Falling objects can be faster than free fall

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Basic principles of engineering (for example, the conservation of momentum principle) would dictate that the undamaged steel structure below the collapse zone would, at the very least, resist and slow the downward movement of the stories above….

[F]ree fall is not consistent with any natural scenario involving weakening, buckling, or crushing because in any such a scenario there would be large forces of interaction with the under- lying structure that would have slowed the fall.... Natural collapse resulting in free fall is simply not plausible....”

In short, incredulity, paired with the mistaken assumption that free-fall acceleration implies free fall—the ladder video shows it does not.

Since my video above evokes the same feeling of incredulity, I hope it works as antidote.

I have never been able to wrap my head around this "free-fall" argument either.

Even if you use explosives to demolish a building, you are not going to remove all resistance, unless you demolish it by vaporising the entire structure of the building, leaving the roof to fall to the ground unimpeded.

In a controlled demolition, you knock out strategic points of the structure to initiate the collapse, but that doesn't mean that the falling building is suddenly magically free of resistance.

I think there's a fundamental disconnect in this line of thinking that no video can ever bridge.
 
It has no context. That's true.

But I did not say it is out of context, which typically means it's misleading. Because the context is not provided, I can't check if it's used out of context. ae911 sometimes do that.
 
I have never been able to wrap my head around this "free-fall" argument either.

Even if you use explosives to demolish a building, you are not going to remove all resistance, unless you demolish it by vaporising the entire structure of the building, leaving the roof to fall to the ground unimpeded.

In a controlled demolition, you knock out strategic points of the structure to initiate the collapse, but that doesn't mean that the falling building is suddenly magically free of resistance.

I think there's a fundamental disconnect in this line of thinking that no video can ever bridge.

But... It was in free fall. It's measured. It's in the NIST report. So is your position that CD wouldn't cause free fall, but office fires plausibly could?

And before Oystein or someone says anything, okay, let's say it's not the entire building in free fall. Let's say it's just part of the north wall. Well, how do you get that part to drop at 9.8 m/s^2? Unless I'm mistaken, the perimeter wall had steel columns all around. There's support, there's resistance. Or there should be, but there wasn't.
 
This is a montage of 240 slices, each 4x1080 pixels, from the yt vid linked to above (id=aBYoKEbIIBg) taken from column x=800 (thus showing a bit of both foreground buildings), and restricted to the middle collapsy bit of the video:
WTC7.png

from: http://fatphil.org/tmp/WTC7.png (no promise to keep that longer than a couple of whenever-I-clean-up-the-tmp-area periods, which is unpredicable)
I made it using the following commandline utilities:
Code:
ffmpeg -i ../WTC7.mp4 -ss 9 -t 8 -vf crop=4:1080:800:0 out%03d.png
gm montage +frame +shadow +label -tile 240x1 -geometry 4x1080+0+0 out*.png WTC7.png

That ain't a parabola to my eye (it's more obvious when you do 8-pixel wide slices, but that's of course twice as wide).
 
But... It was in free fall.
No it wasn't. And the reason has been explained many times.
It was measured as Free Fall ACCELERATION. And the measurement methods were crude.
BUT most members who, like me, comprehend the physics principles, have many times AGREED it was near enough to FFA for purposes of these discussions.

It's measured. It's in the NIST report.
YES - because NIST put more information into the report AFTER the draft report was "put out for public comment" AND D Chandler asked for more detailed information. << ALSO known fact.
So is your position that CD wouldn't cause free fall, but office fires plausibly could?
That is NOT the point of contention. It is actually the status of debate by the protocols of the scientific method. (EDIT - before I get called. ;) "CD did not cause collapse - fires did".)There are many published/posted explanations of how fire caused the collapses. There has NEVER been a valid hypothesis that "proves" (i.e. legitimately hypothesises) that (a) CD Help was needed or (b) CD was performed. In fact no "truther has ever (c) postulated a valid hypothesis as to how the observed collapses (any of the three) could have been achieved by use of CD.
And before Oystein or someone says anything, okay, let's say it's not the entire building in free fall.
Pre-emptively denying opponents is not playing the game... ;)
Let's say it's just part of the north wall.
It was. That is well established. No need to pretend.
Well, how do you get that part to drop at 9.8 m/s^2?
IF you are serious I am prepared to explain one more time, in a suitable thread or this thread if Moderators allow.
Unless I'm mistaken, the perimeter wall had steel columns all around. There's support, there's resistance. Or there should be, but there wasn't.
You are not mistaken about the facts in this trio of sentences. Except the global claim "wasn't" >> there "wasn't much". And the explanations are relatively simple.
 
