"Freefall"

[GlennB]

Various reasons I've seen revolve around destroying federal documents stored in the building or destroying Guliani's "bunker" to eliminate evidence that the attacks were staged and controlled from there.

And this would be the plan of all plans....

Control the Twin Towers CD from a building that's likely to get smashed by many flying steel girders, while all along you're sitting on vast amounts of explosives.
That's got my vote. Oh yes.

 

[GlennB]

One thing is sure, it falls because the things that hold it up cannot longer hold it up.

Leave the Dark Side, einsteen. You know you want to.

 

[defaultdotxbe]

Wouldn't it have been easier to just break out the shredder.

this is a good point, because demolishing a building isnt a good way to destroy evidence, papers from the WTC rained down on the streets after the collapse, they found legible paper in the rubble, they were able to reconstruct computer records of trades made at the WTC

now if they really wanted to destroy evidence in WTC7 they should have just left the fires burning for a few days

 

[Class]

Wouldn't it have been easier to just break out the shredder.

No, because once you shred all the documents,you need to demolish the building to destroy the shredder.

 

[einsteen]

yes, I got that wrong, I was misled by a paper of someone called Kutla or Kutta and he calculated 8.3 which is near 8.2 for the total time. But NIST's times are before the global collapse. But that internal pre-collapse that happens is of course related with the destroying of the inner structure.

 

[Horatius]

And this would be the plan of all plans....

Control the Twin Towers CD from a building that's likely to get smashed by many flying steel girders, while all along you're sitting on vast amounts of explosives.
That's got my vote. Oh yes.

Hey, come on, if these plotters were smart, they wouldn't have left all this great video evidence lying around!

 

[Gravy]

this is a good point, because demolishing a building isnt a good way to destroy evidence, papers from the WTC rained down on the streets after the collapse, they found legible paper in the rubble, they were able to reconstruct computer records of trades made at the WTC

now if they really wanted to destroy evidence in WTC7 they should have just left the fires burning for a few days

Yes, and they also recovered hundreds of hard drives with usable information from the rubble. Somebody should have shredded them.

 

[MRC_Hans]

Yes, and they also recovered hundreds of hard drives with usable information from the rubble. Somebody should have shredded them.

Really? I thought TS123½ said it was all reduced to a fine powder?

Hans

 

[Gravy]

Really? I thought TS123½ said it was all reduced to a fine powder?

Hans

Don't you remember? Hard drives in 2001 were mostly less than 60 microns in size. That was before the computer companies adopted the "large type" ones and zeros as the bit standard.

 

[CurtC]

Maybe they pieced together the 60-micron powder to reconstruct the drives. Compared to the rest of the 9/11 conspiracy scenario, like hydrogen bombs and hologram planes, that sounds almost plausible.

 

[Hellbound]

No one has really brought it up, but I'd like to point out a common misconception, as well, using a hypothetical scenario.

An object falls 490m. it takes 11 seconds to fall this far.

Freefall speed would be 10 seconds.

So, what is the percent difference in acceleration?

The Loosers seem to think that 10 seconds would be "almost freefall" in this scenario. The math is a bit different, though.

d = distance (meters) = 490m (in this scenario)
v₀ = initial velocity = 0 m/s
t = time (10 seconds, for this hypothetical)
a = acceleration = what we're looking for

d = v_ot + 1/2 at²490m = 1/2 * a * (11s)²490m = 1/2 * a * 121s²490m = 60.5s² * a
490m/60.5s² = a
8.10 m/s² = a

8.10m/s²/9.8m/s² = 82.6%

1 second (from 11 to 10) is almost 18% less acceleration, which means 18% less energy. THe same thing can be done with the various times for the WTC towers, and you can use this to determine what percent of the potential energy went into breaking the structure and/or throwing debris, and what to falling. Basically, there's a simpler way to figure this:

(Freefall Time/Actual Fall Time)² = % of "freefall" acceleration. The rest of the difference between this and freefall is energy available for the rest of the sturcture.

So, let's take WTC 7. We have an actual freefall time of 5.95s. The claim is that it fell in 6.5 seconds. THat gives us a figure of 83.8% of freefall speed. Again, about 16% of the potential energy available for damage to the structure.

