The 9/11 Forum

Truly awesome, Enik. A couple of questions, if you don't mind.

How much lighter is the second trial? It bounces, but it doesn't look like it stops in the data; does it arrest?

No period of free fall in initial descent was observed...

We indeed observe periods of free fall. The average of "stop and go" movement results in about 6.6m/s². The first "stop" occurred after a drop of about 0.6m the second after about 2.5m and the third after about 5.5m.


Btw, the term "stop and go" are misleading. There is just no acceleration during the "stop" periods. The collapse moves on.

OneWhiteEye wrote:Truly awesome, Enik. A couple of questions, if you don't mind.

How much lighter is the second trial? It bounces, but it doesn't look like it stops in the data; does it arrest?

The numbers I used were .284 lb/cu. in. for the steel density and .00284 lb/cu. in. for the lighter upper material. The lower one stayed at .284.

achimspok wrote:We indeed observe periods of free fall.

Yes, it does appear that way, how quickly I forget.

Enik wrote:The numbers I used were .284 lb/cu. in. for the steel density and .00284 lb/cu. in. for the lighter upper material. The lower one stayed at .284.

Case 2 has an upper block 1/100th the mass of Case 1? Wow. In the graphs, it looks like there's one big whack followed by essentially freefall descent, although the video does not show a continued descent.

achmispok, I think one of the reasons I keep putting the periods of apparent freefall out of my mind is because my data, like your data above, also shows greater than freefall. I can see where that makes sense in close proximity to the contact interface, it's seen on Enik's graph, but I can't say it makes a whole lot of sense at the roofline or above.

also shows greater than freefall.

We have to consider that the tilt and drift towards south distort the curve a little bit. That adds a small amount of apparent drop. The relation is about 3° tilt adds an apparent drop of 0.8m for the Sauret perspective. Between frame 220 and 310 the antenna tilted about 3°. This might solve the "faster than free fall" problem a little bit.
On the other hand, after the north wall gave way the cap tilted/twisted faster than the antenna by pushing the lower north edge of the cap towards north. This motion might cause a little uncertainty but as long as the roof line was connected to the antenna the twist will not add some significant "apparent" drop.

And there is one more thing to consider:
I got the very same phenomenon for the WTC7 drop. There it appears to be hard data. Imo, the mechanism is obvious. The core/west penthouse dropped at free fall - not above. It sank into the roof for a certain amount and took the perimeter down. The perimeter - once released - also accelerated above freefall for a short distance followed by "usual" free fall.
So if the mass of the core is already in motion and the mass of the core spans the floors like a bow then - once released - the perimeter will shoot down above free fall.
The pattern of the second and third acceleration period for the NW corner WTC1 looks pretty similar.

I watched eniks work. (What a great job!) Well, the perimeter panels compensate the jolts from a collision. That's a different mechanism. Those jolts are a rapid change in acceleration and velocity. The measured duration of the deceleration periods are 10-15 frames (0.15-0.25s) and show just a lack of acceleration instead of bouncing. imo if the core was the "motor" of that collapse similar to the WTC7 then the measured data make a lot of sense.

Here is the data (in csv) as time, velocity (in/s)...first for the steel on steel (6 sets of data), then for the lighter steel on steel (5 sets of data):

