FREE FALL - Did NIST and the 911 Commission get it wrong? [Archive]

Edx

5th July 2009, 05:58 AM

I've just seen someone say that 911 Commission says the South Tower came down in 10 seconds (but we know it was about 15 seconds) and NIST say it collapsed in essentially free fall.

Is there some contextual issue here or what?

He says:

Now obviously the reason why the truth movement and others are making a huge problem over this is because in it states NIST AND the Commission report states it.

9/11 Commission Report wrote:
At 9:58:59, The South Tower Collapsed in ten seconds, killing all civilians and the emergency personnel inside.
9/11 Commission report, Chapter 9, Page 305

NIST wrote:
The building section above came down essentially in free fall, as seen in videos.
NIST NCSTAR 1, Chapter 6, Page 196

T.A.M.

5th July 2009, 06:10 AM

"essentially" free fall, as you can tell is a non scientific, imprecise term. Of course, compared to collapsing over let us say 30-40 seconds, a collapse of 10-15 seconds, compared to the time for free fall, is "essentially" freefall.

freefall time, t....

t2 = (d/0.5a)
t= sq rt of (417m/[0.5x9.8m/s2])
t = sq rt of (85.1)
t = 9.22 seconds

No trouble here...move on.

TAM:)

dtugg

5th July 2009, 06:15 AM

I agree with TAM. As for the 9/11 Commission, it wasn't an engineering report so I don't think it really matters that they said ten seconds when it was actually closer to 15.

Edx

5th July 2009, 06:16 AM

Thats the responce I would have said. Cheers.

~enigma~

5th July 2009, 06:26 AM

I agree with TAM. As for the 9/11 Commission, it wasn't an engineering report so I don't think it really matters that they said ten seconds when it was actually closer to 15.
When ignoring the core. Considering the cores remained standing after the building itself collapsed it was quite alot longer than 15 seconds. As far as NIST's 10 seconds they made it clear that they were referring to exterior panels as was made clear in their FAQ and the many threads here. Does anybody search before posting anymore?

T.A.M.

5th July 2009, 06:30 AM

When ignoring the core. Considering the cores remained standing after the building itself collapsed it was quite alot longer than 15 seconds. As far as NIST's 10 seconds they made it clear that they were referring to exterior panels as was made clear in their FAQ and the many threads here. Does anybody search before posting anymore?

Yah, I mean I think any discussion of free fall time has to ignore the core, because the idea of free fall are objects falling vertically toward earth, and clearly the core (or part of it) did not do that (at least right away), but rather stood after the collapse for a second, then toppled over slightly, then fell vertically.

If you include the core, the time goes up to 18 seconds or more, IIRC.

TAM:)

dtugg

5th July 2009, 06:33 AM

When ignoring the core. Considering the cores remained standing after the building itself collapsed it was quite alot longer than 15 seconds.

Agreed.

As far as NIST's 10 seconds they made it clear that they were referring to exterior panels as was made clear in their FAQ and the many threads here. Does anybody search before posting anymore?

The OP was referring to the 9/11 Commission Report's ten seconds.

~enigma~

5th July 2009, 06:37 AM

The OP was referring to the 9/11 Commission Report's ten seconds.
And the NIST's use of the term essential freefall and they did specifically use a value that was explained in their FAQ or is it you do think the OP searched before asking what according to his post #3 was a purely rhetorical question?

dtugg

5th July 2009, 06:54 AM

Now that I think about it, I think they were actually talking about something else. They said the "section above came down essentially in free fall." This could mean that right after collapse initiation, the section above the initiation point was accelerating at free fall, at least until it contacted the next floor.

Edx

5th July 2009, 08:18 AM

Although... in context it says:

"Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass.”
- NCSTAR 1-6 (http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR%201-6.pdf)

So it says "which were unable to arrest the moving mass", which does seem to suggest that they are saying it provided "essentially" no resistence to "the building section above".

And they dont appear to discern the difference between WTC1+2 since the North Tower took even longer at over 20 seconds to collapse.

How can they say "essentially" free fall when its over double?

:confused:

dtugg

5th July 2009, 08:24 AM

OK. I take it back. What TAM said makes sense.

Edx

5th July 2009, 08:58 AM

Carrying on from my post above...

I found something else in the NIST WTC FAQ:

In other words, the momentum (which equals mass times velocity) of the 12 to 28 stories (WTC 1 and WTC 2, respectively) falling on the supporting structure below (which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum) so greatly exceeded the strength capacity of the structure below that it (the structure below) was unable to stop or even to slow the falling mass. The downward momentum felt by each successive lower floor was even larger due to the increasing mass."
NIST WTC FAQ (http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm)

It says that the floors were "unable to stop or even to slow the falling mass."

So again, this sounds like they are saying there was basically no resistance. Yet clearly there was resistence since they did take substantially longer than free fall.