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That ain't a parabola to my eye (it's more obvious when you do 8-pixel wide slices, but that's of course twice as wide).
Good work @FatPhil but the real issue of disagreement here is in definitions and framing of questions. The reality of crudely measured Free Fall ACCELERATION at near enough to "G" is accepted.
 
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This graph is in the report:



Bottom right you'll see the number 32.196, which is the acceleration in feet,
Acceleration is already agreed upon by most of us.
and that works out to 9.813 m/s^2.
The 3 decimals are optimistic given the crude measurement techniques.

It is the claims for Free Fall that are one of the points of both misunderstanding and contention.
 
Explain why Chandler’s graph, in his careful analysis, shows about 1 second of non-freefall when the roofline starts to descend? If all supports were immediately cut/removed, then why didn’t the roofline start free fall at the onset?
To be fair, that could be an artifact of the sampling method and frequency.

Let me construct an example, where I tweek values and units a bit, just to make things numerically easy.
Let's say the video camera snaps a pic 5 times per second.
Let's say g = 10 m/s^2
Let's say descent starts at t = 1.0 s, and is actually immediately in free fall.
If the camera clip starts at 0.0 s, then it will capture that point in time at 1.0 when the descent is just beginning, with h=0 and v=0 in the interval [0.8 s;1.0 s].
In the next frame (t= 1.2 s), h is 0 - 1/2*g*t^2 = -0.5 * 10 m/s^2 * 0.04 s^2 = -0.2 m. v has averaged -0.2 m / 0.2 s = -1 m/s in the interval [1.0 s; 1.2 s]. That's a change of -1 m/s from the previous interval, when v was 0, for an apparent acceleration of -1 m/s / 0.2 s = -5 m/s^2 - half the value of g!
Another 0.2 seconds later, at t=1.4 s, h has dropped to -0.8 m, and v has gone to -0.6 m / 0.2 s = -3 m/s for a change of delta-v = -2 m/s within 0.2 s, which marks an acceleration of 10 m/s^2 - this is finally g!

So, to draw a table
t (s)h (m)v (m/s)a (m/s^2)
0000
0.2000
0.4000
0.6000
0.8000
1.0000
1.2-0.2-15
1.4-0.8-310

So it appears in this fictitious dataset that acceleration increases to g only over the course of 0.4 s.

It gets even worse if the descent starts halfway between frames, if, say, the camera's first frame is at 0.1 s, and then 0.3 s, ... 0.9 s, 1.1 s, 1.3 s:
t (s)h (m)v (m/s)a (m/s^2)
0.7000
0.9000
1.1-0.05-0.25-1.25
1.3-0.45-2.00-8.75
1.5-1.25-4.00-10.00

The problem is that v always lags behind in Chandler's simple method of just comparing height in consecutive frames. True instantaneous v is -1 m/s at t=1.1 s in my second table, not -0.25. True a is -10 m/s^2 at 1.3 s, not 8.75. Chandler's method, in short, would capture true freefall right from the beginning only after the 3rd frame that follows freefall onset.
And isn't it true (I am too lazy now to check) that Chandler didn't even go frame by frame, as that would be too noisy for him, and instead analyses every 5th or 6th frame?

The problem for all who analyse collapse videos is that true onset of descent is very difficult to capture. At a frame rate of 30/s, and if true onset is at half the time interval between two frames (1/60th of a second before and after the nearest frames), then the first frame after collapse onset, hypothetically in freefall, will find h= -5 m/s^2 * 1/60^2 s^2 = -1.3888 mm (millimeters!).
h(1 s/30 ) = 5.555 mm.
(Oh I am showing four and five relevant digits while working with g = 10 m/s^2 :D)

It is easy to miss the moment when the collapse of the roofline begins, but it is even more difficult to figure out when a = g begins.

