This is not a political question. I want to know what people with a scientific background think.?

Question

1. A Boeing 767 travelling at 590 mph has more energy than a Boeing 757 travelling at 530 mph. (Bigger plane - more mass, higher speed, therefore more kinetic energy). Also walls of reinforced concrete and steel can sustain greater impact than sheets of glass and steel. How did the 757 plowed through more than 235 feet of concrete and steel (Pentagon) and the 767 couldn't even go through 208 feet of glass and steel (WTC tower 2)?

2. A 1368 foot tall building with 110 floors (approx 12.44 ft per floor) takes 96.9 seconds to collapse under the "pancaking" or "progressive collapse" theory. The WTC towers took close to 10 seconds. 9.25 seconds is the free fall time from the top of the towers. I have explained this in the section below.

3. Gravity on the earth's surface points downwards. If no other forces are introduced and the resultant is still vertically downwards, why are there plumes and projectiles going sideways and upwards in the videos of the WTC collapse?

The pancaking implies that the top floor collapses on the floor immediately below it and that impact makes the lower floor collapse as well. This implies the second floor from the top can't start moving till the top floor has reached it after falling through 12.44 feet. The third floor can't start moving until the 2nd floor reaches it.. and so on. So each floor has to fall 12.44 ft independently before the floor below it collapses. Adding the time taken for this "progressive collapse" you get 96.9 seconds.

enginerd, I see most of the answers you have written are outside the realm of science. I suggest you stick to those fields. No one is claiming perfect knowledge, and the questions I asked are not extremely detailed either. And Occam's razor (catchy term, huh) has been applied to arrive at these questions. If two projectiles with different energies hit the same material the one with more energy will penetrate further. Occam's razor right? So obviously the deeper hole was made by something with more energy.

I already explained #2 in detail. The assumptions are extremely unfavorable to me. This model assumes that a floor starts moving as soon as the one above it reaches it. In reality the whole fracturing would take some time and would INCREASE the total time. This model calculates the LEAST time it should take.

#3 really couldn't be any simpler, right? Might I mention conservation of energy? Or was that an optional topic where you learned your engineering?

Just a side note: I have a degree in rocket science (or aerospace engineering in more mundane terms.) And how long it took for the structure to collapse: 8-12 seconds. Source: Official 9/11 commission report and lots of video footage. Not happy? Ok I'll assume 15 seconds. Still nearly 6 times as small as 97 seconds. It's a difference of 5-10 seconds. It's more than a multiple of 5.

For some people I think I need to see your diplomas before I even start reading your answers. Hehe..

Answer 1

3. Because there are other forces introduced.

2. Can't answer. I'm not a structural engineer.

1. More of an answer for a structural engineer. I think you are looking at these structures and making assumptions on how they should handle under certain stresses. Hopefully an engineer can answer these questions for you.

They are interesting questions, though. I'm sure engineering courses will use these incidents in courses for some time to come.

Careful with the anomaly hunting, though. It's the usual way people wind up in Grand Conspiracy Land and miles away from reality.

Answer 2

The analysis I saw said that because the initial collapse happened a third of the way or so down the tower, it immediately set a huge mass in motion. The impact on the floor below was so great that it collapsed virtually immediately, hardly slowing the falling mass. As the falling mass was accelerating, it soon had so much momentum that the energy absorbed by the lower structure was insignificant.

As for stuff flying in all directions, that's pretty much the nature of impacts. Also, structural members failing by buckling produce lateral forces, and there would have been some lateral forces in the structure to begin with that were released in the collapse.

Don't know enough about it to comment on the level of damage at the Pentagon.

Answer 3

1. You are incorrect. The heaviest parts of the plane (engines, e.g.) did in fact penetrate the entire WTC and exit the opposite side. Further, the core of the WTC was reinforced concrete; only the skins were glass and steel.

2. How do you know how long it took to collapse? The collapse of the bottom portions was completely hidden by dust & smoke, and utterly invisible in any video I've seen. Further, the bottom portions can indeed collapse long before the floor immediately above, because the impacts of upper floor collapses are greater than any individual floor can stand. You can drive a nail with a hammer just as easily even if there is a steel bar between the hammer and the nail.

3. Gravity points downwards, but dynamic couples introduce rotations in the collapse that can result in debris going in any random direction.

Answer 4

Please

1. There are so many factors that affect the penetration of something like a plane into something like a building that NOBODY could get a handle on them and accurately predict penetration even if they had good information about the speed of the plane and all the structural stuff.

2. The building collapse is on film so the timing is known. The THEORY of "progressive collapse" is even more difficult to apply than the penetration calculation. There is no way to verify the theory or model meaningfully.

3. I just sat on a stool at my house. I went down, along the gravity gradient, some pieces of the stools leg launched sideways and even up. This surprised nobody.

The implied point here is that these towers collapsed due to some cause other than the large jet planes that flew into them. This is a huge stretch for anyone with a "scientific background".

Have your heard of occam's razor?
Think about it!

Answer 5

could the fall rate have anything to do with fire weakening the building?

how about angle of entry?

those things that flew out of the building did fall, they were projected laterally first because of the swoosh of air caused by the fall of the building.

im sorry, i dont know much about physics, so this may not be as much help as you need.