Can someone explain what Im missing? I cant imagine they could really mean what it sounds like they mean.

~enigma~

5th July 2009, 09:05 AM

Carrying on from my post above...

I found something else in the NIST WTC FAQ:

NIST WTC FAQ (http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm)

It says that the floors were "unable to stop or even to slow the falling mass."

So again, this sounds like they are saying there was basically no resistance. Yet clearly there was resistence since they did take substantially longer than free fall.

Can someone explain what Im missing? I cant imagine they could really mean what it sounds like they mean.No explanation is needed. You are reading into it with a preconceived bias. They did not say there was no resistance. They did say the resistance was ineffectual at stopping or slowing the collapse. Why are you putting your bias into NIST's words?

Edx

5th July 2009, 09:09 AM

No explanation is needed. You are reading into it with a preconceived bias. They did not say there was no resistance. They did say the resistance was ineffectual at stopping or slowing the collapse. Why are you putting your bias into NIST's words?

It says the floors below didnt even slow the collapse, so if Im reading it wrong show me where. Thats why Im asking, because it seems silly for them to write that.

T.A.M.

5th July 2009, 09:41 AM

I think to explain it to the average non-scientific individual, it was best done as they have. Of course there was "some" resistance, but it terms of slowing the progress of the collapse to any appreciable degree (9 seconds versus 10 or 12, or 13. Like I said, I am not including the core spire, as I do not think they are), the lower segment was incapable...see momentum and gravity.

TAM:)

eg. when you squish/crush a piece of paper in your hands, there is "some" resistance, but is it enough to slow the crushing of the paper?

TAM:)

Edx

5th July 2009, 09:46 AM

eg. when you squish/crush a piece of paper in your hands, there is "some" resistance, but is it enough to slow the crushing of the paper?

TAM:)

If free fall is 9.22 seconds and the North Tower took over 20 seconds not including the core, then there was a substantial amount of resistance.

Yet NIST says that the floors werent able to slow the collapse? :boggled: So therefore what DID slow the collapse? Because clearly something did. So I dont see how they can say that.

T.A.M.

5th July 2009, 11:05 AM

If free fall is 9.22 seconds and the North Tower took over 20 seconds not including the core, then there was a substantial amount of resistance.

Yet NIST says that the floors werent able to slow the collapse? :boggled: So therefore what DID slow the collapse? Because clearly something did. So I dont see how they can say that.

Please show me the video where, not including the core spire, the collapse takes 20 seconds?

The only one of the towers I know of that took even close to 20 seconds, was WTC7 if you include the collapse of the penthouse.

TAM:)

triforcharity

5th July 2009, 11:43 AM

EDX,

I like simple terms myself.

For instance, if I were to stand in front of a car, and push on the hood, while someone pushes the gas pedal all the way to the floor, am I going to be able to stop it?? No, of course not. Am I going to give that car a little bit of resistance?? Sure. Will it have any effect whatsoever on the car??? No, absolutely not. This is (IMHO) exactly what they aare saying.

alienentity

5th July 2009, 12:43 PM

If free fall is 9.22 seconds and the North Tower took over 20 seconds not including the core, then there was a substantial amount of resistance.

Yet NIST says that the floors werent able to slow the collapse? :boggled: So therefore what DID slow the collapse? Because clearly something did. So I dont see how they can say that.

The way I understand it, you're talking about the RATE of acceleration here. The structure offered resistance, not to the point where the mass stopped accelerating, and decelerated.

But structure did slow the RATE of acceleration........at no time did the collapse 'slow down' to a lower rate of velocity until the ground level was reached.

Does that make sense?

Edx

5th July 2009, 01:04 PM

Please show me the video where, not including the core spire, the collapse takes 20 seconds?

The only one of the towers I know of that took even close to 20 seconds, was WTC7 if you include the collapse of the penthouse.

TAM:)

WTC7 was around 13.5 if i remember which was the fastest of the 3.

http://www.youtube.com/watch?v=qLShZOvxVe4

Even if it was only 19 seconds, knocking off 4 whole seconds from the timer on this video, its still DOUBLE free fall.

Edx

5th July 2009, 01:09 PM

The way I understand it, you're talking about the RATE of acceleration here. The structure offered resistance, not to the point where the mass stopped accelerating, and decelerated.

But structure did slow the RATE of acceleration........at no time did the collapse 'slow down' to a lower rate of velocity until the ground level was reached.

Does that make sense?

Sure that makes sence, it slowed the rate of acceleration. But they didnt say that, they said it wasnt even able slow the falling mass.

If its falling with no resistance its in free fall so falling at x speed. If the floors below werent able to "even slow the falling mass" then therefore it would continue to fall at the same acceleration as it would in free fall.
If it was slower than free fall then the floors didnt fall at the same acceleration as it would in free fall, therefore they must have been slowed by something. What slowed it? Clearly the floors beneath it. So surely the floors necessarily slowed the acceleration, right?

