Free Fall

From AE911Truth’s front page list of characteristics:

WTC Building #7…

Symmetrical “structural failure” — through the path of greatest resistance — at free-fall acceleration

…Twin Towers…

Destruction proceeds through the path of greatest resistance at nearly free-fall acceleration

In addition, several slides in the two-hour presentation make the claim of freefall speed (currently slides 43, 70, and 384-386).

Freefall Speeds

Did any of the three WTC Buildings collapse at freefall speeds? No.

The term is a bad one. Speed, or velocity, is a measurement of how fast an object is moving at any one point in time. Acceleration is a measurement of how an object’s speed is changing over time at any one point in time. Free fall is a condition that describes acceleration, not speed.

So if you ask how fast some object is moving, that is speed. If you ask how much an object is speeding up or slowing down, that is acceleration. And free fall is a special category of acceleration: it is the rate of acceleration an object has if one source of gravity is the only force operating on it.

Free Fall Acceleration

Did any of the three WTC buildings collapse at free fall acceleration? Only WTC 7 did, and that was only for 2.25 seconds of its 16+ second collapse.

At one point during the progressive collapse, Floors 7-14 failed completely, and the remaining part of the building above this point began a sudden plummet. It’s this plummet of the upper floors that AE911Truth continues to point to as the beginning of WTC 7’s collapse, but the actual collapse had been underway for a few seconds before this point.

I’ve prepared a short video showing that 7 World Trade took at least 16 seconds to fall completely, with seismic information indicating 18 seconds.

So this short period of the overall collapse is predicted by the NIST computer modeling and well explained by their analysis of the collapse. In fact, the Final Report on 7 World Trade from NIST demonstrates that this part of the collapse (from movement of roofline to disappearance behind other buildings) fell 40% slower than it would have if moving entirely at a rate of free fall acceleration.

AE911Truth’s own materials show this to be true. On slide 71, they reproduce a graphic that gives the overall rate of WTC 7’s roofline fall at 9.1 m/s-squared. Gravity accelerates at 9.8 m/s-squared. This clearly is not free fall acceleration.

As far as the towers are concerned, pictures of both clearly show debris falling separately from the main tower. Separate from the main structure, the only forces operating on those pieces are air resistance (minimal) and gravity. The debris descends at a rate of acceleration much greater than that of the main portion of the collapse.

Perimeter columns from the South Tower are on the left. Perimeter columns from the North are on the right. You can see that these pieces are falling faster than the actual collapse, because they’ve fallen below where they broke off. You can see the undamaged face of the South Tower to the extreme left and the undamaged face of the North Tower to the extreme right.

“Near” Freefall Speeds?

Did any of the three WTC buildings fall at “near” freefall speeds or acceleration?

That all depends on how “near” is defined. An acceleration rate of 9.1 m/s-squared is nearer to 9.8 than 8.7, but it’s further away than 9.7. Trying to define “near” in this case is a fool’s game.

The more appropriate question to ask is, “How fast should these buildings have fallen?” If mathematical analysis takes all appropriate factors into account and shows the buildings fell within an expected time range, then it wouldn’t matter if the buildings fell at free fall acceleration, near free fall acceleration, or much slower than free fall acceleration. There would be nothing unusual about the time at all. If, however, the actual acceleration is outside this range, that would indicate a significant factor that had not been accommodated, one of which could conceivably be controlled demolition.

Such analysis has been done. As NIST explains:

…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.

The section of 7 World Trade in the final part of the collapse is quite similar in mass to the upper sections of the towers.

More rigorous calculations have been published in respected scientific journals (Bazant & Zhou (pdf), and Bazant, Le, Greening, and Benson (pdf)). The results work out to the same conclusion. The dynamic loads of the descending mass was far too large to be redistributed by any structure available to resist them. The acceleration of their descent was not mathematically unusual.

Therefore, the buildings falling at speeds that can be described as “near free fall acceleration,” whatever that vague term means, isn’t something that rules out the buildings falling naturally.

Other AE911Truth Arguments

No Change in Timing?

The argument made by AE911Truth about free fall acceleration has changed in the case of 7 World Trade. Their first couple of presentations described 7 as falling at freefall speed, period. That changed for a while, when they describe 7 as falling at “nearly freefall speed” just as they always have the towers.

However, they continue to say that 7 World Trade fell in 6.5 seconds. You can still see Gage make this claim in interviews available on their front page, and a graphic detailing this claim appears at the link to their “WTC 7 Evidence” page in this paragraph. Wouldn’t they be obliged to change this 6.5 second count if they think the building took longer to fall? Or were they being contradictory before?

Regardless, they have now returned to the unqualified “free fall acceleration” claim for WTC 7. And yet the time of 6.5 seconds continues to be the operative claim for the time it took 7 to fall. Such changes demonstrated a regrettable lack of scientific vigor on the part of AE911Truth.

7 Faster and Slower?

Funnily enough, AE911Truth currently argues that 7 World Trade descended both slightly faster than and slower than the acceleration of gravity!

They use a video in their presentation in which David Chander takes the Dan Rather video and tries to very precisely measure the fall of the building. He concludes that the building fell at an acceleration rate of 10 m/s-squared, which is faster than gravity accelerates! This can be found on Slides 71-72. But on the slide before this, AE911Truth has just argued that the building fell at a rate of 9.1 m/s-squared!

Furthermore, the 10 m/s-squared figure comes from just the first 3 seconds after the roofline begins to fall. Chandler doesn’t measure before or after that. And to be fair to Chandler, he does point out that the actual rate of acceleration by gravity is in the margin of error of his measurement.

But the acceleration rate of 9.1 m/s-squared isn’t.  And according to their own Slide 70 graphic, the 9.1 acceleration rate is constant for the building. In other words, there is no marked change in the rate of acceleration on slide 70.

So the AE911Truth presentation is truly puzzling. It genuinely is arguing right now that the building fell at two different acceleration rates. Using their own figures and graphs, you can see that they don’t have a clue of what they’re talking about.

NIST’s Timing Of Collapses

Another argument you will frequently see about the collapses of the Twin Towers is that “NIST claims the towers fell in 9 seconds and 11 seconds.” However, a look at the report and a FAQ list published by them shows that NIST’s figures are timing from the beginning of the collapses to the time the first exterior panels hit the ground. It’s natural that this time would be quite close to a time free fall acceleration would produce.

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.

As NIST points out, sections of both cores remained standing after the collapse, and any time of total collapse should include the time it took for these structures to fall as well. There’s just no way to get a handle on a precise time for total collapse of these buildings. AE911Truth’s attempt to do so in order to claim “near free fall acceleration” shows their unscientific methods of investigation.