Chandler's data is much too coarse to identify either of those moments.
 
Good work @FatPhil but the real issue of disagreement here is in definitions and framing of questions. The reality of crudely measured Free Fall ACCELERATION at near enough to "G" is accepted.
Yup, I just wanted to make it easier for other people to get their own numeric data, not needing to trust someone else's. Even if that's not from my precise image, the tools/techniques are now public. (It only takes a few seconds.)
 
But... It was in free fall.
No. Never.

Do you understand that you need to distinguish between "exhibits freefall acceleration" and "is in free fall"?
Like, you know, a drag car might accelerate at freefall acceleration while not falling at all, let alone "freely"?
That the valve of a wheel on a car that drives on a flat road, fast enough, will be at freefall acceleration downwards at a particular point on every turn of the wheel, and that you can always find a time interval >0 s in length, infinitely many different such time intervals in fact, during which the valve will average freefall acceleration in the direction of gravity - but neither the valve, nor any part of the car, is ever in any fall at all, let alone free fall?

Do you understand the previous paragraph? Do you agree that every claim I make therein is true?

Then you should know and understand that a point on the roofline of WTC7 might exhibit freefall acceleration during some suitably chosen time interval even though it is, conceivably at least, not then, nor perhaps ever, in free fall?

It's measured. It's in the NIST report.
NIST's measurement and analysis is far more nuanced than this.
So is your position that CD wouldn't cause free fall, but office fires plausibly could?
I dont think this resembles anyone's position here, not even remotely.
And before Oystein or someone says anything, okay, let's say it's not the entire building in free fall. Let's say it's just part of the north wall. Well, how do you get that part to drop at 9.8 m/s^2?
See video in opening post. That's one way.

Unless I'm mistaken, the perimeter wall had steel columns all around. There's support, there's resistance. Or there should be, but there wasn't.
You obviously are mistaken indeed:

Since the building had already been progressively collapsing for many seconds, including the recent buckling of the West core and the first non-g moments of the North roofline descent, it is most obviously clear that the North roofline had dramatically LOST that support and a lot of that resistance. How can you pretend there still is support when the thing is coming down?
That's the whole point of progressive collapse: More and more of the support is diminished or disappears.
To prove that this is possible in principle, only one example is needed. Mick's garage model is such an example.
 
Yup, I just wanted to make it easier for other people to get their own numeric data, not needing to trust someone else's. Even if that's not from my precise image, the tools/techniques are now public. (It only takes a few seconds.)
No problem. As often happens - it is endemic among engineers - people enjoy debating the details when there are over-ruling issues in the bigger picture. 'When you are up to your arse in alligators it is easy to forget that the objective was "Drain the Swamp"' ;)
 
This is a montage of 240 slices, each 4x1080 pixels, from the yt vid linked to above (id=aBYoKEbIIBg) taken from column x=800 (thus showing a bit of both foreground buildings), and restricted to the middle collapsy bit of the video:
WTC7.png

from: http://fatphil.org/tmp/WTC7.png (no promise to keep that longer than a couple of whenever-I-clean-up-the-tmp-area periods, which is unpredicable)
I made it using the following commandline utilities:
Code:
ffmpeg -i ../WTC7.mp4 -ss 9 -t 8 -vf crop=4:1080:800:0 out%03d.png
gm montage +frame +shadow +label -tile 240x1 -geometry 4x1080+0+0 out*.png WTC7.png

That ain't a parabola to my eye (it's more obvious when you do 8-pixel wide slices, but that's of course twice as wide).
I love it!

Do I interpret this correctly, The top contour is the West Penthouse, it starts dropping parabola-like at about 128 px from the left edge, disappears behind the roofline, starting a new parabola?

