If you do not have the intelligence to comprehend the proof, you do not have any credibility:
From the rooftop of WTC1, drop one dark blue billiard ball over the edge. As it falls, it accelerates. If it were in a vacuum, it would hit the pavement, 1368 feet below, in 9.22 seconds, shown by the blue curve in the figure 1, below. It will take longer if air resistance is considered, but for simplicity, we'll neglect air resistance. This means that the calculated collapse times are more generous to the official story than they need to be.
Figure 1. Minimum Time for a Billiard Ball dropped from the roof of WTC1 to hit the pavement below, assuming no air resistance:
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Notice that the billiard ball begins to drop very slowly, then accelerates with the pull of gravity. If in a vacuum, the blue ball will hit the pavement, 1368 ft. below, 9.22 seconds after it is dropped. That is, unless it is propelled by explosives, it will take at least 9.22 seconds to reach the ground (assuming no air resistance).
According to the pancake theory, one floor fails and falls onto the floor below, causing it to fail and fall on the floor below that one, and so forth. The "pancake theory" implies that this continues all the way to the ground floor. In the case of both WTC towers, we didn't see the floors piled up when the event was all over, but rather a pulverization of the floors throughout the event. (see pictures below) So, clearly we cannot assume that the floors stacked up like pancakes. Looking at the data, we take the conservative approach that a falling floor initiates the fall of the one below, while itself becoming pulverized. In other words, when one floor impacts another, the small amount of kinetic energy from the falling floor is consumed (a) by pulverizing the the floor and (b) by breaking free the next floor. In reality, there isn't enough kinetic energy to do either.
[Hoffman]
911research.wtc7.net
911research.wtc7.net
But, for the sake of evaluating the "collapse" time, we'll assume there was. After all, millions of people believe they saw the buildings "collapse."
Figure 2. Possibilities to consider for modeling the collapse.
Model A: The floors remain intact and pile up like a stack of pancakes.
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Model B: The floors blow up like an erupting volcano from the top down.
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Which of the two models, above, best matches the images below?
Figure 3. Images from the "collapse."
(a) WTC2, demonstrating there is little to no free-fall debris ahead of the "collapse wave," and (b) layer of uniform dust left by the "collapse."
a. i18.photobucket.com
b. i18.photobucket.com
If there was enough kinetic energy for pulverization, there will be pancaking or pulverization, but not both. For one thing, that energy can only be spent once. If the potential energy is used to pulverize a floor upward and outward, it can't also be used to accelerate the building downward. In order to have pancaking, a force is required to trigger the failure of the next floor. If the building above that floor has been pulverized, there can be no force pushing down. As observed in the pictures below, much of the material has been ejected upward and outward.
i18.photobucket.com
i18.photobucket.com
Any pulverized material remaining over the footprint of the building will be suspended in the air and can't contribute to a downward force slamming onto the next floor. With pulverization, the small particles have a much larger surface-area-to-mass ratio and air resistance becomes significant. As we can recall, the dust took many days to settle out of the air, not hours or minutes. So, even though the mechanism to trigger the "pancaking" of each floor seems to elude us, let's consider the time we would expect for such a collapse.
To illustrate the timing for this domino effect, we will use a sequence of falling billiard balls, where each billiard ball triggers the release of the next billiard ball in the sequence. This is analogous to assuming pulverization is instantaneous and does not slow down the process. In reality, this pulverization would slow down the "pancake" progression, so longer times would be expected. Thus, if anything, this means the calculated collapse times are more generous to the official story than they need to be.
‘Progressive Collapse’ in ten-floor intervals
To account for the damaged zone, let’s simulate the floor beams collapsing every 10th floor, as if something has destroyed 9 out of every 10 floors for the entire height of the building. This assumes there is no resistance within each 10-floor interval. i.e. We use the conservative approach that there is no resistance between floor impacts. In reality there is, which would slow the collapse time further. Also, there was only damage in one 10-floor interval, not the entire height of the building. Thus, if anything, this means the calculated collapse times are more generous to the official story than they need to be. Refer to the figure below.
The clock starts when the blue ball is dropped from the roof (110th floor). Just as the blue ball passes the 100th floor, the red ball drops from the 100th floor. When the red ball passes the 90th floor, the orange ball drops from the 90th floor, ... etc. Notice that the red ball (at floor 100) cannot begin moving until the blue ball reaches that level, which is 2.8 seconds after the blue ball begins to drop.
This approximates the "pancaking" theory, assuming that each floor within the "pancaking" (collapsing) interval provides no resistance at all. With this theory, no floor below the "pancake" can begin to move until the progressive collapse has reached that level. For example, there is no reason for the 20th floor to suddenly collapse before it is damaged.
With this model, a minimum of 30.6 seconds is required for the roof to hit the ground. Of course it would take longer if accounting for air resistance. It would take longer if accounting for the structure's resistance that allows pulverization. The columns at each level would be expected to absorb a great deal of the energy of the falling floors. Thus, if anything, this means the calculated collapse times are more generous to the official story than they need to be.
i18.photobucket.com
‘Progressive Collapse’ in one-floor intervals
Similar to Case 2, above, let's consider a floor-by-floor progressive collapse.
