Free fall again

[EternalSceptic]

Warning: I have a very limited internet access and therefore it is hard for me to seach for the exact official values, so the values below are just estimates and may be off by a significant amount. I would appreciate corrections. Thank you.

1)
Did I miss something or are all the time calculations for free fall slightly wrong?
They all calculate the time of free fall from the height of of the roof of the towers, but it was a complete block of all the floors above the impact point which started to fall when the collapse began. Therefore the free fall time would be less than that of a stone dropped from the roof.

Assuming a height of 411m (the height of the roof) I get a free fall time of
t = sqrt(2s / b) = sqrt(822 / 9.81) = sqrt(83.79) = 9.153 seconds

I don't have the exact height of the impact point at hand, so I estimate (from the videos) 350 meters. In this case I get
t = sqrt(2s / b) = sqrt(700 / 9.81) = sqrt(71.36) = 8.45 seconds

Which makes the "near free fall" time a little less than near.

2)
As soon as the floor where the impact occurred was weakened enough, the block above the impact point started to come down. The height of one storey is about 4 meters and the weight of the block about 50 000 tons. If I assume, that half of the potential energy of this block was used up to destroy the structure of this storey the average acceleration is about 5 m per second sqare. In this case the upper block would impact the top of the next lower storey at a speed of
v = 5 * sqrt(8 / 5) = 5 * sqrt(1.6) = 5 * 1.264 = 6,324 meters per second after 1.264 seconds.

A mass of roughly 50000 tons impacting at more than 22 kilometers per hour must have acted as a giant hammer, not only destroying the storey where it hit, but also sending enormous shockwaves down the whole building, and I cannot imagine, that these shockwaves left the structure below totally intact. At the same time the falling block acted as a giant piston compressing the air below and causing the air to rush out sidewards at enormous speeds, which became higher at each destroyed storey. When you have ever seen what a tornado can do to a house you can imagine what this compressed air could do to all material which had been broken loose.

3) and last
The argument, that a rather weak structure like an airplane cannot destroy steel columns again lets me think of a tornado. A tornado is just moving air, but it can completely destroy houses and, as I have heard (please correct me if I am wong) even press straw deep into much harder matter like wood. I cannot see any reason why a nearly 200 tons airplane could not cause the destruction we can see in the videos. Given the poor quality of the videos I have seen I think it is impossible to draw conclusions from single frames around the impact which happened at a speed of near 300 meters per second. both the resolution and the frame timing are ways too coarse.

Opinions?

 

[AZCat]

Not quite. The material of which the top floors are composed of still has to drop the full height down to the ground. Unless it is under an additional accelerating force, it cannot reach the ground faster than the value calculated in your first equation.

It is important to recognize the "moving block" of floors when considering momentum, though - something Dr. Wood failed to do in her "billiard balls" model (among other things).

 

[A W Smith]

Not quite. The material of which the top floors are composed of still has to drop the full height down to the ground. Unless it is under an additional accelerating force, it cannot reach the ground faster than the value calculated in your first equation.

It is important to recognize the "moving block" of floors when considering momentum, though - something Dr. Wood failed to do in her "billiard balls" model (among other things).

In all likelihood the debris from the initiating crush zone would hit the ground first.

 

[EternalSceptic]

Not quite. The material of which the top floors are composed of still has to drop the full height down to the ground. Unless it is under an additional accelerating force, it cannot reach the ground faster than the value calculated in your first equation.

It is important to recognize the "moving block" of floors when considering momentum, though - something Dr. Wood failed to do in her "billiard balls" model (among other things).

You are right of course - somehow I was always thinking about the time until the block reached the ground as the fall time.

The billard ball model is of course faulty, alone because if the upper block had really stopped after coming down one floor then the whole collapse would have stopped except in a case where the structure of the lower building would have been damaged to a point where it just could withstand the impact for fractions of a second. To my eyes the videos do not show a big deceleration after the block has smashed the first floor on it's way down.

I'd recommend a cheap and simple experiment to dr. Wood:
Gently put a hammer on your foot.
Notice the feeling.
Now call the ambulance and wait until they approach your door.
Then lift the hammer up above your head, which is about 2 meters - half the height of a WTC storey - and let it drop down on your foot.
Notice the feeling and compare it to the first one.
The ambulance people will take care of the rest.

 

[R.Mackey]

You might enjoy the very simple energy argument I put forth here.

One thing I've always struggled with is that the end of the collapse isn't really well-defined, and was shrouded in an enormous cloud of choking thick dust. So trying to pin it down to the second doesn't make much sense to begin with. This is part of why the Idiot Movement can never make up its mind whether it stops the clock when the upper block touches the ground (the Pile, actually), or when the roof gets there.

 

[EternalSceptic]

In all likelihood the debris from the initiating crush zone would hit the ground first.

Most of it, at least. Part of it may have been blown or pushed upwards, but I think this will bw a neglegible amount.

 

[EternalSceptic]

You might enjoy the very simple energy argument I put forth here.

I did already (and appreciated it), shortly after you posted it.

One thing I've always struggled with is that the end of the collapse isn't really well-defined, and was shrouded in an enormous cloud of choking thick dust. So trying to pin it down to the second doesn't make much sense to begin with. This is part of why the Idiot Movement can never make up its mind whether it stops the clock when the upper block touches the ground (the Pile, actually), or when the roof gets there.

.

That's a point, yes. But it should have no influence on the CD - theory, because this theory affects mainly the part of the building below the impact point. (IMHO)

 

[gumboot]

I did some calculations of the impact forces involved in the collapse.

