The 9/11 Forum

If the block is dropped it is not going to turn to dust after falling 200 feet. It will remain perfectly intact until it hits the ground. So how did the supposed PE of the WTC produce dust hundreds of feet above the ground?

Things collided before hitting the ground. It's in your simulator. Inelastic collisions, huge energy sink. Inelastic means deformation, crushing.

OneWhiteEye wrote:Things collided before hitting the ground.

Most definitely, yet that is ignored when one abstracts the situation into to calculating PE as if describing a ball dangling from a rope.

Pavlovian Dogcatcher wrote:

OneWhiteEye wrote:Things collided before hitting the ground.

Most definitely, yet that is ignored when one abstracts the situation into to calculating PE as if describing a ball dangling from a rope.

No, it's not ignored. I explained it above, again. For the ?th time. It is NOT described as a ball dangling from a rope. It's described as a mass supported statically until that condition is no longer true. Any PE change resulting from elevation loss goes into work to deform material and what's left over is the energy of motion, kinetic energy. If there's very little left over for KE, the mass descends slowly, if a lot then quickly. The PE change is same in either case and is given by the mass and the change in elevation.

Make sense?

OneWhiteEye wrote:

Pavlovian Dogcatcher wrote:

OneWhiteEye wrote:Things collided before hitting the ground.

Most definitely, yet that is ignored when one abstracts the situation into to calculating PE as if describing a ball dangling from a rope.

No, it's not ignored.

It's ignored when done as I said, and that is how I've seen it done to varying extents in attempts which I've dismissed on those grounds. Please show me whatever you believe to be the best example to the contrary.

psikeyhackr's simulator.

Edit: Let me make it plain. I've never seen it (collision energy) "ignored when one abstracts the situation into to calculating PE." As I say below, calculations for step-wise model collisions do not even involve PE. Please provide at least one example which supports your claim.

Any computational simulation which has inelastic collisions takes into account the energy lost to collisions. That aspect has nothing to do with PE, the PE doesn't change in a idealized, instantaneous slab collision. psikeyhackr's simulator has magic supports that go away at collision, but the collision takes place and dissipates kinetic energy. That energy goes into crushing, so even without fail energy, his simulator expends energy for concrete comminution, in mid air. Once supports are added, these will become an additional sink which will act to retard downward motion further.

To the extent that a ball dangling from a rope is supported statically, it is no different than the situation while the upper block is supported statically. The progressive loss of support capacity for initiation is also similar - creep from temperature / frayed rope - both reaching maximum capacity and failing. Difference then is, ball has nothing underneath it but every simulation or computation I've seen has successive impacts.

Both of you keep missing the idea that the change of potential energy is incremental, as it drops, however far it drops. You don't invoke the entire PE of the building relative to ground level to get it going! You decrease the capacity (a force) through degradation over time, until the support force is less than the load. This results in PE loss, KE gain. Only for that level, then the collision and (full capacity) support resistance come into play at the next level, and so on.

Pavlovian Dogcatcher, do you understand the relationship between force and work done by a force?

OneWhiteEye wrote:As I say below, calculations for step-wise model collisions do not even involve PE.

You were talking about calculations of PE here:

OneWhiteEye wrote:Any PE change resulting from elevation loss goes into work to deform material and what's left over is the energy of motion, kinetic energy. If there's very little left over for KE, the mass descends slowly, if a lot then quickly. The PE change is same in either case and is given by the mass and the change in elevation.

Anyway, sure Psikeyhackr's simulator effectively accounts for what you describe, but have you seen any attempts to calculate "the PE of the towers" which rightly do?

OneWhiteEye wrote:Please provide at least one example which supports your claim.

See appendix B here, where the mass of a tower and it's center of mass are estimated to supposedly calculate the PE of the tower by abstracting it into a ball suspended from that height; resulting in the value of 4.09 x 10^11 Joules. Comically, such calculations are further used to argue:

This is a vast amount of energy, and compares well with the estimated energy needed to destroy the columns on every single lower floor. This result also proves that, in order to significantly accelerate the collapse process, Dr. Griffin’s hypothesis calls for many, many tons of high explosives, much more than could possibly be placed or detonated covertly.

Of course that argument is nothing more than a false dichotomy; absurdly suggesting gravity doesn't remain in effect once explosives are used.

As for your question on the relationship between force and work done by a force; best I can tell, I understand it far better than you do.

Pavlovian Dogcatcher wrote:

OneWhiteEye wrote:As I say below, calculations for step-wise model collisions do not even involve PE.

You were talking about calculations of PE here:

I was talking about PE but I wasn't talking about collisions! I then separately answered psikeyhackr's question which concerned collisions, but not loss of PE except that's why the collision occurs in the first place:

OneWhiteEye wrote:Things collided before hitting the ground.

You brought collisions and PE together:

Pavlovian Dogcatcher wrote:Most definitely, yet that is ignored when one abstracts the situation into to calculating PE as if describing a ball dangling from a rope.

See below.

Anyway, sure Psikeyhackr's simulator effectively accounts for what you describe, but have you seen any attempts to calculate "the PE of the towers" which rightly do?

Mine, Greening's, femr2's and others - that's why they all pretty much agree with psikeyhackr's calculations. Mackey's analysis ignores collisions specifically but is nonetheless correct within the scope of what he attempts to do.