I totally open to other interpretations, just ones that i can make sence of!

:boggled:

T.A.M.

5th July 2009, 01:17 PM

WTC7 was around 13.5 if i remember which was the fastest of the 3.

http://www.youtube.com/watch?v=qLShZOvxVe4

Even if it was only 19 seconds, knocking off 4 whole seconds from the timer on this video, its still DOUBLE free fall.

listen, I am not arguing that the towers fell slower than free fall.

Here are the issues I have.

I would suspect that NIST, the commission, etc...used video, not audio, for their collapse times. You are talking about loud, maxed out audio that may not, in its entirety ONLY represent collapse.

I think the South tower numbers of 13-15 seconds are more accurate. I would like to see corroborating evidence to confirm RKOWENs 22 seconds for the North Tower.

TAM:)

Edx

5th July 2009, 01:25 PM

listen, I am not arguing that the towers fell slower than free fall.

Here are the issues I have.

I would suspect that NIST, the commission, etc...used video, not audio, for their collapse times. You are talking about loud, maxed out audio that may not, in its entirety ONLY represent collapse.

I think the South tower numbers of 13-15 seconds are more accurate. I would like to see corroborating evidence to confirm RKOWENs 22 seconds for the North Tower.

If it had finished collapsing at about 15 seconds, where is all that sound coming from? Could the core collapse make the same sound as the rest of the building collapse?

Maybe the seismic data can have the final word.

Still, my point is that I CAN understand why they could say "essentially" free fall if they define essentially to add on an extra 5 or 6 seconds onto free fall time. Thats just semantics.

What I CANT understand is why they would then say that the floors beneath didnt even slow the collapse of the falling mass above. Even if we use the 15 second time, surely it still means it slowed the rate of the "falling mass" a whole 6 seconds longer. So did the floors slow the rate of the "falling mass" or not? Why would they even write that?

T.A.M.

5th July 2009, 02:09 PM

As I have suggested, I think they were speaking in laymen's terms, and probably should have said there was "little to no" resistance, in terms of slowing the collapse.

As you have already agreed to, and others have said, it is a semantics issue. We all know what they meant.

TAM:)

Seymour Butz

5th July 2009, 02:14 PM

I have a couple of technical questions:

1- If we were to use a round number and say that the towers fell at 10% slower than free fall acceleration, then how much energy, or kinetic energy, or %age of KE, or whatever term is appropriate, did the building structure absorb as it fell? The same Q for 7 I guess, if we use a 1% slower than FFA?

Basically, I'm guessing that a 10% absorbtion of KE doesn't mean 10% slower then FFA. I'd guess that a 10% absorbtion would mean that it would fall at the square root of 10% ?

I'm sure that there has to be some means to figure this out, but I'd imagine that Max velocity would play into it somehow.

2- for 7, and I'm sure someone's already done this, what is the error range for a youtube?

~enigma~

5th July 2009, 02:19 PM

sylvan8798

5th July 2009, 03:13 PM

Sure that makes sence, it slowed the rate of acceleration. But they didnt say that, they said it wasnt even able slow the falling mass.

If its falling with no resistance its in free fall so falling at x speed. If the floors below werent able to "even slow the falling mass" then therefore it would continue to fall at the same acceleration as it would in free fall.
If it was slower than free fall then the floors didnt fall at the same acceleration as it would in free fall, therefore they must have been slowed by something. What slowed it? Clearly the floors beneath it. So surely the floors necessarily slowed the acceleration, right?

I totally open to other interpretations, just ones that i can make sence of!

:boggled:

I think you may be confusing the terms velocity and acceleration. First of all, if it is falling with no resistance (free fall) then it is not falling at x speed. The speed is increasing uniformly from zero according to v = g*t where g is gravitational constant 32.2 ft/s^2 and t is time.

Consider this: If something of moderate size is dropped from a great height in air, it will fall through the air with its velocity increasing until the air resistance slows the acceleration to zero and a terminal or maximum velocity is reached. The velocity never slows down during this process, it just stops getting larger. Certainly you would say that the air was not able to "SLOW" the falling object, even though the air slows the drop time relative to free fall in a vacuum. It never makes the object move more slowly than it was moving in the moment before.

Second, you are trying to compare the free fall collapse time to the actual collapse time, but NIST didn't do that in their statement. In other words, they didn't say "the floors weren't able to slow the falling mass compared to free fall". They also didn't say "the floors weren't able to slow the collapse time". They said the floors weren't able to slow the falling mass.

Hokulele

5th July 2009, 06:02 PM

I think you may be confusing the terms velocity and acceleration. First of all, if it is falling with no resistance (free fall) then it is not falling at x speed. The speed is increasing uniformly from zero according to v = g*t where g is gravitational constant 32.2 ft/s^2 and t is time.