We can see the other stories, the tops and bottoms of rows of windows, hold a ruler to them, and roughly determine when they start to descend - and it appear to me they start earlier than I had so far seen the roofline drop. Here, i drew some amateurish lines with Paint:
WTC7 Smearograph - with lines.png


What I see there is that all the lines are not horizontal - they drop slightly from left to right starting at the left edge of the image. But the foreground buidling remains horizontal and straight. Therefore, there is downward movement much earlier.
4 pixels is 1 frame of 1/30 seconds?
This strongly suggests that buckling of the North wall columns started earlier than I thought, than perhaps many of us thought.
And that means acceleration early on was less than what Chandler measured, less perhaps than what NIST measured.

(But smarter minds with more time to spare have poured over these videos long enough. @femr2 for sure analysed early motion and found lots of it. Has anyone tracked other floors?
Some of the motion probably is not actually downward but bending inward.
 
This relates to bunk spread by members on this site and it makes me very angry. There is no evidence of over g collapse in 9-11, it is bunk we should not entertain.

This bunk keeps coming back like that old friend... I know where this goes from past experience on eventually locked threads.

It's bunk if it is false.
If it is true, but the evidence has been deleted, then it is unprovable for the time being.
Not bunk.

I do remember the same evidence that @econ41 remembers: It had been presented and linked to in a couple of fora, but one or two of those fora have gone out of existence, and the storage space linked to that contained the data and analysis has been discontinued.

So that's a shame. It means we can't, for the moment, present that data for scrutiny, and you can dismis caims of over-g at WTC out of hand.
But to claim they are bunk would require for you to falsify over-g.

There is a simple argument why over-g is at least plausible (and in my opinion probable):
All agree that there was an interval of approximately 2 seconds during which acceleration was equivalent to g. If that is true, then there are exactly two possible explanations for it - a true dilemma:
  1. Either instantaneous acceleration was exactly equal to g throughout the entire ~2 s interval
  2. Or instantaneous acceleration was not exactly equal to g throughout the entire ~2 s interval.
#2 in turn has exactly two possibilies, another true dilemma:
  1. Either g deviated to above g. Then there was some above g at WTC7
  2. Or g deviated to below g. If, throughout the rest of the interval, g was strictly at g, then any non-zero time interval at <g would pull the average to <g also. Therefore, to fix this, g must also have deviated to above g at some other time, to bring the average back to g.
So, the only two possibilities for "no >g at WTC7" - another true dilemma - are:
  1. Either there is no time interval, of 2 s or any other non-zero length, during which a averaged g
  2. Or a = g throughout the entire interval when a averaged g
If 1. is true (all measured intervals with a(avg) = g are mistaken, a < g throughout), then "look, freefall!" is a false premise to begin with, no matter what you might want to conclude from it.
I find 2. to be more implausible than its alternative: I find it more plausible that a was variable at all times. The reason is that, during the time interval in question, the North wall was still one large interconnected structure, and I assume that it was still connected to a significant numbers of floors, so it is far more likely than not that forces beyond gravity were acting on that wall and any point along its roofline.

Therefore, I conjecture some >g to be more plausible than no > g, given the data and analysis that most agree on.
 
@FatPhil @Oystein
For what it is worth at this late stage of WTC discussion. Reference "smarter minds" or at least "other minds"
(But smarter minds with more time to spare have poured over these videos long enough. @femr2 for sure analysed early motion and found lots of it. Has anyone tracked other floors?
In the couple of years following the big split on JREF when members left and started The911Forum. Was that 2007-8?? They did some similar looking graphic work. Mostly Twin Towers (My memories are vague) and before Femr2 did his extensive analyses of WTC7.

They were still trapped in the one-dimensional approximations mode as per Bazant, Szamboti's "Missing Jolt" and mosr other researchers pre 2007 and "ROOSD". Trying to analyse detailed mechanisms from the perspective of gross motions. But the smear images they produced looked similar. I don't think they looked at WTC7. But there are similarities of output.
Some of the motion probably is not actually downward but bending inward.
@femr2's list of about 12 accuracy limitations affecting NIST's work is still available on ISF - I can't access it at present.

