The 9/11 Forum

David Chandler's "WTC7 in Freefall":
http://www.youtube.com/watch?v=gC44L0-2zL8

He measures an acceleration of 9.885 m/s^2 for approximately the first 2.5 seconds of WTC 7 collapse.

I know that other people are making similar measurements. What values are they getting for the first 2.5 seconds?

Is there any good reason to doubt David Chandler's results? Has anyone tried to reproduce them using his techniques?

Bofors:

I made this post on Sept 11th on page 6 of the Withering critique of the new WTC 7 report thread:

"I think David Chandler has done some good work with his little video but I do have one complaint. This is with his selection of t(zero). Even looking at the velocity plot he displays in his video I would move his t(zero) cursor a tad to the left which would slow his acceleration significantly ......

This has prompted me to do some sensitivity tests on some of my own collapse plots. I have taken one of my "best efforts", which generates a very smooth curve, and looked at the effect of shifting t(zero) by just 0.1 seconds. When I do this I get these two curves:

The original plot fits to:

Drop = -0.077t^3 + 4.8433t^2 -0.2123 t + 0.0669

And the plot shifted by 0.1 seconds gives:

Drop = -0.0176t^3 + 4.4721t^2 - 0.5854t + 0.0034

Hence for the acceleration, by double differentiation, we have:

Original plot:

Accel = 9.6866 - 0.462t

Plot shifted by 0.1 seconds:

Accel = 8.9442 - 0.1056t

Thus we see a marked change in the calculated acceleration for just a 0.1 second shift. This is why I have argued that the measured acceleration is about 9.2 +/- 0.6 m/s^2.

This means the collapse of WTC 7 is still VERY fast, and WAY FASTER than NIST says, but certainly NOT at free fall!" Dr. G

Hey bofors:

NIST says David Chandler was right!

Damn, why am I still going to do my own work to find out?

___
Edited to change the 'b' in bofors to lowercase. And to say again, he might be right, anyway. Or they both (unlikely bedfellows) may be wrong.

I have recently seen some people, (on another 9/11 Forum), claim that NIST never ruled out free fall for WTC 7.

However, just to keep the record straight:

NIST stated in August 2008:

"WTC 7 did not enter free fall"

(See Questions and Answers about the NIST WTC 7 Investigation)

But by November 2008 NIST stated:

"The north face descended at gravitational acceleration ..... This free fall drop continued for approximately 8 stories"

(See Final Report Chapter 12 page 602)

Sad, so sad. Thanks for putting the record straight. Too bad few will ever read it.

PS you got post 1313. Just wanted to point that out.

OneWhiteEye:

Thanks.......

If you take NIST's Final Report data on face value it shows that the resistance to total collapse offered by Building 7 dropped from about 700 MN to zero during the first 3.2 seconds of collapse when the roofline had dropped 17 meters or 4 floors.

But by 4.8 seconds, the resistance had been fully restored so that, after an initial increase, the acceleration deceased from ~ g to zero by the time the roofline drop was 56 meters or 14 floors.

This is all very strange!

A professor of mine, when asked about the third derivative of position, replied to this effect:

It's called jerk and doesn't figure significantly in classical mechanics. I'm not sure if it's called that because of the obvious physical connotation or because people who introduce it into their calculations are, well, jerks.

Yes, Dr. G. Quite strange. I'm getting the idea that anything goes, as long as it comes from a certain corner. It's a little bewildering, and maybe more so deflating. At least for me. I'm not sure there's any point to correctness; A) no one's listening, B) no one cares and C) people believe whatever they want independent of evidentiary support. To the point that NIST can do a 180 and it's interpreted to be not only 100% consistent but a detailed confirmation of the previous position. To the point where people invent attributions and, when they can't find them, cling to them anyway. To the point where interpolations peaking at greater than g are taken to mean constant g by those publishing them.

I'm a little disillusioned, soon to be sitting on a mountain of useless data.

take hope, OWE. the truth is viral. build it, and they will repeat it.

Thanks, newton. A little encouragement goes a long way.