Code: Select all

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
0.0500019,-19.201,0.0500019,-19.201,0.0500019,-19.201,0.0500019,-19.2009,0.0500019,-19.201,0.0500019,-19.201,0.0500005,-19.2058,0.0500005,-19.2056,0.0500005,-19.2058,0.0500005,-19.2057,0.0500005,-19.2058
0.100008,-38.3988,0.100008,-38.3987,0.100008,-38.3987,0.100008,-38.3988,0.100008,-38.3986,0.100008,-38.3988,0.1,-38.3639,0.1,-38.364,0.1,-38.3639,0.1,-38.364,0.1,-38.364
0.150007,-57.5923,0.150007,-57.5923,0.150007,-57.5923,0.150007,-57.5924,0.150007,-57.5923,0.150007,-57.5923,0.15,-57.571,0.15,-57.5715,0.15,-57.5711,0.15,-57.5712,0.15,-57.5711
0.200006,-76.7859,0.200006,-76.7857,0.200006,-76.786,0.200006,-76.7858,0.200006,-76.7856,0.200006,-76.7858,0.200001,-76.8428,0.200001,-76.8424,0.200001,-76.8428,0.200001,-76.8428,0.200001,-76.8429
0.250005,-95.9794,0.250005,-95.9793,0.250005,-95.9795,0.250005,-95.9791,0.250005,-95.979,0.250005,-95.9794,0.250001,-96.1144,0.250001,-96.1143,0.250001,-96.1144,0.250001,-96.1146,0.250001,-96.1142
0.300004,-115.199,0.300004,-115.198,0.300004,-115.198,0.300004,-115.198,0.300004,-115.199,0.300004,-115.198,0.300001,-115.386,0.300001,-115.387,0.300001,-115.386,0.300001,-115.386,0.300001,-115.386
0.350002,-134.417,0.350002,-134.418,0.350002,-134.417,0.350002,-134.417,0.350002,-134.417,0.350002,-134.417,0.35,-134.658,0.35,-134.657,0.35,-134.658,0.35,-134.657,0.35,-134.658
0.4,-153.636,0.4,-153.636,0.4,-153.637,0.4,-153.636,0.4,-153.637,0.4,-153.636,0.4,-153.93,0.4,-153.929,0.4,-153.929,0.4,-153.929,0.4,-153.929
0.450009,-172.86,0.450009,-172.86,0.450009,-172.86,0.450009,-172.86,0.450009,-172.859,0.450009,-172.86,0.45,-173.201,0.45,-173.202,0.45,-173.201,0.45,-173.201,0.45,-173.201
0.500008,-192.079,0.500008,-192.079,0.500008,-192.079,0.500008,-192.079,0.500008,-192.078,0.500008,-192.079,0.500001,-192.473,0.500001,-192.472,0.500001,-192.472,0.500001,-192.473,0.500001,-192.473
0.550008,-211.246,0.550008,-211.247,0.550008,-211.247,0.550008,-211.247,0.550008,-211.245,0.550008,-211.246,0.55,-211.237,0.55,-211.238,0.55,-211.236,0.55,-211.237,0.55,-211.236
0.600008,-230.415,0.600008,-230.414,0.600008,-230.415,0.600008,-230.416,0.600008,-230.414,0.600008,-230.415,0.600001,-230.002,0.600001,-230.001,0.600001,-230.001,0.600001,-230.001,0.600001,-230.001
0.650007,-249.584,0.650007,-249.582,0.650007,-249.582,0.650007,-249.582,0.650007,-249.583,0.650007,-249.583,0.650001,-248.766,0.650001,-248.767,0.650001,-248.767,0.650001,-248.766,0.650001,-248.765
0.700007,-268.75,0.700007,-268.75,0.700007,-268.75,0.700007,-268.751,0.700007,-268.75,0.700007,-268.751,0.7,-267.531,0.7,-267.531,0.7,-267.532,0.7,-267.53,0.7,-267.53
0.750007,-287.918,0.750007,-287.919,0.750007,-287.919,0.750007,-287.918,0.750007,-287.92,0.750007,-287.919,0.750001,-286.294,0.750001,-286.294,0.750001,-286.293,0.750001,-286.295,0.750001,-286.295
0.800007,-307.087,0.800007,-307.087,0.800007,-307.086,0.800007,-307.088,0.800007,-307.088,0.800007,-307.086,0.8,-305.06,0.8,-305.06,0.8,-305.057,0.8,-305.059,0.8,-305.058
0.850007,-326.255,0.850007,-326.255,0.850007,-326.256,0.850007,-326.255,0.850007,-326.253,0.850007,-326.255,0.850001,-323.823,0.850001,-323.821,0.850001,-323.823,0.850001,-323.824,0.850001,-323.824
0.900007,-158.764,0.900007,-256.564,0.900007,-345.543,0.900007,-345.534,0.900007,-343.156,0.900007,-345.481,0.9,-38.8369,0.9,-166.168,0.9,-158.115,0.9,-127.702,0.9,-126.643
0.950007,-169.744,0.950007,-230.169,0.950007,-354.797,0.950007,-364.095,0.950007,-364.314,0.950007,-364.745,0.950001,67.6903,0.950001,66.8814,0.950001,40.6815,0.950001,55.3317,0.950001,56.8955
1.00001,-196.334,1.00001,-238.177,1.00001,-374.269,1.00001,-375.129,1.00001,-383.41,1.00001,-384.023,1,48.8745,1,45.4983,1,22.1205,1,39.783,1,39.8658
1.05001,-205.319,1.05001,-235.939,1.05001,-390.905,1.05001,-391.713,1.05001,-394.79,1.05001,-393.958,1.05,11.5152,1.05,6.05885,1.05,8.37055,1.05,29.83,1.05,29.7834
1.10001,-222.883,1.10001,-246.768,1.10001,-407.833,1.10001,-413.497,1.10001,-405.212,1.10001,-403.549,1.1,9.99703,1.1,8.40681,1.1,-10.6305,1.1,-15.6507,1.1,-15.6684
1.15001,-245.509,1.15001,-261.943,1.15001,-419.188,1.15001,-424.601,1.15001,-423.193,1.15001,-422.376,1.15,-41.0947,1.15,-40.3155,1.15,-24.346,1.15,-9.05583,1.15,-8.99549
1.20001,-262.533,1.20001,-265.191,1.20001,-426.106,1.20001,-442.483,1.20001,-441.929,1.20001,-441.143,1.2,-29.3277,1.2,-30.8397,1.2,-45.0481,1.2,-64.6351,1.2,-64.5713
1.25001,-263.183,1.25001,-280.982,1.25001,-422.52,1.25001,-455.031,1.25001,-458.552,1.25001,-460.895,,,,,,,,,,
1.30001,-250.196,1.30001,-291.508,1.30001,-431.454,1.30001,-471.779,1.30001,-474.667,1.30001,-475.187,,,,,,,,,,
1.35001,-269.238,1.35001,-284.15,1.35001,-431.613,1.35001,-486.225,1.35001,-486.298,1.35001,-483.991,,,,,,,,,,
1.40001,-277.586,1.40001,-307.311,1.40001,-436.384,1.40001,-503.628,1.40001,-500.422,1.40001,-501.123,,,,,,,,,,
1.45001,-286.767,1.45001,-312.536,1.45001,-442.592,1.45001,-518.267,1.45001,-517.82,1.45001,-518.94,,,,,,,,,,
1.50001,-297.226,1.50001,-308.94,1.50001,-451.552,1.50001,-532.311,1.50001,-534.566,1.50001,-535.784,,,,,,,,,,
1.55001,-297.345,1.55001,-316.361,1.55001,-451.382,1.55001,-549.366,1.55001,-550.311,1.55001,-548.055,,,,,,,,,,
1.60001,-307.281,1.60001,-321.979,1.60001,-456.443,1.60001,-563.592,1.60001,-561.342,1.60001,-562.108
1.65001,-310.696,1.65001,-325.301,1.65001,-465.937,1.65001,-578.502,1.65001,-578.082,1.65001,-578.839
1.7,-333.229,1.7,-345.423,1.7,-466.653,1.7,-589.585,1.7,-592.841,1.7,-594.952
1.75,-332.08,1.75,-349.392,1.75,-471.411,1.75,-612.664,1.75,-608.548,1.75,-607.625
1.8,-331.414,1.8,-354.409,1.8,-473.203,1.8,-622.978,1.8,-622.526,1.8,-622.158
1.85,-355.722,1.85,-353.298,1.85,-484.886,1.85,-635.679,1.85,-637.487,1.85,-638.708
1.9,-364.105,1.9,-366.491,1.9,-487.044,1.9,-648.086,1.9,-651.259,1.9,-652.903
1.95,-373.867,1.95,-396.148,1.95,-484.961,1.95,-662.411,1.95,-665.706,1.95,-666.589
2,-386.388,2,-413.802,2,-497.38,2,-673.087,2,-680.301,2,-682.081