By my calculations, the impact force increased by about 3 GJ between hitting the first intact floor and hitting the second. This essentially means if it can be demonstrated that a WTC floor truss is incapable of sustaining a 3 GJ impact intact, there is no way the structure could have arrested the collapse once initiated.

It would be interesting to see some study into what sort of impact force those floor trusses could sustain.

-Gumboot

 

[westprog]

You might enjoy the very simple energy argument I put forth here.

One thing I've always struggled with is that the end of the collapse isn't really well-defined, and was shrouded in an enormous cloud of choking thick dust. So trying to pin it down to the second doesn't make much sense to begin with. This is part of why the Idiot Movement can never make up its mind whether it stops the clock when the upper block touches the ground (the Pile, actually), or when the roof gets there.

It should, however, be possible to calculate the speed of collapse from a fixed camera point.

Mark the lowest point visible behind the debris. When the top of the building passes that point, note the time. The distance travelled can be calculated by counting floors.

The time the building takes to hit the ground is impossible to estimate, but the time the top of the building takes to travel down a certain distance can be calculated. I'm not aware that anyone has done so. I wouldn't trust the CT calculations, of course.

 

[EternalSceptic]

It should, however, be possible to calculate the speed of collapse from a fixed camera point.

Mark the lowest point visible behind the debris. When the top of the building passes that point, note the time. The distance travelled can be calculated by counting floors.

The time the building takes to hit the ground is impossible to estimate, but the time the top of the building takes to travel down a certain distance can be calculated. I'm not aware that anyone has done so. I wouldn't trust the CT calculations, of course.

I think an estimate of the time until the upper block hits the pile scould be fairly accurate if we just measure the acceleration of the upper block during the visible part of its way down. With each destroyed storey the falling mass increases and the lower rest of the building becomes weaker, so we will arrive at a slightly longer total time, but the difference shouldn't be big enough to make a significant difference if the visible part of the fall happens not too far away from free fall speed.

Is there a sound recording of the collapse available? It is just my guess, but I think the moment when the upper block hits the pile and starts to disintegrate should be audible as a noticable change in the noise. A recording of the seismic waves if available should also help.

Of course the upper block will also have partly disintegrated during the fall, but much less because all the debris produced will have an effect mainly on the lower part of the building and probably acted as sort of a buffer between the upper and lower block.

Analysis or all these data should give us a pretty accurate time value.

 

[Mancman]

Is there a sound recording of the collapse available? It is just my guess, but I think the moment when the upper block hits the pile and starts to disintegrate should be audible as a noticable change in the noise. A recording of the seismic waves if available should also help.

Of course the upper block will also have partly disintegrated during the fall, but much less because all the debris produced will have an effect mainly on the lower part of the building and probably acted as sort of a buffer between the upper and lower block.

Analysis or all these data should give us a pretty accurate time value.

This isn't very scientific, but in this video:


..you hear a noticeable 'thump' sound at the 14 second mark. Could well be the upper mass hitting the ground/basement levels.

 

[gumboot]

I doubt there was much left of the upper floors by the time they hit the ground - the lower core would have torn it to shreds... Imagine falling face first into a tightly packed cluster of steel stakes.

-Gumboot

 

[Mancman]

I doubt there was much left of the upper floors by the time they hit the ground - the lower core would have torn it to shreds... Imagine falling face first into a tightly packed cluster of steel stakes.

-Gumboot

Perhaps the sound is the impact of the floorslabs? They would have compacted during the collapse and hit the ground essentially as one big crushed mass, weighing 100,000+ tons and travelling at over 100mph. Perhaps.

Don't forget that a huge piece of the WTC2 core stood for a few seconds after the collapse.

 

[gumboot]

A good chunk of both cores were still standing after each building collapse. The core section of WTC1 was at least half the overall height.

-Gumboot

 

[Mancman]

A good chunk of both cores were still standing after each building collapse. The core section of WTC1 was at least half the overall height.

-Gumboot

Yeah, I know. I was only reffering to the tower in the video.

(N.B I edited out the sentence about the cores just after posting, as I realised it wasn't massively relevant, I'll edit it back in so the thread flows properly)

 

[EternalSceptic]

I doubt there was much left of the upper floors by the time they hit the ground - the lower core would have torn it to shreds... Imagine falling face first into a tightly packed cluster of steel stakes.

-Gumboot

Well, gumboot, I am not sure of that. The falling upper block smashed stories below and their mass is added to the force which hit the lower storeys, (and sort of a buffer) so an increasing amount of debris was available to destroy lower floors with decreasing influence of the upper block. The videos I have seen do not show excessive destruction of the upper block until it disappears in the cloud of dust and debris. Of course there will be some destruction to the upper block, but I think some percentage will hit the pile undestroyed.

I may be wrong in this, but I hope this could be a subject of further fruitful discussions.


Robert

 

[PhantomWolf]

I have a very limited internet access and therefore it is hard for me to seach for the exact official values, so the values below are just estimates and may be off by a significant amount.

The first panels hit the ground approximately 9 seconds after collaspe started in WTC 2 and 10 sec for WTC 1. Global collapse took between 16 and 17 seconds for WTC 2 and 18 to 19 seconds for WTC 1.

 

[EternalSceptic]

The first panels hit the ground approximately 9 seconds after collaspe started in WTC 2 and 10 sec for WTC 1. Global collapse took between 16 and 17 seconds for WTC 2 and 18 to 19 seconds for WTC 1.

If you mean with "first panels" parts of the debris ejected at the start of the collapse that is exactly wa I was estimating. I am totally convinced that the collapse happend normally as a result of the impact and the following fires. What I want to get here is an a detailled as possible and as much as possible supported by available evidence timeline of what happened. Maybe this will convince _a few_ of the troothers.