New collapse footage of WTC7 and North Tower - Nov 2008

[El Nino]

On a side note: Vote O'Cain '08'
For More of the Same!

[yodajazz]

This reply puts it this way:

Re post the characteristics of controlled demolition for all the so called "Debunkers"

#1.Sudden onset.
#2.Symmetrical collapse
#3.Near free fall speed.
#4.Total collapse{Not partial or localized}
#5.Sliced steel.
#6.Pulverization of concrete.
#7.Pyroclastic dust clouds.
#8.Horizontal ejections.
#9.Demolition rings.
#10.Eyewitness testimony of explosions.
#11.Molten metal.

Good evidence listing. My question would be: Why was there a symetrical collapse of WTC 7 if the damage came from the side of the twin towers?

[thx1138]

More evidence of 9/11 pre knowledge:
http://www.prisonplanet.com/ex-cia-m...rk-on-911.html

[trish]

We had a discussion of this in this forum during the summer months. Since than I thought a little more about and came up with the following:

THE PIP MODEL OF TOWER COLLAPSE:
The following is a quick analysis of the physics, not the engineering, aspects of tower collapse. The model that is presented is an idealization based on the physics of Galilean free fall and Newtonian conservation of momentum. We ignore the engineering and architectural geometry because our concern here is merely with the physics of collapse, the order of magnitude calculations of the released energies and dynamics of the fall.

Let’s just consider for the moment the fastest falling pancake model of collapse. It’s an admittedly idealized model based on two assumptions:

1) When the falling upper segment of the tower crashes onto the floor directly beneath it, the collision is perfectly inelastic; the momentum of the upper segment before the crash is equal to the momentum of the moving augmented segment after the crash. (The falling portion of the tower before the crash is augmented by the floor it collided with after the crash).

2) Between crashes the upper segment of the tower free-falls one story to the next floor.

Let call this model the Perfectly Inelastic Pancake (PIP) model. It is the most idealistic of the pancake models of collapse and the fastest of all the pancake models.

Let M denote the mass of the tower. If f is the fraction of the tower that is falling at time t, and if u is its velocity at that time, then the momentum of the fall at that time is fMu. If at that moment the falling upper segment crashes onto the floor directly beneath it and sets it in motion with velocity v, then the momentum after the crash is (f + 1/N)Mv where N denotes the total number of floors the tower had. By the assumption of conservation of momentum,

fMu = (1 + 1/N)Mv.

This allows us to solve for v given f, M and N. Now if s is the spacing between floors and if Dt is the time it takes the falling portion of the building to drop through distance s to the next floor, then by assumption (1),

(-1/2)g (Dt)^2 + v Dt = s.

Here g is the acceleration due to gravity. Since s, g and v can be found, this can be solved for the time to fall one floor, Dt. Caution: the result will depend on the floor. The time between successive crashes (we will show) diminishes with the collapse of the tower.

Now that we know the initial velocity v of this interval of free-fall and its temporal duration Dt, we can compute the velocity u + Du at floor level using


u + Du = g Dt + v.

Now we can just repeat the calculations iteratively to model the folding up of the tower; i.e. reset u = u+Du and f=f+1/N etc.


Now to apply the model, let N=110, and suppose the collapse begins on the 80th story. Further suppose s = 12 feet, and M=0.5 million tons. The following Mathematica program (posted here as a jpg file below) iterates the above procedure starting with these initial conditions to produce a graph of the fall.

AN EXERCISE:
Imagine a 110 story tower. Let the total mass, M, of the tower be half a million tons and the spacing, s, between the stories be 12 feet. Suppose the supports of the 80th floor suddenly fail and the upper segment of the tower from the 80th floor up falls freely onto the 79th floor. Show that the velocity, u, at the time of collision with the 79th floor is 8.47 meters per second (18.9 mph). [Hint: Recall in free-fall u^2 = 2gs]. Show that the velocity, v, of the augmented segment from the 79 floor to the top after the collision is equal to 8.17 m/s (18.29 mph). [Hint: By the conservation of momentum ((110-80)/110)Mu = ((110-79)/110)Mv]. Show that the amount of energy "lost" during this collision is 304 million joules (equivalent to 146 pounds of TNT). [Hint: The kinetic energy before the collision is (1/2)((110-80)/110)Mu^2 and the kinetic energy after the collision is (1/2)((110-79)/110)Mv^2]. This is the energy made available by the collision. The presumption of this model is that this energy is sufficient to cause the immediate failure of the 79th story supports. Below we show each successive crash releases ever greater energies. The final supports are exploded by a collision that makes available an energy equivalent of 1.2 tons of TNT.