See appendix B here, where the mass of a tower and it's center of mass are estimated to supposedly calculate the PE of the tower by abstracting it into a ball suspended from that height; resulting in the value of 4.09 x 10^11 Joules.

Point to you for finding such an analysis, but that's all you get. I never read his paper, so I didn't know he did this and it's the first time I've seen such a calculation simply involving total energy budget over the entire collapse. Nonetheless, the analysis appears correct, and the method most certainly is. While inelastic collision is not called out, nothing specific is - all known and unknown energy sinks are rolled into one big sink, which INCLUDES collisions.

He does a 'what if' table calculating how the overall collapse time differs when kinetic energy (gained from PE loss) is diminished due to loss to any and all sinks. Momentum-only collision is near the top of the list, probably between 39% and 48% dissipation fraction. Add more sinks if you like, it just goes lower in the table and longer on the collapse time.

There are continuum models, step-wise discrete models, and there is an aggregate calculation like what Mackey did. It's only step-wise if you consider one step to be a step-wise calculation. It doesn't specify motion over time, just total time and is appropriate only for that. Mackey's one step has boundary conditions at the beginning and end of collapse, story-wise computations like mine are just that, by story. femr2 and psikeyhackr both use timesteps, not story steps. Mackey cannot accurately test for arrest, he can only say what the net energy dissipated by the structure is if it collapses to completion and show the times for fraction dissipated. Even his model 'arrests' when the total dissipation equals total PE lost, the only case in which it will.

You assume because collision is not mentioned in Mackey's paper that energy lost to it is overlooked in the calculations, which is not so. It's not necessary to specify what the energy goes towards to calculate collapse time from net energy balance.

As for your question on the relationship between force and work done by a force; best I can tell, I understand it far better than you do.

Your response dodges giving the answer to a very simple question, so I don't think so. There's still the opportunity to go find a wiki page to link to, and copy and paste.

The answer to my question, with application, is found in appendix B of Mackey's paper! Don't even need to go to Wikipedia. Quite amusing.

He is in no position to draw this conclusion. Suppose, for instance, the structure – even
damaged and during collapse – was capable of supporting twice the static load, which we
will call Fstatic, but that it could only do so until being deflected by 25 cm. After this, any
given floor will snap, and the resistance goes to zero until the next floor is hit 300 cm
below. Work, again, is force times distance. The total work done on any given floor
would be 2 Fstatic x 25 cm + 0 x 300 cm = 50 Fstatic cm. If we model the structure as
homogeneous, supplying instead an average force called Fdynamic that acts over the full
325 cm distance of each floor, we can estimate this average force by dividing the total
work by the total distance. The total work done in both situations must be the same.
Therefore, we can calculate Fdynamic = 50 Fstatic cm / 325 cm = 0.15 Fstatic, what Dr.
Kurttila would call a “resistance factor” of 0.15, very close to his estimate for WTC 7.

Emphasis mine.

This is about the same run down I was going to give psikeyhackr.

Failure to understand the bolded portion above seems to be at the root of much misconception regarding progressive collapse.

It plays a large role in this gentleman's misunderstandings, and figures prominently in David Chandler's 3rd law argument.

OneWhiteEye wrote:

...have you seen any attempts to calculate "the PE of the towers" which rightly do?

Mine, Greening's, femr2's and others...

Please present whichever one you believe is best, so I can address it directly.

OneWhiteEye wrote:Your response dodges giving the answer to a very simple question...

Rather, you asked "do you understand...", and answered your question directly by noting the fact that I do.

Pavlovian Dogcatcher wrote:Please present whichever one you believe is best, so I can address it directly.

Apples, oranges and plums. femr2's spreadsheet is here:

http://the911forum.freeforums.org/wtccs-spreadsheet-crush-down-model-t159.html

Greening's model is here, no program or spreadsheet:

http://www.911myths.com/WTCREPORT.pdf

Mine you have to wait for documentation, or ask questions about. Or you can look at the toy simulacra thread for a different one.

OneWhiteEye wrote:Rather, you asked "do you understand...", and answered your question directly by noting the fact that I do.

Ok, ok, please tell me what the relation is.

OneWhiteEye wrote:Apples, oranges and plums.

Well, as long as you don't care to pick one to discuss specifically, I won't bother addressing any of them.

OneWhiteEye wrote:Ok, ok, please tell me what the relation is.

My interest here is in discussing Psykey's question of "how did the supposed PE of the WTC produce dust hundreds of feet above the ground?", not jumping though hoops held out by those who have an aversion to addressing that question.

Pavlovian Dogcatcher wrote:Well, as long as you don't care to pick one to discuss specifically, I won't bother addressing any of them.

That's absurd. Greening's is the best documented. Say something about that.

My interest here is in discussing Psykey's question of "how did the supposed PE of the WTC produce dust hundreds of feet above the ground?"...

Collisions, as I said above. How you can say I have an aversion to answering a question I already answered? Can things get any sillier than this? But, you, on the other hand, have been asked point blank several times to answer a question which would be trivial for anyone qualified to comment on this subject.

...not jumping though hoops held out by those who have an aversion to addressing that question.

It's not a hoop, it's fundamental to understanding the mechanics. Anyone who doesn't understand it should surely be quiet while the subject is being discussed. Sure you aren't dodging the question? I gave you the answer above, how hard can it be to regurgitate it?