David Chandler forced NIST to admit "free-fall"

[000063]

So your claim is everything for 8 floors was vaporized. Funny, I can't find video evidence of this.

Your turn. Where's the video evidence that 8 floors of the building simply disappeared?

Get back to us on this.

You're wrong, DGM. Ergo is very clearly not actually claiming anything. He's Just Asking a Question.

Of course, we've established over and over that lots of things could've made 7 look a lot like free fall without actually being it.

 

[LSSBB]

Yeah, I should of course have written "acceleration equivalent to free fall". What Griffin implies IMO is that this acceleration can only take place in case empty space/free fall, and that is what I objected to.

I elaborated in the subsequent post (also about my admittedly limited knowledge of constructions btw ) that (I find it plausible) an attached weight would help accelerate the falling object. So no need for floors to evaporate, just a sufficiently limited resistance below these.
Of course, I could be totally wrong, in which case I'd like to be enlightened

By the way, welcome to the party Asbbjorn. Point of clarification to help your narrative of the collapse: the additional acceleration isn't from the additional attached weight per se. It's from the attached weight already falling and applying a force to the external wall, because the external wall is not falling yet or is falling slower due to resistance at the bottom. In other words, the interior is tugging on the exterior.

 

[AsbjornAndersen]

By the way, welcome to the party Asbbjorn. Point of clarification to help your narrative of the collapse: the additional acceleration isn't from the additional attached weight per se. It's from the attached weight already falling and applying a force to the external wall, because the external wall is not falling yet or is falling slower due to resistance at the bottom. In other words, the interior is tugging on the exterior.

Thanks for the clarification. You put it much clearer than I was able to

 

[Robrob]

You're wrong, DGM. Ergo is very clearly not actually claiming anything. He's Just Asking a Question^TM.

Ftfy.

 

[dc1971]

DGM, I was addressing Asbjorn.

Were you addressing or were you just asking questions?

 

[cromwell]

David Ray Griffin, David Chandler, free fall and NIST

I orginally posted this to Alt.Conspiracy

Free fall is possibly the cornerstone of the Truth Movements argument and
David Chandler's contribution, the subject of so much rapture. I
will now explore these claims in detail and show that most of this is
bluster, huge assumption and sleight of hand. David Ray Griffin lays out
his wears very clearly. He makes three claims. The first is,

"One of the most common arguments for the controlled demolition of WTC 7 has
been on the observation that its downward acceleration approximated that of
a free-falling object."(1)

...

Edited by LashL: 

Snipped for compliance with Rule 4. Please, do not copy and paste lengthy tracts of text from elsewhere. Instead, quote a short passage and provide a link to the source.

 

[LSSBB]

Thanks cromwell. It looks like you posted the same thing twice. On first scan, your material, a lot of which there is to go through, looks well reasoned. I just have a few points for you:

• Look up acceleration curves on this forum that were created by user femr2. They are pretty detailed and show the possibility of trans-free fall accelerations (however, not provable to be constantly at free fall for any significant length of time)
• The above point given, nevertheless due to the dynamic effect of leveraging by the interior material on the rigid exterior of WTC7, moments of freefall can be accounted for without resorting to Controlled Demolition as the source.
• The last two points given, it is difficult to comprehend how a Physicist would insist that any evidence in the fall dynamics would necessitate Controlled Demolition. Unless he is afraid to admit he's wrong, that is...

 

[femr2]

Now when objects fall solely under the influence of gravity, they do so by a given amount of acceleration which varies slightly according to where you are on the earth. This value is approximately 9.8m/s².

Only in a vacuum.

So this collapse time of 6.5 seconds

An old measurement I made put it at ~6.6s, though that would need checking against more recent T₀ eastimates.

... is compared to the time that it would have taken WTC 7 if it were in free fall. This is a proximately 6 seconds.

186m in vacuum... 6.16s... approximately 6.2s

As an aside, given the reminder about air resistance, an apple dropped from 186m would take ~8.9s to reach the ground, though the effect is less with larger and heavier objects.

But let's start with that 6.5 second collapse time.

