9/11 Physics from Non-Experts

[gumboot]

Correct and constant motion denotes nO external force. For example, say you go outsomewhere in space and you shoot a bullet with a muzzle velocity of say 3000 fps. If no outside force acts upon it, it will still be going 3000 fps in a year, decade, century and so on. Constant motion is a sign of no external force. Why do some people have such a hard time grasping that?

That's not entirely true. Constant motion can also be a result of external forces in equilibrium, just as a static position can also be a result of external forces in equilibrium.

for example when an object is sitting on the ground, not moving, but there are indeed forces acting on it - gravity and normal force.

It is accurate to say that an absence of external forces will mean zero change in momentum, however it is not accurate to claim, therefore, that zero change in momentum means no external forces.

This is a logical fallacy, called affirming the consequent.

I think what you mean is the net force is zero.

If there is no external force, net force is zero.

However if net force is zero that does not necessarily means there is no external force.

-Gumboot

 

[SYLVESTER1592]

Actually, watching the collapse, I suspect very little impact force was applied directly to the columns. I think that's one of the problems with the design that resulted in such a catastrophic collapse.

By nature of gravity, most of the collapsing mass fell inside the building's footprint (it had to). This means it was inside the exterior columns. We can see evidence of this in the fact that the exterior columns peel outwards as the collapse occurs. That means, immediately, half the mass-supporting structure is removed from the equation.

That leaves the core columns, but as we know the building twisted as it fell. That makes it highly unlikely that the core columns lined up.

Instead, the force of collapse was left on the light weight truss systems.

Designers of the WTC talked about aircraft impacts being like a pencil pushed through a mosquito net. I think that's a good analogy for what happened in the collapse. The lower core columns would easily punch through the floor trusses in the upper section, and the upper core columns would easily punch through the floor trusses in the lower section.

Consider the below very simplified collapse model
In this model, what is actually taking the force of the collapse? The columns?

-Gumboot

Nice model. Simple and effective if you keep it's limitations in mind.


I imagine that would also help to explain why the top floors were destroyed so quickly during the collapse, as the central column would spear through the connections between the top floors and the columns as the top fell, increasing the asymmetry of the load. The top floors would have been destroyed at a distance about 14 and 24 floors down from the top...yes?

It would crash down along the remaining lower structure, despite the torsion and tilt of the top. It would do so at least initially since the center of gravity of the upper structure didn't pass beyond the perimeter columns and further down because the broken columns would slide past each other at a distance, but limiting a further movement of the center of gravity of the top towards the perimeter and tearing up the floors due to the twist and tilt of the upper structure. The total weight of the top floors would bear down on the severed columns (at least in the model), resulting in the columns to punch through the floors.

I'm simplifying of course and not sure if I'm right,..
The discussion if you want to choose Wierzbicki's or Bazant's explanation for floor support failure, may be relevant here...
Need some help on that one. I would have to read the posts and the papers a few times over again.

 

[gumboot]

Nice model. Simple and effective if you keep it's limitations in mind.


I imagine that would also help to explain why the top floors were destroyed so quickly during the collapse, as the central column would spear through the connections between the top floors and the columns as the top fell, increasing the asymmetry of the load. The top floors would have been destroyed at a distance about 14 and 24 floors down from the top...yes?

It would crash down along the remaining lower structure, despite the torsion and tilt of the top. It would do so at least initially since the center of gravity of the upper structure didn't pass beyond the perimeter columns and further down because the broken columns would slide past each other at a distance, but limiting a further movement of the center of gravity of the top towards the perimeter and tearing up the floors due to the twist and tilt of the upper structure. The total weight of the top floors would bear down on the severed columns (at least in the model), resulting in the columns to punch through the floors.

Yeah, that's pretty much my thoughts.

Bear in mind that the core columns themselves are also made up of welded segments 3 stories high. In the diagram I provide they're not exposed to much compression force (relatively speaking) however the collapse would no doubt exert a lot of random lateral force against them as the buildings rip apart. As such one can expect the upper section column welds to break apart during the collapse, and probably the top of the lower section columns as well.