:
 
I find 2. to be more implausible than its alternative: I find it more plausible that a was variable at all times. The reason is that, during the time interval in question, the North wall was still one large interconnected structure, and I assume that it was still connected to a significant numbers of floors, so it is far more likely than not that forces beyond gravity were acting on that wall and any point along its roofline.

Therefore, I conjecture some >g to be more plausible than no > g, given the data and analysis that most agree on.
Hence my position. Given that over "G" is possible there is no legitimate basis for dismissing it as bunk in the specific scenario of WTC7. It amounts to a global exclusion claim and is not valid.
 
And before Oystein or someone says anything, okay, let's say it's not the entire building in free fall. Let's say it's just part of the north wall. Well, how do you get that part to drop at 9.8 m/s^2? Unless I'm mistaken, the perimeter wall had steel columns all around. There's support, there's resistance. Or there should be, but there wasn't.
You are in the right thread!

Go to post #1 and play the video clip with the 2 ladders!
The left ladder is measured at more than 1g!
But it is not in free fall!
"There's support, there's resistance."

Measuring free fall acceleration does not prove free fall!
The video in post #1 shows that!


That's the entire point of this thread!


Source: https://youtube.com/watch?v=n8WxkqMRgS4
 
It has no context. That's true.

But I did not say it is out of context, which typically means it's misleading.
It's strange that we have to have these converstations about the meaning of words.

You said the quote was "cherry-picked"; which usually means quoting out of context. Also, surely you were in fact implying that AE was misleading us with the Shyam Sunder quote?

You were dismissing the quote as evidence that NIST says that free fall would imply no resistance. But that is exactly what Sunder says it would imply. He also says that a 40% slower collapse suggests that there was structural resistance.

Sunder may be wrong (or just imprecise) about that. But AE911T is not doing anything tricky with the quote.

Because the context is not provided, I can't check if it's used out of context. ae911 sometimes do that.

This is what I think I've shown is just plain wrong in this case. AE911T puts you one click away from a video of the full context of the quote. They also linked to Chandler's detailed written account of the context in which Sunder said those words.

Again, it's certainly still possible that they're misleading us. But it is not because they're preventing us from understanding context.
 
"There's support, there's resistance."
It want to understand this correctly. When you say "there is resistance" (if that is what you're implying by quoting Henkka there) you mean at the bottom of the rope ladder, right? There is no resistance to the fall of the top rung, right?

In fact,
Negative resistance actually - "tugging down"
We agree that those are the mechanics of this system, right?


Or there should be, but there wasn't.
When we say this, we mean basically that the perimeter columns, which should have resisted the collapse of the facade, seemed to behave more like the ropes of a rope ladder, and did not (apparently) transfer the force of the impact of the bottom of the structure upwards to resist the fall at the top.

(I say "seemed" and "apparently" because I find the whole thing very puzzling. I don't understand how this could happen to a building. So please don't ask me for evidence of controlled demolition or whatever. I have no good working theory of that collapse, of what actually turned the columns into what were effectively ropes. And I take it none of you want to show me how to build a simple working model.)
 
No. We can agree exactly what I said - the single force which @Mendel characterised as resistance - is a downward pull. A force external to the upper part of the system. Pulling downwards and increasing the acceleration of the system above it so that it exceeds "G".
Yes, I think we agree then. If one thinks of "resistance" as a force opposite to the downward motion of the top rung, then there is none in this system. I think when skeptics say there appeared to be "no resistance", that's what they have in mind.
 
Yes, I think we agree then. If one thinks of "resistance" as a force opposite to the downward motion of the top rung, then there is none in this system. I think when skeptics say there appeared to be "no resistance", that's what they have in mind.
If you define resistance as a force opposite tho the downward motion of something, there IS resistance to the top rung: To PART of the top rung!

Whenever the top rung (or any rung) is "tugged" down one end, the other end of that rung experiences an UPward force that resists and slows its lateral downward motion, relative to uninhibitedfree fall.
This is demonstrated by my #3 experiment with the pencil.