My old calc, as mentioned above, is here... linky

The NIST reports contain no such figure because it is simply not possible to calculate it.

By synchronising multiple viewpoints, a reasonable estimate can be made, as show in the link above...T₀ caveats aside of course.

So what about the claim that buildings that experience control demolition have an average acceleration which is 'almost' or 'essentially' free fall?

Some do, some don't. 1515 Flagler approached similar acceleration to WTC7...

He shows in this simple experiment that control demolition at least in this case, does not collapse typically at free fall acceleration

In at least one other case the same does not hold true. It is entirely down to what structure, and how, so far as I can see from the various I've traced. Some are raipd, some not so rapid.

NIST estimated that the collapse time for this period was 5.4 seconds.

Can of worms. I'll point you to some better measurements if you're interested.

They then calculated the free fall time for the same collapse at 3.9 seconds and concluded that the average acceleration was not free fall and was in fact 40% longer. This conclusion is absolutely correct.

I'm afraid not. NIST measurements are somewhat out.

Based on what I have said already, it becomes clear that
some sleight of hand is going on here.

Always worth verifying measurements yourself before being, er, positive about "absolute correctness".

Not so much a matter of principle, as presentation!!

Acceleration profile of WTC7 has been traced in some detail.

One of many...

SG is my data.

It showed that the 5.4 seconds could be broken down into three stages.

They didn't do a great job of it.

It showed that gravitational acceleration was not typical due to the first and third stages, especially the first, which had seen the façade collapse 7ft in 1.75 seconds. This is where most of the resistance came from and accumulated the 40% greater time over all.

Their T₀ was very badly placed, skewing their results.

It is true that NIST acknowledges 2.25 seconds of gravitational acceleration for the next 100ft

Which is again far from accurate.

As it appears you hold the NIST data with some reverence, I'll dig you out somewhat of a critique of their methods and data in the specific areas you mention, so that you are aware of the issues there.

 

[Oystein]

femr2,

NIST has 5.4 s observed vs. 3.9 s calculated for freefall by the time WTC7 drops out of sight in that video. That's a difference of 1.5 s.

You have observed 6.6 s +/- 0.15 s vs. 6.2 s calculated for freefall all the way to the ground. That's a difference of at most 0.55 s.

Assuming that the building doesn't suddenly accelerate at much more than g after dropping out of sight, it could not close that temporal gap. So this implies that errors adding up to 1 s or more are contained in the above values. I think the most likely candidates are, in order
- NIST misplacing t₀
- You misplacing the end of the fall
- accumulating rounding errors
I assume that calculations for freefall are precise to that one digit behind the decimal, and that NIST managed to correctly determine the time stamp for "drops out of sight".

I remember I agreed that t₀ is probably misplaced, but by how much? It is a tricky thing to place...



@ cromwell:

Chandler and consorts would be correct to assert that ALL structural resistance must have been removed ahead of time or in synch, and not have been overcome by gravity alone, IF both the following were true:

1. Gravity is the ONLY downward force
2. Building is at freefall ALL the time from t₀ to end

Neither premise is known to be true.

If 1. is not true, then the forces giving rise to an observed acceleration of g would be broken down into three compoments: gravity + other downward force - structural resistance
If 2. is not true, and there was a period of less than g, then the required breaking of structural components could easily happen in part before the g-period and in other part after the g-period.

femr2's data contains indications that indeed both premises don't hold true - however NIST's phase 1, <g, seems to be shorter and thus acceleration during that time on average higher, than NIST has it.

 

[femr2]

NIST has 5.4 s observed vs. 3.9 s calculated for freefall by the time WTC7 drops out of sight in that video. That's a difference of 1.5 s

...or 38% over.

You have observed 6.6 s +/- 0.15 s vs. 6.2 s calculated for freefall all the way to the ground. That's a difference of at most 0.55 s.

...or 9% over.