In an ideal situation NIST or someone else would have marked where every single column and exterior panel landed (they were all labeled). This sort of data would have been invaluable, and with it NIST might have even been able to produce a rough model of the collapse progression.

However at the time as many as 7,000 people (or more) were feared trapped in the rubble, and the priority was recovering them.

-Gumboot

 

[qarnos]

What I find interesting about all this is exactly how the truthers came to this point - trying to prove progressive/pancake collapse is impossible:

They see the "squibs". This must mean there were bombs on every floor.

Then a debunker comes along and says, "why on Earth would they put bombs on every floor - that is unnecessarily complicated."

Hmm... thinks the truther. This must mean that progressive/pancake collapse is impossible!

So now they spend their time using warped physics and the "soda can tower" to "prove" their point.

The lies just keep snowballing.

 

[Totovader]

Oh my...

Well, that's it fellow NWO members. He's "debunked the debunkers"



He's managed to figure out that if the core columns would have "buckled" (his strawman), that the entire building would have bent like a big "C"...

Absolutely amazing.

 

[westprog]

Oh my...

Well, that's it fellow NWO members. He's "debunked the debunkers"



He's managed to figure out that if the core columns would have "buckled" (his strawman), that the entire building would have bent like a big "C"...

Absolutely amazing.

Well, he's convinced me. The net force is zero, simple Newtonian physics, he's given the debunkers a fair shot at it.

What I like is the way that the voice gets higher as he hits a really dubious bit of reasoning as he needs to convince himself.

In the second half, he explains that if we treat the beams on a per floor basis, then they would have to have bowed symmetrically, and hence held up the building BECAUSE THE FORCES ARE EQUAL. He then switches to a picture showing the top of the building at a considerable angle. By then he's already forgotton the reasoning he was using before.

 

[AZCat]

Oh my...

Well, that's it fellow NWO members. He's "debunked the debunkers"



He's managed to figure out that if the core columns would have "buckled" (his strawman), that the entire building would have bent like a big "C"...

Absolutely amazing.

His strawman is breathtaking in its stupidity. Who ever argued that the buildings would fail like that (at least, who in their right mind)?

 

[gumboot]

I love where he says and alternative reaction from the building if the core columns shattered was that the building would start to collapse from the bottom.

So basically he's saying it has to be a controlled demolition, because if it wasn't a controlled demolition, it would look like one.

Un-[rule8]-ing Believable.

-Gumboot

 

[Totovader]

If you notice- he does debunk himself, however. He admits that he's not saying the building wouldn't fall- as he tries to move the goalpost to regress his argument to the "net force is zero" claim- and claim that you can't argue with Newtonian Physics (and coincidentally, anyone who does is a fool). He claims that people are using strawmans against him when they claim that he is asserting the building wouldn't fall. Never mind that this has been his clearly stated position the whole time.

That's a sign that he's figured out his error. Of course- he just dives right back into it. Every other statement he's made completely contradicts this; his next statement about the explosives in the upper part of the building "as it's falling" expose his position as being a bit more than just "the net force is zero".

I know he reads this- and since he's blocked everyone who disagrees with him: You can't have it both ways, bud. You cannot claim on the one hand that you aren't making any specific statements about the collapse, and then turn around and make very specific statements about the collapse. You're debunking yourself.

 

[Horatius]

But at least he gave a shout-out to the JREF forum!

So once again, a twoofer is inadvertently pointing people to a good place to learn some actual physics.

And it's nice to see, that in "acknowledging" that the buildings had structure, he manages to forget that the core columns were also a complex structure. There's simply no way they could have buckled along their whole length like he shows, as they would have snapped at the weld points along the length. And of course, his claim that that's the model we're promoting is a pure strawman.

Not to mention, his concept that they should have buckled at the "point of maximum leverage" ignores the structure of the floor trusses, which were designed to prevent just exactly that sort of buckling.