Refer to the figure below:
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Total time: 87.9 to 96.7 seconds.
Now, let's consider momentum.
Assume that the top floor stays intact as a solid block weight, Block-A. Start the collapse timer when the 109th floor fails. At that instant, assume floor 108 miraculously turns to dust and disappears. So, Block-A can drop at free-fall speed until it reaches the 108th floor. After Block-A travels one floor, it now has momentum. If all of the momentum is transferred from Block-A to Block-B, the next floor, Block-A will stop moving momentarily, even if there is no resistance for the next block to start moving. If Block-A stops moving, after triggering the next sequence, the mass of Block-A will not arrive in time to transfer momentum to the next "pancaking" between Block-B and Block-C. In other words, the momentum will not be increased as the "collapse" progresses.
Now, recall the physics demonstration shown below. (I believe everyone who has finished high school has seen one of these momentum demonstrations at some point in their life.)
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Note, if some part must stop and then restart its descent every floor, the total collapse time must be more than 10 seconds. Given that the building disintegrated from the top down, it is difficult to believe there could be much momentum to transfer, anyway. Also, consider the energy required to pulverize the floor between each "pancake." After being pulverized, the surface-area/mass is greatly increased and the air resistance becomes significant. I don't believe this pulverized material can contribute any momentum as it "hangs" in the air and floats down at a much-much slower rate than the "collapsing" floors.
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Now, let's consider reality.
QUESTIONS:
(1) How likely is it that all supporting structures on a given floor will fail at exactly the same time?
(2) If all supporting structures on a given floor did not fail at the same time, would that portion of the building tip over or fall straight down into its own footprint?
(3) What is the likelihood that supporting structures on every floor would fail at exactly the same time, and that these failures would progress through every floor with perfect symmetry?
Let's say that we want to bring down the entire building in the time it takes for free-fall of the top floor of WTC1. (Use 9.22 seconds as the time it would take the blue ball to drop from the roof to the street below, in a vacuum.) So, If the entire building is to be on the ground in 9.22 seconds, the floors below the "pancaking" must start moving before the "progressive collapse” reaches that floor, below. To illustrate this, use the concept of the billiard balls. If the red ball (dropped from the 100th floor) is to reach the ground at the same time as the blue ball (dropped from the 110th floor), the red ball must be dropped 0.429 seconds after the blue ball is dropped. But, the blue ball will take 2.8 seconds after it is dropped, just to reach the 100th floor in free fall. So, the red ball needs to begin moving 2.4 seconds before the blue ball arrives to "trigger" the red ball's motion. I.e., each of these floors will need a 2.4 second head start. But this creates yet another problem. How can the upper floor be destroyed by slamming into a lower floor if the lower floor has already moved out of the way?
Case 2, above, shows the red ball being dropped just as the blue ball passes that point.
Remember, I'm assuming the building was turning to dust as the collapse progressed, which is essentially what happened.
So, for the building to be collapsed in about 10 seconds, the lower floors would have to start moving before the upper floors could reach them by gravity alone.
Did we see this? I believe it's pretty clear in some of the videos. The "wave" of collapse, progressing down the building, is moving faster than free-fall speed. This would require something like a detonation sequence.
Realizing that, for example, the 40th floor needs to start moving before any of the upper floors have "free-fallen" to that point, why would it start moving? There was no fire there. And, if anything, there is less load on that floor as the upper floors turn to dust.
In the picture (at right), notice that WTC2 is less than half of its original height, yet has no debris that has fallen ahead of the demolition wave.
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This part of the building surely took a lot longer to hit the ground as dust than it would have if it came down as larger pieces of material.
We know that sheets of paper have a very high surface-area-to-mass ratio and will stay aloft for long periods of time, which is why paper is an excellent material for making toy airplanes. The alert observer will notice that much of the paper is covered with dust, indicating that this dust reached the ground after the paper did.
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In the above picture, there are a few tire tracks through the dust, but not many, so it was probably taken shortly after one (or both) of the towers were down. Also, the people in the picture look like they've just come out of hiding, curious to see what just happened and to take pictures. If there had been a strong wind blowing the dust around, it would blow the paper away before it would have blown the dust onto the paper. So, the fact that much of the randomly-oriented paper is covered with dust indicates the relative aerodynamic properties of this dust.
Also, notice the dark sky as well as the haze in the distance. This was a clear day with no clouds in the sky... except for the dust clouds. This overcast appearance as well as the distant haze can only be explained by dust from the "collapse" that is still suspended in the air.
So, how could the ground rumble for only 8 seconds while WTC1 "disappeared?"
I don't think this part of the building made a thud when it hit the ground.
In conclusion, the explanations of the collapse that have been given by the 9/11 Commission Report and NIST are not physically possible. A new investigation is needed to determine the true cause of what happened to these buildings on September 11, 2001. The "collapse" of all three WTC buildings may be considered the greatest engineering disaster in the history of the world and deserves a thorough investigation.
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