Assuming that the building doesn't suddenly accelerate at much more than g after dropping out of sight, it could not close that temporal gap. So this implies that errors adding up to 1 s or more are contained in the above values. I think the most likely candidates are, in order
- NIST misplacing t₀
- You misplacing the end of the fall
- accumulating rounding errors

NIST T₀ is certainly sub-optimal.

My end of fall should be okay, but I'd need to look at the selected T₀ again, given the work done since the video was created (Feb 2009)

I assume that calculations for freefall are precise to that one digit behind the decimal, and that NIST managed to correctly determine the time stamp for "drops out of sight".

Should be fine, though NIST do round off the timestamps quite harshly.

I remember I agreed that t₀ is probably misplaced, but by how much?

Depends how you define it...

a) At start of sustained vertical descent (of specific fixed feature) (sustained velocity change)
b) At start of any non-trivial sustained motion (to exclude some noise)

By either, NIST placed T₀ poorly.

I'd have to backtrack to find exact details, but if (a), they are around a second out; if (b) then many seconds out.

My T₀ for the 6.6s descent calc is bound to require another look, and is likely to be slightly late.

It is a tricky thing to place...

It is indeed. I think the correct definition is (a) above, but if (b) is chosen as the basis for placing T₀ we're looking over 100s earlier.

For reference...

The NIST data suffers from the following (non-exhaustive) series of technical issues, each of which reduce the quality, validity and relevance of the data in various measures...

• NIST did not deinterlace their source video. This has two main detrimental effects: 1) Each image they look at is actually a composite of two separate points in time, and 2) Instant halving of the number of frames available...half the available video data information. Tracing features using interlaced video is a really bad idea, especially for features changing vertical position. I have gone into detail on issues related to tracing of features using interlaced video data previously.
  
• NIST did not sample every frame, reducing the sampling rate considerably and reducing available data redundancy for the purposes of noise reduction and derivation of velocity and acceleration profile data.
  
• NIST used an inconsistent inter-sample time-step, skipping roughly every 56 out of 60 available unique images. They ignored over 90% of the available positional data.
  
• NIST likely used a manual (by hand-eye) tracking process using two single pixel columns, rather than a tried and tested feature tracking method such as those provided in systems such as SynthEyes. Manual tracking introduces a raft of accuracy issues. Feature tracking systems such as SynthEyes employ an automated region-based system which entails upscaling of the target region, application of LancZos3 filtering and pattern matching (with FOM) to provide a sub-pixel accurate relative location of initial feature pattern in subsequent frames in video.
  
• NIST tracked the *roofline* using a pixel column, rather than an actual feature of the building. This means that the trace is not actually of a point of the building, as the building does not descend completely vertically. This means the tracked pixel column is actually a rather meaningless point on the roofline which wanders left and right as the building moves East and West.
  
• NIST chose an initial trace location which precluded starting the trace before the East Penthouse had already descended (as the East Penthouse obscured their trace location). Consequently they no way of gathering early motion data, or quantifying long term noise levels.
  
• NIST chose a trace endpoint which could not be traced from their selected T₀ time, and so subsequently merged data from two separate traces together, without accounting for change in scaling metric.
  
• NIST used the Cam#3 viewpoint which includes significant perspective effects (such as early motion being north-south rather than up-down and yet appearing to be vertical motion). It also means that each horizontal position across the facade requires calculation of a unique scaling metric, which NIST did not bother to do.
  
• NIST did not perform perspective correction upon the resultant trace data.
  
• NIST did not recognise that the initial movement at their chosen pixel column was primarily north-south movement resulting from twisting of the building before the release point of the north facade.
  
• NIST did not perform static point extraction (H, V). Even when the camera appears static, there is still (at least) fine movement. Subtraction of static point movement from trace data significantly reduces camera shake noise, and so reduces track data noise.
  
• NIST did not choose a track point which could actually be identified from the beginning to the end of the trace, and so they needed to splice together information from separate points. Without perspective correction the scaling metrics for these two points resulted in data skewing, especially of the early motion.
  
• NIST performed only a linear approximation for acceleration, choosing not to further derive their chosen displacement function.
  