The really sad part is, with his "buckling of each floor" argument, he's almost got it right. Yes, each floor would fail in series. Yes, each floor would absorb some energy in doing so. The problem is, he asserts, without any proof or analysis, that such absorbtion would be enough to stop the upper block. And that's where he loses it.

You simply cannot make that assertion without some supporting calculations. Stick figures on a video don't count. He says he knows physics so well, so lets see the math. Without actual math, he's just blowing smoke (and actually hand-waving, nice touch).

We've got papers that show such calculations, and they show he's wrong. so where is his math?

He's also made the claim that "his only claim" is that the upper block could not have accelerated, as the net force is zero. Well, the net force wasn't zero. If he claims it was, he needs to do a lot more than draw pictures and wave his hands to show that.

Oh, but there I go again, misusing my freedom! Bad, bad JREFer!

 

[JamesB]

This guy is hilarious. That is one of the funniest things I have seen in a while. They don't understand how entertaining they are as parodies of themselves.

 

[SYLVESTER1592]

What I find interesting about all this is exactly how the truthers came to this point - trying to prove progressive/pancake collapse is impossible:

They see the "squibs". This must mean there were bombs on every floor.

Then a debunker comes along and says, "why on Earth would they put bombs on every floor - that is unnecessarily complicated."

Hmm... thinks the truther. This must mean that progressive/pancake collapse is impossible!

So now they spend their time using warped physics and the "soda can tower" to "prove" their point.

The lies just keep snowballing.

NIST NCSTARCollapseofTowers Ch 5.3.6 p63 describes a smoke purge system that stretched over several floors. NIST NCSTAR 1-5 Chap 1.1 p57 describes how the ventilation system was damaged and explained how smoke could travel, but it was not fully modeled.
NIST NCSTAR 1-5 Chap 4.2 description of the fire dynamics simulator p124 describes the boundaries for the model. Here they mention the presence of HVAC air-conditioning and ventilation ducts. I would expect the traveling debris and dust cloud to be funneled through these ducts. Dust in these ducts would travel at a higher velocity then the debris and dust cloud that pressurized it, much like a bicycle pump...

NIST NCSTARCollapseofTowers Ch 8.5.3 Fire Safety, explains that there was no "fire tower" (staircase with natural ventilation) so that would basically exclude the staircases as a funnel for the debris regarded as "squibs"
Exiting the building, I guess the dust from these ducts could have been mistaken for "squibs".

It's not easy to find a plan which shows the exact layout of the ducts. The Port authority probably has them, but I think the statement that "there is no other explanation then explosives" can be refuted.

The "soda can tower", actually does buckle inward and twists as it crushes. There are however two main problems: they don't weigh much and carry a very large load (compared to their own weight). Most people don't realize that the towers were built to withstand forces that were relatively small compared to the support of the structure itself. When the tower itself started to collapse, the force distribution and energy of the collapse far exceeded any purpose of the buildings design. People think you try to fool them by presenting a rickety structure, when in reality you show them a structure that is mainly concerned with maintaining it's own integrity in the presence of relatively small external forces. It's very hard to present an analogy that will explain that convincingly to someone using only "common sense". Of course there are people that just don't want to understand.

I'm not defending it, but I understand the mistake...and the frustration it evokes.

 

[westprog]

He's also made the claim that "his only claim" is that the upper block could not have accelerated, as the net force is zero. Well, the net force wasn't zero. If he claims it was, he needs to do a lot more than draw pictures and wave his hands to show that.

He's plainly shown that the net force was zero, because if it wasn't zero, the building would be collapsing. The building couldn't be collapsing because the Net Force Was Zero. IT'S SIMPLE ***ING NEWTONIAN PHYSICS!

At least in the sense that his arguments are in a simple orbit. I think he's using his conclusions to prove his assumptions, but the reasoning is so unclear that it's very difficult to see what he's getting at. It's obviously very, very wrong, but getting a clear argument that can be dismissed isn't easy.