Consider this: If something of moderate size is dropped from a great height in air, it will fall through the air with its velocity increasing until the air resistance slows the acceleration to zero and a terminal or maximum velocity is reached. The velocity never slows down during this process, it just stops getting larger. Certainly you would say that the air was not able to "SLOW" the falling object, even though the air slows the drop time relative to free fall in a vacuum. It never makes the object move more slowly than it was moving in the moment before.

Second, you are trying to compare the free fall collapse time to the actual collapse time, but NIST didn't do that in their statement. In other words, they didn't say "the floors weren't able to slow the falling mass compared to free fall". They also didn't say "the floors weren't able to slow the collapse time". They said the floors weren't able to slow the falling mass.

What she said.

BigBird

5th July 2009, 07:03 PM

Darat

6th July 2009, 04:34 AM

Several posts which included Rule 12 breaches moved to AAH.

~enigma~ and Seymour Butz stop your bickering or face further moderation action which may include suspension or even banning.

Dave Rogers

9th July 2009, 06:47 AM

It says that the floors were "unable to stop or even to slow the falling mass."

So again, this sounds like they are saying there was basically no resistance. Yet clearly there was resistence since they did take substantially longer than free fall.

Can someone explain what Im missing? I cant imagine they could really mean what it sounds like they mean.

Nobody's picked up one aspect of this specific point, so I'll just chime in here with a couple of points of physics.

First of all, alienentity is right in saying that the deceleration due to structural resistance was always less than the acceleration due to gravity. As the actual acceleration of the block is the difference between the two, the falling mass continued to accelerate, and therefore didn't slow down. NIST's language is rather imprecise here, but in the most pedantic interpretation it's correct.

The second point, though, is that the resistance of the structure wasn't the main reason for the collapse time being significantly greater than the freefall time. Several people have worked this out, the first being Frank Greening (now banned from this site as Apollo20 - it's a long story), and found that the main reason the towers fell this slowly is conservation of momentum. As the upper block fell, it collided with the floors below it, and had to transfer enough momentum to each floor to accelerate it from stationary to falling rapidly. This reduced the acceleration of the falling mass by several times the amount that the resistance of the structure did. A simple "floating floor" analysis, where the floors are assumed to be unsupported by stationary as each is hit by the falling mass, generally gives a collapse time within about 1/2 to 1 second of the time calculated with a complete structure.

Therefore, it's correct to say that the structural resistance was almost negligible; the actual slowing of the collapse was due to conservation of momentum rather than the strength of the support columns.

Dave

newton3376

9th July 2009, 07:29 AM

Therefore, it's correct to say that the structural resistance was almost negligible; the actual slowing of the collapse was due to conservation of momentum rather than the strength of the support columns.

Interesting....is there a thread on here where I can read Greening's work on this?

So you are saying that most of the resistence was not due to the connections (bolts, welds, etc) holding the structure together, but was simply due to the mass that needed to be accelerated from rest.

I've never heard that before but it makes sense.

Dave Rogers

9th July 2009, 07:49 AM

Interesting....is there a thread on here where I can read Greening's work on this?

Best place to look is http://www.911myths.com/html/other_contributions.html, which has seven articles from him as well as some other very interesting debunking work.

Dave

newton3376

9th July 2009, 07:59 AM

Best place to look is http://www.911myths.com/html/other_contributions.html, which has seven articles from him as well as some other very interesting debunking work.

Dave

Will do.

Thanks.

alienentity

9th July 2009, 08:40 AM

Nobody's picked up one aspect of this specific point, so I'll just chime in here with a couple of points of physics.

First of all, alienentity is right in saying that the deceleration due to structural resistance was always less than the acceleration due to gravity. As the actual acceleration of the block is the difference between the two, the falling mass continued to accelerate, and therefore didn't slow down. NIST's language is rather imprecise here, but in the most pedantic interpretation it's correct.

The second point, though, is that the resistance of the structure wasn't the main reason for the collapse time being significantly greater than the freefall time. Several people have worked this out, the first being Frank Greening (now banned from this site as Apollo20 - it's a long story), and found that the main reason the towers fell this slowly is conservation of momentum. As the upper block fell, it collided with the floors below it, and had to transfer enough momentum to each floor to accelerate it from stationary to falling rapidly. This reduced the acceleration of the falling mass by several times the amount that the resistance of the structure did. A simple "floating floor" analysis, where the floors are assumed to be unsupported by stationary as each is hit by the falling mass, generally gives a collapse time within about 1/2 to 1 second of the time calculated with a complete structure.

Therefore, it's correct to say that the structural resistance was almost negligible; the actual slowing of the collapse was due to conservation of momentum rather than the strength of the support columns.

Dave

thx for the clarification