1)
An addition about the towers collapsing in their 'footprints'. Actually,
this is not at all remarkable. For an object to 'topple over', its center
of gravity needs to move beyond the base of the object. For a huge tower
weighing thousands of tonnes, a hurtling aircraft does not provide even
a fraction of the angular momentum required for this.
in an explosion or collapse or anything, fragments can fly far but the
bulk of the building just HAS to come down in its footprints.

details of a calculation demonstrating this are in the postscript of this
email. The result, though is that plane had about 1/10,000 times of the
requisite energy required to tip the building!
So, the building HAD to fall in its footprints.

2)Also, the claim that the building was designed to withstand an impact of
a boeing 707 comes from a single source which is a document produced by
the Port Authority, typically used for "talking points". There is no
credible substantiation of this claim. Nor is there any evidence that any
investigation of the actual effects of a 707 crash was carried out.

Suvrat
P.S: Details of Calculation

Let us do this for the case  of the two towers. The towers were about 1400
ft~400 m tall and 210 ft~70 m on the base. They would have to tilt by about 8 degrees to tip over.
gain in height of center of mass = 200 m * cos(8) = 200*.01 = 2 m.
[taking a weight of half a million tonnes]gain in potential energy = m g h
= 5*10^8 * 10 * 2 = 10^10 joules.

this energy must come from the initial rotational energy the plane
imparted to the building. This is NOT the initial kinetic energy of the
plane. We can calculate this rotational energy from conservation of
angular momentum. Lets assume the plane hit the top of the building.
Then
p_{plane} * L = I w = M L^2 w/3

[assuming a building height of 400 m, a plane mass of 200 tonnes, plane
speed of 360 km/hr, a building mass of half million tonnes, we find]

w = 3*10^(-4) rad/s.

What is the ratio of this initial rotational energy to the energy required
to tip the building:
(1/2)I w^2 = 1.2*10^6 J

ratio ~ 10^(-4)


On Fri, 9 Dec 2005, Merrick Lex Berman wrote:

a few added items on physics:

seismic spikes:
many articles generally debunk the idea that seismic spikes were caused
by explosives at the base of the towers before the mass of the buildings
struck the ground.   nonetheless i remain slightly skeptical that the
largest spike would occur at the onset of the collapse if the pancake
theory is true.  also it seems odd to me that the towers collapsed
directly onto their own footprints.   i have seen implosions and even
under IDEAL circumstances a lot of things could go wrong.   when a
single plane crashes at a lateral angle into one corner of a structure
like the WTC (which was DESIGNED to absorb a plane impact) i am
skeptical that it would cause such a perfect collapse.  that just
doesn't make sense to me either statistically or mechanically.  the
mechanics would argue that the WEAKENED point would cause a lateral fall.

hot spots:
okay, tell me why molten pools of metal remained too hot to approach and
were visible in space for weeks after the collapse?   and why did the
metal show these characteristics:
*Rapid oxidation and intragranular melting of steel pieces*
The limited metallurgical examination of some of the few pieces of
structural steel that escaped the blast furnaces shows very peculiar
features, such as rapid oxidation turning inch-thick steel into
paper-thin scrolled pieces, cavitation giving steel the appearance of
Swiss cheese, and intragranular melting. These suggest a more exotic
process of destruction than mere explosives.

how did this occur?  you tell me!  and furthermore, why was the metal
IMMEDIATELY hauled away and disposed of, instead of being meticulously
examined?  that in itself is beyond strange... it simply stinks.

building 7:
it did not have significant damage or fire and went straight down.
you've got to be kidding me if you think it was not imploded.  there is
no mechanical stress that has been mentioned (to my knowledge) that
offers even a remotely plausible explanation of the physical collapse of
wtc7.   therefore, one may right question, in my view, the causes of wtc
1 and 2 collapses as well.

lex



Suvrat Raju wrote:

To conclude I find the evidence for the "controlled explosion hypothesis"
scanty at the moment.