 

[jaydeehess]

Actually, watching the collapse, I suspect very little impact force was applied directly to the columns. I think that's one of the problems with the design that resulted in such a catastrophic collapse.

By nature of gravity, most of the collapsing mass fell inside the building's footprint (it had to). This means it was inside the exterior columns. We can see evidence of this in the fact that the exterior columns peel outwards as the collapse occurs. That means, immediately, half the mass-supporting structure is removed from the equation.

That leaves the core columns, but as we know the building twisted as it fell. That makes it highly unlikely that the core columns lined up.

Instead, the force of collapse was left on the light weight truss systems.

Designers of the WTC talked about aircraft impacts being like a pencil pushed through a mosquito net. I think that's a good analogy for what happened in the collapse. The lower core columns would easily punch through the floor trusses in the upper section, and the upper core columns would easily punch through the floor trusses in the lower section.

Consider the below very simplified collapse model:

[qimg]http://www.internationalskeptics.com/forums/imagehosting/10153463ffade65489.jpg[/qimg]

In this model, what is actually taking the force of the collapse? The columns?

-Gumboot

That is actually more along the lines of what I could envision occured as well.
It adds to my idea that the peeling away of the perimeter columns was a result of the mass falling through and filling up the space between the perimeter columns. Pour sand into a milk carton and the sides bulge outward indicating an outward force. Dump that sand in very quickly and the force on the sides increases, have it enter that carton fast enough and the seam of the carton will fail. As the upper section fell, all that debris would still be falling into the space between the perimeter columns at great velocity, filling the floors and exerting an outward force on the perimeter column trees.

That outward force is the result of the downward movement of the debris being slowed by the resistance of the floors. As the floors offered some resistance to the falling debris that debris piled up inside the perimeter, this forces the perimeter columns outward, once the impulse force and gravitational force of the mass fails the floor(this would happen very quickly since the floors were designed to transfer only the load of the mass of the objects on each floor , not a significant percentage of the mass of the entire building) that severs the lateral support on the perimeter trees which are then ejected outward.


I note that the twoof expected that the upper section would topple over to one side. I would ask him what force would be present that would cause the upper section to select a preferred direction to fall. In his drawings he has that the initial collapse would be assymetrical and indeed it would but he expects that the higher side of the lower section would act as a pivot point and cause the upper section to rotate, or he expects that it would result in an inclined plane that would see the upper section slide off.

In the firstcase, the upper section toppling over, the force on the pivot would very quickly crush it once again resulting in a more vertical fall. Now that the upper section is no longer pivoting, the rotation occurs about its ceter of mass rather than the pivot point. Unless that center of mass gets beyond the perimeter of the building the bulk of the mass of the upper section IS STILL falling inside the perimeter columns!

In the second case, the upper section sliding along an inclined plane, this is patently ridiculous. As soon as the columns do not line up they fall through the space between columns. Even that assumes that the columns could slide apart at all. More likely they are buckling and all they need do is buckle to a point where they can no longer resist the vertical force on them and they will then shear off at the buckled section once again resulting in a vertical fall.

 

[jaydeehess]

At the time of collapse initiation the coulmns could no longer 'push back' enough to support the load. Thus at that time the net force is NOT zero and thus the uppersection begins it downward movement as a result of that imbalance. It gains momentum in this way. If the lower section can arrest all of this momentum then the upper section will only offer the force due to its mass on whatever it is resting upon(which as pointed out above, is unlikely to be the columns). If it could not arrest all of that momentum then it would still have some velocity from its initial fall and that would add to any increase in velocity as it fell through the collapsed next floor space which would mean that it contained greater momentum than it did in the initial collapse. If the first impact after initial collapse could not arrest that value of momentum and the upper section had not shed enough mass to make its momentum smaller than at the first impact, then the next floor can hardly be expected to arrest a greater momentum than the first impact.

