Reply #8: I think the minimum time would be longer.

[janedoe]

The Case for Controlled Demolition.

For the following, I used the height of The World Trade Center Towers as 1350 feet and considered each floor as (1350/110) feet. Gravity = 32.2 ft/sec^2.

The official collapse time I first read was 8.4 seconds. Later, I read it was 10 seconds. I think the official story gives the time it took for the damaged zone to reach the ground in free-fall, not even the rooftop, as the total collapse time. But, this difference is small. Here, I will use the full height of the building. (This difference benefits the official story.)

Case 1.
Imagine this exercise with billiard balls. 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 (1350 feet below) in 9.490 seconds, shown by the first blue curve in the figure (Figure_1.jpg), below. It will take longer if air resistance is considered. For simplicity, we'll use the "no-air resistance" case. (This difference benefits the official story.)

Note, as the ball begins to fall, it accelerates. If the entire building is to collapse in 9.5 seconds, the other floors must start falling before the ball reaches that floor. This makes the "pancake theory" or "progressive collapse" theory impossible.


Figure_1.jpg

Case 2.
Now, let’s simulate a beam collapse every 10th floor. (This difference benefits the official story.) Refer to the figure (Figure_1.jpg),above. 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.
This approximates the "pancaking" theory, assuming that each floor between the “pancaking”
(collapsing) floor provides no resistance at all. (This difference benefits the official story.)

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. As you can see, a minimum of 32 seconds is required. Of course it would take longer if accounting for the differences I've noted.

Now, let’s consider another scenario, considering momentum.

Case 3.
Assume that the top 10 floors stay intact as a solid block weight (Block-A). Start the collapse timer when the 100th floor fails. At that instant, assume floors 90-100 miraculously turn to powder and disappear. So, Block-A can drop at free-fall speed until it reaches the 90th floor. After Block-A travels 10 floors, it now has momentum. If all of the momentum is transferred from Block-A to the next floor (or floors), Block-A will stop moving, even if there is no resistance for the next floor to start moving. Recall the physics demonstration shown below. (I believe everyone who has finished high school has seen one of these demonstrations at some point in their life.)

http://scientificsonline.com/product.asp_Q_pn_E_3081502


So, if some part must stop and then restart its decent every 10 floors, the total collapse time must be more than 10 seconds. Also, consider the energy required to pulverize the 10 floors between each “pancake.”
Questions:

Now, consider reality. How likely is it that all supporting structures on a given floor would fail at exactly the same time?
What if all supporting structures on a given floor did not fail at the same time?
Would the building tip over or fall straight down into its own footprint?

Case 4.
Similar to Case 1, above, let's consider a floor-by-floor progressive collapse.
Refer to my figure below:

Figure_3.jpg

If the progression begins at the top, it takes about 100 seconds to collapse the building to the gound. If you want to use the 85th floor as a starting point, cut the lower 25 floors off the chart and it takes about 75 seconds. However, the top 25 floors must also have time to drop.

Now, consider the "stuff" flying out horizontally from the building. If the building were falling from gravity alone, it would take even longer to fall because a lot of the gravitational energy would be spent in the horizontal direction. (Actually, the horizontal and/or vertical motion and pulverization would consume many more times the available energy from just gravity alone.)