Looks a bit different once the math is done, right?

 

[einsteen]

Glad you notice later that your 82.6% is nothing more than (10/11)^2
Your energy argument doesn't work however, it's no simple matter of one minus the rest,
you should have a model first and then work it out, that isn't simpel.
And there is in fact no potential energy available to break the structure because
it should first be transformed into kinetic energy. In the twin towers it is assumed
the block falls 3.7 meter first and then a fraction of it is used to break the structure
and so on, If there is no initial speed this cannot happen. The twin towers would
stand forever if there was no initial helping hand. A column of steel can never
collapse because of its own weight. The internal forces in matter (electromagnetic in fact) are
much stronger than gravity when we talk about buildings etc. The shockwave in wtc7 is a high
energy impuls, needed to damage the structure. You can understand that because at that moment
it is stil standing and the potential energy is still available, but then it goes down.
The percentage of freefall acceleration or how you want to call it is due to the fact that it is
no intact building that falls because a trap-door is opened, but because al mass want to move
to the bottom and there is some internal resistance.

 

[MRC_Hans]

And there is in fact no potential energy available to break the structure because it should first be transformed into kinetic energy.

Really?? So if I place weights on a table, I can place as heavy weights as I please, because since there is no kinetic energy to break the legs, it will hold up forever?

Are you sure you didn't miss a bit here?

In the twin towers it is assumed the block falls 3.7 meter first and then a fraction of it is used to break the structure and so on, If there is no initial speed this cannot happen. The twin towers would stand forever if there was no initial helping hand.

They would keep standing, no matter how much the supporting structure was weakened? Are you serious???

A column of steel can never collapse because of its own weight.

On which planet does this apply? Are you crazy or something?

The internal forces in matter (electromagnetic in fact) are much stronger than gravity when we talk about buildings etc.

We should certainly hope so, otherwise all buildings would fall down. What if those internal forces are weakend by something, however? Like by heat?

The shockwave in wtc7 is a high energy impuls, needed to damage the structure.

That and some fire, ehhh? So, now the structure is damaged, according you what you say above, it should still have no problem holding up the weight of the building?? No matter how much it is damaged???

You can understand that because at that moment it is stil standing and the potential energy is still available, but then it goes down.
The percentage of freefall acceleration or how you want to call it is due to the fact that it is no intact building that falls because a trap-door is opened, but because al mass want to move to the bottom and there is some internal resistance.

What are you trying to say by this?

Hans

 

[GlennB]

.... The twin towers would stand forever if there was no initial helping hand. A column of steel can never collapse because of its own weight.....

What about if it has 2,000 tonnes to support, a fire to soften it and expanding horizontal girders to give a push inwards?

 

[einsteen]

@MRC_Hans

Let’s not compare apples with oranges, I mean an object that is able to carry itself cannot break spontaneously because of potential energy. Your table example is true of course but as you already proof in your own example you add external forces by adding heavy weights. In this case I was referring to wtc7, the immense building with the steel frame. There is no way this can crush spontaneously, energy should be added, that doesn’t come from potential energy because it is still standing before it collapses. A little bit fire in wtc7 will not weaken the steel and certainly not crush it. Steel is a excellent heat conductor, think about your cooking pan. The damage is far more important than the heat. What would happen if you break a leg of the Eiffel-tower or maybe two or maybe three?

The twin towers would stand indeed if there was no initial high-speed motion. The energy to break a floor (our old friend Greening, I’m a big fan of Greening and that is no joke) comes from the kinetic energy, only a fraction is assumed to be used to break the floor and everything else. I’m serious; if that initial speed was not there it would stand forever.

What I wanted to say with your last quote is that Huntsman difference in acceleration has only to do with a loose bulk of mass falling down and his energy argument has no meaning.

@GlennB

I don’t accept the whole steel frame became weak and if it did then it would be a continuous process. It’s so completely odd that the block at t=0 can move freely a distance of 3.7m. Greening admits this cannot be proved.

 

[twinstead]

Einsteen, I'm no expert, but there are SO many qualified structural engineers who disagree with you.

This troubles me. What makes them so wrong and you so right?