I can see where that makes sense in close proximity to the contact interface, it's seen on Enik's graph, but I can't say it makes a whole lot of sense at the roofline or above.

If core leads perimeter there can be a short additional force downwards as the floors pull the perimeter down. Just as you showed with detection of "jolts", it's the little things that can provide big clues.

achimspok wrote:And there is one more thing to consider:
I got the very same phenomenon for the WTC7 drop. There it appears to be hard data. Imo, the mechanism is obvious. The core/west penthouse dropped at free fall - not above. It sank into the roof for a certain amount and took the perimeter down. The perimeter - once released - also accelerated above freefall for a short distance followed by "usual" free fall.
So if the mass of the core is already in motion and the mass of the core spans the floors like a bow then - once released - the perimeter will shoot down above free fall.
The pattern of the second and third acceleration period for the NW corner WTC1 looks pretty similar.

and

Major_Tom wrote:If core leads perimeter there can be a short additional force downwards as the floors pull the perimeter down. Just as you showed with detection of "jolts", it's the little things that can provide big clues.

I play with that idea from time to time, even did a few pages back in this thread:

http://the911forum.freeforums.org/a-small-point-t358-75.html#p10868

I resort to a sequence of small failures providing a sustained series of impulses to account for the duration of these excursions at or near freefall, for the simple reason that nothing in the building was especially flexible. Nothing stretches. The mechanism of the core leading the perimeter and bowing the floors downward toward the center does seem possible, also.