SUMMARY:
The above model assumes that each successive clash of tower with floor is completely inelastic; i.e. after the collision the two fall together at the same speed. Generally the sum of potential and kinetic energy is not conserved in inelastic collisions. The imbalance is due to the generation of heat, vibrations, breakages etc. For the example: the energy loss graph (posted here below) illustrates, in terms of tons of TNT, how much energy is released for these purposes with the passage of time. A more detailed model would have to include the geometry of all the support structures holding the floors in place and one would have to know all their physical thresholds. Because these features are not included in the model above, the PIP analysis will be the pancake model of quickest descent. The last graph above compares the PIP predictions with free-fall. Notice the time of fall predicted by PIP is 8.8 seconds compared to the time of free-fall which is 7.7 seconds. Free-fall is the idealization of collapse through well timed sequential demolitions. The idea is that explosives are used to knock out the supports of each floor before the falling segment actually crashes with floor below it. Hence there is nothing to interrupt its fall.
Obviously the example chosen above is similar in initial characteristics of the fall of the World Trade Center Towers in 2001. Those collapses, started between the 74 th and the 95th story and are reported to have taken 10 seconds. The free-fall model and the PIP model both give reasonably accurate predictions of this single temporal parameter. This doesn't mean that pancake models of collapse cannot be eliminated from consideration. But to do so one would have to show that no model of this family can 1) produce the energies required for support failure and at the same time 2) produce a collapse that concludes within the approximate 10 second window.

The PIP model obviously comes in under the window. Moreover, the available energy chart for the PIP model demonstrates that after one second each crash releases more energy than two tenth of a ton of TNT, enough to sustain the continued collapse of the tower. In the case of the WTC towers the initial collapse was preceded by a jet fueled fire. The melting point of steel is beyond the combustion temperature of jet fuel. However, for many centuries baker's have known that wood fueled brick ovens can be built to achieve temperatures well beyond the temperature of an ordinary campfire. This is because ovens are insulated and built of materials of high heat capacity. The heat of the wood fire accumulates within the oven, raising its temperature. There were 60 tons of jet fuel emptied onto the floor of the breached story of the first tower and the first few stories below it. One ton of jet fuel, when burned, will release an energy equivalent to 15 tons of TNT. Sixty tons will release the energy equivalent of 900 tons of TNT, or 3.6 billion BTU of heat energy. A tiny portion of this would be enough to raise the temperature of the steel girders, bolts, plates and other steel structures to the buckling temperature of 1500 degrees F. Once the heat expanded steel was weakened to this threshold, the damaged floor would simply fold away like tin-foil under the one eighth million tons of building above it, initiating a self-sustaining collapse of successively higher energy collisions.

[chefmike]

Thanks for putting it in terms I can understand, trish.

I know wood ovens.

Although I prefer a blend of hickory and oak instead of jet fuel.

[yodajazz]

...

Sound like you are saying that the official collapse version is possible, but I may be wrong. Is that what you are saying? Still I have a basic question. Why does jet fuel not melt the engine metal if it is hot enough to make the metal structure of the WTC? But now that I think about it, the plane crash did release a lot of energy at one time.

[thx1138]

Jet fuel burns very hot but only for a relatively short time. Once it's burned up the fire continued with the burning of the internal materials like wood, paper etc. The collapse could have neen facillitated by partially severing key steel connectors in the weeks prior to the event. A bush relative was in charge of building security at the time. An interesting coincidence. And very fortunate for Larry "pull it" Silverstein who then did not have to pay billion$ for asbestos remediation.

[trish]

Jet fuel burns fast when "fanned" by the air stream rushing through the turbines at hundreds of miles per hour (essentially matching the speed of the plane through the atmosphere). The high altitude air going into the turbine is cold and coming out it's hot. So not only does the airstream through the turbines provide sufficient oxygen for a quick burn, it carries away the tremendous heat of combustion (answering Yodajazz's question).

In the oven of the twin towers, there was much less oxygen and consequently a slower burn and the heat was confined by the insulated walls of the buildings. The heat was stored in the concrete and steel just as the walls of a wood fueled oven store up heat and reach temperatures many times higher than that of an open wood fire (as chefmike, being a chef, is aware...hi).

Yes, the pancaking model of collapse is consistent with the facts as I'm aware of them.

[thx1138]

Trish: how do you explain the pools of molten iron at the bases of the WTC towers after the debris was removed? Iron's melting point is far above the temperature generated by burning jet fuel according to what I've read.

[thx1138]

Less oxygen? the buildings had big holes and the wind was blowing into them fanning the fires.