 

[einsteen]

That's a good point, at this stage I then should stop and keep my mouth because I surely know my limitations.

(begin CT'er mode)

Assumptions1 -> results1 -> consistent with reality
Assumptions2 -> results2 -> not consistent with reality

hence let's use Assumptions1. The reports are still true and scientific under the specific assumptions

(end CT'er mode)

 

[MRC_Hans]

@MRC_Hans

Let’s not compare apples with oranges, I mean an object that is able to carry itself cannot break spontaneously because of potential energy.

Ehhr, no. Not as long as it is defined by "being able to support itself", but that is circular. The point is that a structure can break, not because of potential energy, but because of the forces acting on it, if it is weakened sufficiently.

Your table example is true of course but as you already proof in your own example you add external forces by adding heavy weights.

No problem. Just for you, I'll saw into the legs instead.

In this case I was referring to wtc7, the immense building with the steel frame. There is no way this can crush spontaneously, energy should be added, that doesn’t come from potential energy because it is still standing before it collapses.

No energy needs to be added. Structural strength needs to be taken away. Obviously, this will take some energy, but not some that needs to take direct part in the collapse.

A little bit fire in wtc7 will not weaken the steel and certainly not crush it.

How about a LOT of fire? And extensive direct structural damage.

Steel is a excellent heat conductor, think about your cooking pan.

I'm quite sure you know better than this, because that is primary school physics: Iron (and thus, steel), is an extremely poor heat conductor as metals go. This is the reason you can hold a steel rod in your hand while it is red-hot in the other end. Try that with copper .

The damage is far more important than the heat.

No. If the damage was most important, WTC 7 would have collapsed shortly after sustaining structural damage.

What would happen if you break a leg of the Eiffel-tower or maybe two or maybe three?

What do you think would happen?

The twin towers would stand indeed if there was no initial high-speed motion. The energy to break a floor (our old friend Greening, I’m a big fan of Greening and that is no joke) comes from the kinetic energy, only a fraction is assumed to be used to break the floor and everything else. I’m serious; if that initial speed was not there it would stand forever.

You may be serious, but you remain wrong. A building stands as long as its structure is strong enough to withstand the force of gravity acting on its weight. If you start weakening the structure, the moment you reach the point where it can no longer support the weight, the building collapses. No need for any kinetic energy.

BTW, I hope you are aware that you are arguing that demolitions are impossible?

What I wanted to say with your last quote is that Huntsman difference in acceleration has only to do with a loose bulk of mass falling down and his energy argument has no meaning.

I know. You are wrong.

I don’t accept the whole steel frame became weak and if it did then it would be a continuous process.

It was a continuous process. The frame was continuously weakened. At the point where it became weaker than the force acting on it, it gave way, the building above it started to move downwards, and then kinetics took over.

It’s so completely odd that the block at t=0 can move freely a distance of 3.7m.

At t=0? At t=0, it started moving, because its support failed. When it had moved 3.7m, it had accelerated somewhat and impacted on the structure below.

I think you are being deliberately obtuse, here. If a structure supporting a weight is being weakened, there will come a point when it can no longer support that weight. What will, in your opinion, happen then?

Hans

 

[einsteen]

Dear Hans, steel and copper are good heat conductors. Copper better than steel but steel is a very good heat conductor.

I would expect the Eiffel tower would topple, that's also what the controlled demolition experts do.

Ok Hans, wtc7 was damaged from the beginning and the heat made it weak, after a certain point everything broke inside ? maybe I should put my books out of the dust but I've never heard about this effect.

 

[MG1962]

The twin towers would stand indeed if there was no initial high-speed motion. The energy to break a floor (our old friend Greening, I’m a big fan of Greening and that is no joke) comes from the kinetic energy, only a fraction is assumed to be used to break the floor and everything else. I’m serious; if that initial speed was not there it would stand forever.

What is being forgotten is load bearing. Each floor of the tower was rated at 1100 tons. Once the load on that floor exceeds that level, it will break. That is the whole point of progressive and pan cake collapses. As a floor gives way, the floor below tries to take up the load, snaps, then the next floor and so on. The process gathers speed as it continues. The rubble from above is accellerating, and the demand on the surviving floors is becoming greater with each moment