If you happen to obeserve the tugged side of the rung, you'll measure >g acceleration downward
If you happen to obeserve the other side of the rung, you'll measure <g acceleration downward
If you manage to observe the center of gravity of that rung, it will be >g, but at a lower rate than the tugged end
If you manage to observe the center of gravity of the entire ladder (all rungs), it will be decidely <g, because of the bottom runs that come to a full stop or for a bit of time even reverese direction.
See all the changes of direction of the forces associated with a single tug that come about merely by observing different points?

That is the core lesson here:
In a structure, any force acting on any part going any direction can translate into a force and acceleration of any other part going in any other direction.
In particular, an upward force here (e.g. where bottom of structure runs into ground) can translate a downward force there (e.g. one edge of the roof).

Because of this, measuring the acceleration of only one part of a strcuture that is moving under the force two or more different forces does not allow you to draw conclusions about the magnitude or direction of forces on other parts of the structure, or the net total of all forces on the whole structure.

Put differently: Seeing motion at or even above g somewhere on the perimeter does not mean there is no structural resistance.
 
What I see there is that all the lines are not horizontal - they drop slightly from left to right starting at the left edge of the image. But the foreground buidling remains horizontal and straight. Therefore, there is downward movement much earlier.
4 pixels is 1 frame of 1/30 seconds?
This strongly suggests that buckling of the North wall columns started earlier than I thought, than perhaps many of us thought.
And that means acceleration early on was less than what Chandler measured, less perhaps than what NIST measured.

Some of the motion probably is not actually downward but bending inward.
Yup, I started that (-ss in the ffmpeg command) at 9 seconds in. The bit on top has already dropped inside the building, scattered windows have been popped out, and the whole wall has begun to resemble a hanging sheet by that stage. And yup, the vid is 30fps, so your calculations are correct.
 
AE911T puts you one click away from a video of the full context of the quote.
I'm not looking for that in a video edited by ae911.

You were dismissing the quote as evidence that NIST says that free fall would imply no resistance.
Was I? Quote me, please.

He also says that a 40% slower collapse suggests that there was structural resistance.
Yeah. Did you forget my explanation for that?
We could've saved ourselves this circular argument if you hadn't quoted me out of context in #84, https://www.metabunk.org/threads/falling-objects-can-be-faster-than-free-fall.13263/post-306394
It's a cherry-picked quote without context, I don't see ae911truth link back to the actual press conference. Sunder's point is that it's not unusual for a collapse to be slower than free fall because of resistance. Now re-read my logic explainer above to understand why that is not the same as saying that resistance means slower collapse.
It's not invalid.
It's like you only preach "taking time to consider someone's points before responding", but don't do it.

Repetition of falsehoods without ever considering rational counter-argument is another trait of believers/truthers, btw.
 
If one thinks of "resistance" as a force opposite to the downward motion of the top rung, then there is none in this system. I think when skeptics say there appeared to be "no resistance", that's what they have in mind.
Skeptics say that? Truthers do.
And they have free fall in mind when they say that.
But your definition just means net zero external force.

Now consider my other example: a rod supported on one end.
20231124_094719.jpg

Even if, by your definition, the center point of the rod suffers "no resistance", would you say it is in free fall?
What about the other points on the rod, undergoing accelerations from 0g to ~2g? Are they in any different from the 1g center point?
 
Yes, I think we agree then. If one thinks of "resistance" as a force opposite to the downward motion of the top rung, then there is none in this system. I think when skeptics say there appeared to be "no resistance", that's what they have in mind.
Please stop it. I said "negative resistance. "Tugging" or pulling. And our discussion is about what I said NOT your speculation about what some unspecified skeptics may say.
 
I'm going to bow out for a while. If I'm understanding you correctly you are saying that the rope ladder that hits the table is not in free fall. There seems to be some technical sense in which that is true and some (net negative) sense in which the "resistance" that the bottom rung encounters is transmitted to the top rung. But, to tell you the truth, I'm having a hard time following the argument and why you think it is important.

By extension, I don't yet see how I could use it in a conversation with someone who thinks WTC7 was an obvious controlled demolition. I don't understand what it would force them to concede they've misunderstood.

