH to the list of objects (like cardboard and fruit) that we can use as analogies for various aspects of the WTC.....

INCREDIBLE! :)

No. The WTC and the earth are not the exact same thing. You are twisting my words so that you can ridicule me. Surely there is a better way to raise your self-esteem?

[newton3376]

no. The wtc and the earth are not the exact same thing. You are twisting my words so that you can ridicule me. Surely there is a better way to raise your self-esteem?

fail

[Gravy]

New Yorkers need to count their lucky stars. If WTC2 had been a bit more substantial the destruction could have been much greater.Um, if the structures had been more substantial, they might not have collapsed.

Did those links I gave you help you to understand why the top of the south tower didn't fall intact into the street?

Sincerely,
A New Yorker

[sylvan8798]

Um, if the structures had been more substantial, they might not have collapsed.

Did those links I gave you help you to understand why the top of the south tower didn't fall intact into the street?

Sincerely,
A New Yorker

Perhaps r2 has gone off to consult with Goldstein's Classical Mechanics before climbing any further out on that limb...:boggled:

http://www.amazon.com/Classical-Mechanics-3rd-Herbert-Goldstein/dp/0201657023/ref=sr_1_2?ie=UTF8&s=books&qid=1248232643&sr=1-2

[r2d2m2]

Um, if the structures had been more substantial, they might not have collapsed.


I totally agree. There are many possibilities. There is a bit more substantial. There is a lot more substantial. There is a bit less substantial. And so on. It could have been less destructive. It could have been more destructive.

That is what I'm getting at with the lucky stars. The collapse was by no means guaranteed to go one way or the other. The idea that the top section could not have possibly tipped more than a few degrees does not rest well with me. And I don't like the idea that it definitely should have done either. For exactly the same reasons.

Did those links I gave you help you to understand why the top of the south tower didn't fall intact into the street?


Well I had a look at a couple but they didn't really improve my understanding of that fact. This relates to what I just said about the lucky stars. In my opinion some of the current explanations need improvement. The way I point this out may give some people the impression that I'm a truther but they have me all wrong. I just don't like amateur debunking that's all.

"A simple graphic explanation of why the top of the south tower didn't fall to the side" is a prime example. It doesn't even account for the dimensions of the upper section for a start. I could go on. A truther would for sure. And it would not take him long to convince 5000 followers that they shalt not pay any attention to "duhbunkers".

And as for the intactness bit I certainly don't need any explanations. I can picture the top section falling apart all by itself once it's moving through the atmosphere at a rapid rate of knots [reactive force-user's in-joke]. I can almost see another weird and wonderful force by visualising its effect on an elasticated, rotating building [centrifugal force-user's in-joke]. In my book the top does not need to crash into anything in order to break up. It all depends what kind of forces it can handle. Angular momentum is significant in this respect because with breaking up you get scattering.

Having said that, I really must reiterate... This is not what I was interested in in anyway. People have just assumed that this was my concern because of the question I asked. Yet when I originally asked my question this matter had not even crossed my mind.

I am dealing with a somewhat different truther argument. Possible new. Possible coming to a home cinema near you later in the year. I am on the case of the mysterious loss of angular momentum and I am still piecing it together. This is nothing to do with any tipping before the collapse or any going sideways. It is to do with the rotation of the top section as it comes down (directly or otherwise).

Maybe you didn't get my earlier joke about the COM frame and the zeroeth law.

Personally I suspect that whoever has detected suspicious patterns in the angular motions of WTC2 is in need of a magnifying glass. They are missing a few important details. But we shall see.

Sincerely,
A New Yorker


That's one reason I have to love you Gravy. I've got a great big soft spot for the King of New York as well as many other top men from the Big Apple. In fact if there's ever a Battle of New York you might even see me there (defending the Brook with Papoose).

You also remind me of a line from one of my favourite musical creations...

"...And splatter your gallbladder, my mathematical data, travels far beyond the stars of William Shatner, Their rattling can't deport all my speed of thought, that escapes from New York and reach London on import..." Gravediggaz - Pit Of Snakes [The Pick, The Sickle And The Shovel]

I may be leaving this forum soon Gravy. Take care of yourself.

[Gravy]

Well I had a look at a couple but they didn't really improve my understanding of that fact.
OK, you had a look at a "couple" of the six links I gave you. Since they are directly related to your subject of interest, why not take a few minutes to view them all?

Well, perhaps you encountered the answer to this question, which is given in those links: according to a world-renowned structural engineer, at approximately what degree from the vertical would the WTC tower columns in the impact zones – as built – have failed?


That's one reason I have to love you Gravy. I've got a great big soft spot for the King of New York as well as many other top men from the Big Apple. In fact if there's ever a Battle of New York you might even see me there (defending the Brook with Papoose).

You also remind me of a line from one of my favourite musical creations...

"...And splatter your gallbladder, my mathematical data, travels far beyond the stars of William Shatner, Their rattling can't deport all my speed of thought, that escapes from New York and reach London on import..." Gravediggaz - Pit Of Snakes [The Pick, The Sickle And The Shovel]

I may be leaving this forum soon Gravy. Take care of yourself.Um, WTF?

[FineWine]

.
Actually, NO!

Now this demonstrates how good the information is and how well it has been distributed in nearly EIGHT YEARS.

Go to Lon Waters' site to see the cross sections of the columns over the height of the towers.

http://wtcmodel.wikidot.com/system:list-all-pages

I think it is impossible to make a top heavy skyscraper stand and withstand the wind. I have been demanding a table specifying the TONS of STEEL and TONS of CONCRETE on every level since the cows went home. Some people here say it is irrelevant.

There were more than 2500 exterior wall panels on each tower. the NCSTAR1 report says 12 different grades of panel were used but they do not tell us the quantity and weight of each type. An article fron an engineering magazine in 1970 says the heaviest type was 22 tons but that is all the information I have encountered about it.

We don't have information on the weight of the beams connecting the core columns either so this entire business is an idiotic mess. We are waiting for Ryan Mackey to build us a scaled model. But I think the distribution of mass had to significantly affect the outcome.

http://www.youtube.com/watch?v=z0kUICwO93Q

http://www.youtube.com/watch?v=LXAerZUw4Wc

psik


Will you ever tell us why the real engineers are wrong about your obsession? Will you ever explain how you know more than people who have studied engineering for years? You pretend that you have been "demanding" the insignificant information that you have often been told how to find. To whom do you make these "demands"?