Quote from Maverick1:
Further, probably the most troubling evidence suggesting the use of explosives
is the near free fall speed of the towers, which should have taken much longer
than 9 seconds to collapse if it was a structural failure.
What is your evidence for this estimate and what on earth kind of reasoning
are you using to determine how long the collapse
should have taken?
I do, certainly, agree that this time scale is a critical parameter in
theorizing about the collapse. But your claim of 9 seconds seems
highly
suspect to say the least.
The towers are reported to have been (approximately) 416m tall. This
corresponds to a collapse time to ground level, in free fall, of 9.21 s.
A collapse time equal to or less than free fall time seems neither possible
nor believable to me under any imaginable mechanism.
The shortest possible approach of the collapse time to free fall I imagine
could be achieved only in the case that
all supporting structures are
cut simultaneously, in which case all parts of the building would begin
accelerating towards the ground at the same time. If then, there were
no
further resistance at all to the downward force of gravity, which is
certainly not true in reality, then some material from the tops of the towers
could completely reach the ground in the free fall time, but certainly not
before.
My experience is that it is
very hard to pinpoint total collapse times
either from the video evidence or from the seismic data.
I did in fact try to do it on my own several years ago, and came up with an
upper bound for the collapse of the dust cloud from the North tower (as seen
on the CNN video) to the ground of about 13 seconds, counting from the time
that the radio antenna
appears from this vantage point to begin to
fall. The South tower is much harder to deal with.
The seismic data consist of spikes extending over many seconds and starting at
the earliest at least some 10 seconds
after the putative initial points
of collapse.
NIST gives the following, rather more complex, and far more complete
discussion. Since you are talking about the official story in some of the
below, I think it would behoove us all to actually read the official story and
to get it straight, so I am going to quote at some length what is actually
said relative to the time scales of the collapse:
http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm
6. How could the WTC towers collapse in only 11 seconds (WTC 1) and 9
seconds (WTC 2) speeds that approximate that of a ball dropped from
similar height in a vacuum (with no air resistance)?
NIST estimated the elapsed times for the first exterior panels to strike the
ground after the collapse initiated in each of the towers to be approximately
11 seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed
times were based on: (1) precise timing of the initiation of collapse from
video evidence, and (2) ground motion (seismic) signals recorded at Palisades,
N.Y., that also were precisely time-calibrated for wave transmission times
from lower Manhattan (see NCSTAR 1-5A).
As documented in Section 6.14.4 of NIST NCSTAR 1, these collapse times show
that:
´⦠the structure below the level of collapse initiation offered minimal
resistance to the falling building mass at and above the impact zone. The
potential energy released by the downward movement of the large building mass
far exceeded the capacity of the intact structure below to absorb that energy
through energy of deformation.
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.¡
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.
From video evidence, significant portions of the cores of both buildings
(roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood
15 to 25 seconds after collapse initiation before they, too, began to
collapse. Neither the duration of the seismic records nor video evidence (due
to obstruction of view caused by debris clouds) are reliable indicators of the
total time it took for each building to collapse completely.
Summarizing:
[0] The
first exterior panels from the towers hit the ground in 11
seconds (North Tower) and 9 seconds (South Tower).
[1] Large parts of the
lower core structures remain standing for 15 to
25 seconds after the initiation of the collapses before these began finally to
collapse.
The reality seems a lot more complex than your summary, no?
`the near free fall speed of the towers, which should have taken much
longer than 9 seconds to collapse'
The reinforced HUGE 47 steel slabs in the middle/core represented tremendous
resistance and were DESIGNED to support the buildings in the event of a fully
loaded 707 crash into them.
http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm
`As stated in Section 5.3.2 of NIST NCSTAR 1, a document from the Port
Authority of New York and New Jersey (PANYNJ) indicated that the impact of a
[single, not multiple] Boeing 707 aircraft was analyzed during the design
stage of the WTC towers. However, NIST investigators were unable to locate any
documentation of the criteria and method used in the impact analysis and,
therefore, were unable to verify the assertion that â⦠such collision
would result in only local damage which could not cause collapse or
substantial damage to the building.â¦'
In fact, as we all know: the planes that crashed into the towers were 767s:
jumbo jets which did not exist -- had not even been conceived of -- when the
towers were designed in the 1960s.
A 707 flying at typical take off speeds near New York is
not at all
equivalent to a 767 flying at near full power ... it's a different kettle
of fish entirely. The 767s had far greater kinetic energy than could have been
imagined for the 707, about 7 times greater in fact, due to the greater mass
and greater velocity, obviously. Correspondingly 767s would be expected to do
far greater damage on impact.
More importantly: there is also greater chemical energy carried in the fuel of
the 767 than there would have been in the fuel of the 707.
Chemical energy of the fuel is certainly the dominant factor in both cases.
This is not hard to calculate.
And yet they collapsed in under 10 seconds an hour after the fires burned?
Other buildings in history have burned for 24 hours and still not collapsed,
let alone collapsed at near free fall speed.
In the first place: `collapsed in under 10 seconds' is clearly a questionable
claim on your part.
In the second place, the design of these buildings was unique for the
time. The design does have a high fraction of empty internal space, much
higher than was typical in other high buildings of the time. All of this is
very well known.
This is why I, for one, can
imagine that the structure, suitably
weakened can in principle collapse within a time that is
on the order of
the free fall time, though certainly not a time which is equal to or less
than the free fall time, as it seems you claim
actually happened.
And yet they tell you that jet fuel fire (not a plane crash) combined with
curtains and carpets was responsible for compromising the structural integrity
of those massive core steel slabs. Sorry, the towers did NOT have a hollow
middle. They had exactly the opposite.
This also looks like an incorrect version of the official story.
When one puts all these pieces of evidence together, the near free
fall of the towers, the abundance of reports of explosions both BELOW and
ABOVE, the pulverized dust and cloud, the squibs, the power down on 9/8 and
9/9, the shipment of all the steel and scrap metal to Asia to be melted
allowing no testing to be done for explosive traces, the complaints of the
relatives of the victims re the way the 9/11 commission investigation was
handled ad nauseam, one really has no choice, if one is intellectually honest,
to seriously question the official account of what really happened that
day.
I'm not convinced by your arguments, given the errors that I believe are
present throughout your discussion above. One has to in the first place, get
the official version correct, in order to be able to question it, I think.
I look forward to your next response, and I promise to review the testimony of
the firefighters and respond later, although I think my opinion on it is not
very likely to change.
Thanks also to Bitstream and others who have posted additional interesting
evidence.
Cheers!