That momentum is absorbed over the time of each impact and the distance it travels during that time. This gives the us energy absorbed (IIRC). The energy the floors can absorb is basically fixed but the energy available due to the falling mass goes up in proportion to the square of the velocity even though the momentum is only directly proportional to velocity.

 

[gumboot]

It's funny; the CTers like to talk about the "massive" core columns. I think part of the problem is, they have no understand of what "massive" in building terms means.

In the area around the collapse zones, the very largest core columns were about 0.55m square. Even assuming all 47 core columns were of the box-weld shape (they weren't) and all of the largest size (they weren't), and solid steel (they weren't) you're only talking a cross section (combined) that's 14.2m², or 0.35% of a given floor's total area.

Even if you add the 240 exterior columns (0.355m x 0.355m) and assume they are solid (again, they weren't) you still get less than 45m² of total column cross section, or 1.1% of the floor's total surface area.

This is why enormous buildings can stand, but when something is taken out of whack the result is catastrophic. It's a careful balancing act.

I recall once someone said if superman tried to catch the falling towers in midair by grabbing hold of one core column, it would simply rip the building apart and the thing would keep falling down, with superman left sheepishly holding a single piece of column.

Even if the upper mass perfectly landed on the core columns somehow, a similar thing would have happened. The exterior columns were undermined by the failure, and the core columns cannot hold the building on their own. The floor trusses and exterior columns of the upper mass would have ripped free of the core columns, and smashed through the bottom of the tower with the same result we saw on 9/11.

As it turns out, the building had to only shift half a meter in any direction, and those columns would no longer line up.

I think the exterior column idea, with no internal spaced columns, was part of the fatal design for the WTC, given a collapse scenario.

Essentially, the structural integrity of the entire structure ended up relying on the very weakest element in its entire structure - the fixtures that held the floor trusses to the core columns and exterior column spandrel plates.

Far as I can tell, each truss was connected to a thin ledge on the spandrel and bolted in place. On the interior the truss was attached to the frame, with bolts attaching to channels welded to each core column.

In all, with exterior fixtures on every second column, that's 116 exterior fixture points and 26 interior fixture points. And that's it.

The irony is, of course, the collapse was initiated because those exact some fixture points in the impact zone didn't fail.

So the floor truss connections twice-doomed the towers.

-Gumboot

 

[jaydeehess]

The irony is, of course, the collapse was initiated because those exact some fixture points in the impact zone didn't fail.

So the floor truss connections twice-doomed the towers

Interesting take on that. The truss seats do not fail under the stress of the sagging floors thus allowing that stress to bow in the perimeter columns which themselves fail and which then would have required that the floor truss seats on the next intact floor be able to take the weight and impact of the upper section in order to halt collapse.

how's physics boy holding up to his critics?

 

[beachnut]

Oh my...

Well, that's it fellow NWO members. He's "debunked the debunkers"



He's managed to figure out that if the core columns would have "buckled" (his strawman), that the entire building would have bent like a big "C"...

Absolutely amazing.

Is he trying to be nuts? He actually debunked himself a few times.

Do his followers know his physics is out to lunch? Are they all dropouts?

OMG, there is a whole nest of people who are supporting the new UTube physics fraud. Cool. How do people get to be so challenged and unable to understand physics, or take the time to gather knowledge. The UTube physics teacher is funny, his Sam Kinison routine at the end is GREAT. I wish he would just do the physics rant he does at the end for a whole tape, like Sam would do.

 

[Vincent Vega]

Its the case of "a little information making one dangerous". The one thing that truthers have in common is their missunderstanding of the energy and forces involved.

I've tried to explain that energy is energy whether it is chemical or kinetic. And the energy involved in moving masses as large as the WTC are just not applicable to everyday experiences, which is where most "Woo-Fiziks"
originates from...beter known as "common sense".

 

[Totovader]

<snip>

how's physics boy holding up to his critics?

What critics?

He just blocks them all and removes their comments. Problem solved.