So I'll step away and maybe reread this thread in a few weeks. Happy debunking!
 
Ooops. I missed this. Time to repeat a bit of truism:
In part, one wants to refer to evidence; but, in part, one must defer to authority.
Not when the authority is wrong or misleading. I've explained why many times. And it is a major factor in this discussion - the distinction between Free Fall and Free Fall Acceleration. NIST's comments are misleading.
Otherwise one is playing whack-a-mole with facts proffered by anonymous members of forums like this.
Playing "whack-a-mole" is de facto your choice. As is the snide comments about "anonymous members". The test of ANY assertion of fact or reasoning is "Is it correct?" If a member here makes a true statement it is true. And if an "authority" makes a false statement - it is false. And no number of PhDs or published papers will make the false claim by the "Authority" become true.
 
You are in the right thread!

Go to post #1 and play the video clip with the 2 ladders!
The left ladder is measured at more than 1g!
But it is not in free fall!
"There's support, there's resistance."

Measuring free fall acceleration does not prove free fall!
The video in post #1 shows that!


That's the entire point of this thread!

Okay let's just ignore the terms "free fall" and "free fall acceleration" completely and just focus on the numbers. Both of those ladders are going down at approximately 9.8 m/s^2, right? With the one on the left going slightly faster, because of the unique tugging effect. What I'm saying is I can't understand how a steel-framed skyscraper could collapse down through its own structure at anywhere close to 9.8 m/s^2, because there's so much stuff in the way. That's the issue. Buildings aren't rope ladders... Even when massively damaged by airstrikes, they will decelerate and tumble when collapsing:


Source: https://www.youtube.com/watch?v=q7nfYOYLcTU

So the question of the thread should be, how do you get a building to behave like a dropped rope ladder?
 
Ooops. I missed this. Time to repeat a bit of truism:

Not when the authority is wrong or misleading. I've explained why many times. And it is a major factor in this discussion - the distinction between Free Fall and Free Fall Acceleration. NIST's comments are misleading.

Playing "whack-a-mole" is de facto your choice. As is the snide comments about "anonymous members". The test of ANY assertion of fact or reasoning is "Is it correct?" If a member here makes a true statement it is true. And if an "authority" makes a false statement - it is false. And no number of PhDs or published papers will make the false claim by the "Authority" become true.
I think @Landru would agree with me that this off-topic to the current thread. If you want to start another one about evidence & authority in debunking, that's something I would love to discuss.
 
So the question of the thread should be, how do you get a building to behave like a dropped rope ladder?
The thread topic is explicitly clear:

"Falling objects can be faster than free fall"​

And the rope ladder proves that single point.

Nobody is making the silly claim that WTC7 behaved like a dropped rope ladder.

If you don't understand why WTC7 collapsed just ask in an appropriate thread.

Here - this is how you state it in your post in this thread:
What I'm saying is I can't understand..
Great - then take notice of offered and presented help.
how a steel-framed skyscraper could collapse down through its own structure
The topic is WTC7. Not any other or an y generic structure. WTC7 didn't collapse through its own structure. The core collapsed internally followed a few seconds later by the perimeter shell which failed at the bottom causing the shell to drop nearly vertically.
at anywhere close to 9.8 m/s^2,
One part of the perimeter shell was measured as falling at APPROXIMATELY "G" << That much was the agreed starfting premise. If you want to claim it is wrong>>>you are on your own to prove it.
because there's so much stuff in the way.
There obviously wasn't "so much stuff in the way". The challenge is to understand what removed it./




That's the issue. Buildings aren't rope ladders...
That is NOT the issue -that is your derail.

Now is there any aspect of those simple outlined points that you still need to question?
 
So the question of the thread should be, how do you get a building to behave like a dropped rope ladder?
Take a bigger building and a lot more energy than in your example; also, take one with a tube-in-tube design that removes structural elements from much of the floor plan.
Or one where those interior structural elements collapse first. Or both.

As soon as the stiffness is removed from the structure, it collapses like a rope ladder.
Compare cooked and uncooked spaghetti.
 
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