• NISTs displacement function, if derived to obtain acceleration/time contains a ~1s period of over-g acceleration. Whilst that in itself is fine, it's at the wrong time, and in their conclusions they ignore it.
  
• NISTs displacement function, if derived to obtain acceleration/time does not suggest a 2.25s period of roughly gravitational acceleration.
  
• The displacement data appears to have been extracted initially from the T₀ pixel column, but using the scaling factor determined for a point above Region B, further skewing the displacement data.

 

[femr2]

Edited by LashL: 

Snipped for compliance with Rule 4. Please, do not copy and paste lengthy tracts of text from elsewhere. Instead, quote a short passage and provide a link to the source.

No link to the original text was provided, making the snip rather hindering.

It's here... https://groups.google.com/forum/?fromgroups=#!topic/alt.conspiracy/gKDwK_EoS48

 

[carlitos]

There are still google groups?

 

[femr2]

My T₀ for the 6.6s descent calc is bound to require another look, and is likely to be slightly late.

Have redone the calc...

~8.8s +/- 0.2s (using NIST T₀)

 

[cromleckderennes]

Happy to oblige

Part 3

The voice you hear is David Chandler

 

[beachnut]

Happy to oblige

Part 3

The voice you hear is David Chandler

Do you think he has a brain tumor or is he insane? Is David Chandler, a failure, why does he adopt crazy 911 truth claims, and does he add to the failure of 911 truth?

Why does Chandler fail on understanding 911? How can people be so dumb on 911 issues?

Do you think only a few nuts believe Chandlers claims?

 

[ozeco41]

Happy to oblige

Part 3

The voice you hear is David Chandler

Time to first lie 49 seconds.

Way back in 2007 I routinely used one of D Chandler's early videos to illustrate the global collapse of one of the Twins. The video was good and showed all the key features. Naturally Chandler did not refer to those aspects in his audio commentary which was his usual mix of lies and bad physics.

So I recommended that people look for what the pictures actually showed with the Chandler commentary switched off. THEN, if they wanted a good laugh OR a reason to vomit (depending on their personal attitude towards lying) turn the audio back on and listen to the commentary now being aware of what the video really showed.

 

[cromleckderennes]

Do you think he has a brain tumor or is he insane? Is David Chandler, a failure, why does he adopt crazy 911 truth claims, and does he add to the failure of 911 truth?

Why does Chandler fail on understanding 911? How can people be so dumb on 911 issues?

Do you think only a few nuts believe Chandlers claims?

Why do you always attack him and not what he's saying. Perhaps it's because you can't.

It tells me a lot that does.

 

[cromleckderennes]

Time to first lie 49 seconds.

Way back in 2007 I routinely used one of D Chandler's early videos to illustrate the global collapse of one of the Twins. The video was good and showed all the key features. Naturally Chandler did not refer to those aspects in his audio commentary which was his usual mix of lies and bad physics.

So I recommended that people look for what the pictures actually showed with the Chandler commentary switched off. THEN, if they wanted a good laugh OR a reason to vomit (depending on their personal attitude towards lying) turn the audio back on and listen to the commentary now being aware of what the video really showed.

I think what he's saying is that the Penthouse collapses but the total collapse of the building in general doesn't start until a few seconds later and for 2.28 seconds the collapse is indistinguishable from free fall.

See Part 2 here

NIST say that collapse starts at a point that Chandler identifies as frame 16 in his video when in fact it doesn't start until frame 40. They have to say frame 16 otherwise their 5.4 seconds of collapse will not fit.

See Part 3

Notice at 3.50 Chandler mentions the bottom 8 floors. It is interesting to note that NIST contracted out the analysis of the collapse of the building accept for the bottom eight floors.

It is the bottom eight floors of support that have been removed simultaneously to initiate the free fall we can clearly see in the video.

See the full lecture from David Chandler

 

[cromleckderennes]

Welcome aboard Geraldo

Bachelor in Metallurgical Engineering speaks

If you have a problem with this then don't ask me ask them

If you dare. They'll destroy you

 

[DGM]

Welcome aboard Geraldo

You know that was a long time ago. Are you just slow?