Freefall?

[Dave Rogers]

3. The link provided here about the 15 second collapse includes the following vital assumption which is missing in this thread: "Resistance from the structure is zero. As in, there are no vertical columns, and no assembly connections. (point 4 in link) This supports the claim intended by the author.

I'd like just to address this one, if that's OK with you. There are two points I'd like to make in response.

Firstly, assumption 7 is that 30% of the mass of each floor is ejected in each impact. This is referred to as a conservative assumption, but without a rigorous justification. It is commented that this only increases the collapse time by 1 second, which is an indication of how insensitive the collapse time can be to relatively large changes in the assumed conditions. Removing 30% of the mass at each collision will remove something like 25% of the mass of the building, and therefore 25% of the potential energy (slightly less, actually, as the top floors are assumed to remain intact). Greening (http://www.911myths.com/WTCREPORT.pdf) estimates fracture energies of approximately 1e9 joules per floor, with a total energy from collapse of 1e12 joules; the energy required to crush each floor support is of order 10% of the potential energy generated in one floor's collapse. Clearly, if the assumption of 30% loss of mass at each collision is high, there is therefore more than enough energy available to crush the supports.

Secondly, Greening, in the above paper, calculates collapse times based firstly on momentum transfer alone, and then on momentum transfer plus the floor collapse energy. The difference between the two is found to be less than 1 second in total collapse time, even when the energy requirement for floor collapse is doubled from the initial estimate. Therefore, if you accept the papers assertions (momentum transfer calculation of a 14 second predicted fall time and actual observation of a 15 second fall time), the paper in fact proves that pancake collapse can account very accurately for the observed collapse time of the towers.

In conclusion, therefore, the paper you refer to offers no proof that pancaking is impossible; on the contrary, it provides a model of the collapse which agrees with the observed collapse to well within the uncertainties of the measured collapse time.

I suggest you read Greening's paper, and Greening and Ross's debates following on from it. If you understand the issues in these you will be well equipped to debate the collapse time.

Dave

 

[programmer]

Thanks for pointing this paper out. I will spend some free time in reading this paper and the critics/reviews about it. I am no expert but i can understand math and basic physics. I've been reading lately lots of claims going for and against the official explanations, and I want to basically establish if the official version is plausible or not before considering anything else.

 

[Darth Rotor]

As RWGuinn would put it thanks for the Freefall101.

Your application of terminal velocity is frankly over elaborate and just bored me but, for future reference the value of g for the New York area is 9.802 m/s^2

http://www.internationalskeptics.com/forums/showpost.php?p=2099718&postcount=7551

To three significant digits, 9.8 works for the purpose of discussing times rounded to seconds, which is as much precision as the video evidence warrants.

Sorry to bore you.

DR

 

[beachnut]

Hi, I am new to this forum.
I would like to address some of the topics of this thread, hopefully you will consider them objective.

1. About the claim "faster than the speed of gravity": This certainly is a wrong representation of the whole picture, as it can be seen that the mayority of the mass takes about 15 seconds to complete the collapse. However, it would be very important if somebody measures the speed of the initial collapse (i.e first seconds) and prove that it was not faster than gravity.
2. As some of you pointed out, gravity provokes acceleration, not speed. However, there is a fixed speed increase associated with gravity.
3. The link provided here about the 15 second collapse includes the following vital assumption which is missing in this thread: "Resistance from the structure is zero. As in, there are no vertical columns, and no assembly connections. (point 4 in link) This supports the claim intended by the author.
4. I googled a little on Dr. Judy Woods and cannot find a reference to dentistry, can anybody here please provide this? Thanks.
- What I found is her bio: janedoe0911.tripod.com/Wood_Bio.html
- Found a paper at VirginiaTech about steel: scholar.lib.vt.edu/theses/available/etd-06072006-124140/

Please debate

1. proved! gravity acts, as it is theorized, at the speed of light. No the top fell as it failed at an acceleration of 9.8 m/s*s, but modulated by any thing in the way. (you must be seeing the first modulated speed of the collapse as the first section fall a few meters and instantaneously collapse the next thing in the way it seems to slow down, it kind of does but never stops, until the ground). Easy proof. There were no booster rockets on the roof, no beam weapon pushing, just gravity. What makes anyone think the first second was faster than gravity; yet you mean just falling. It was slower than a free fall. You are not familiar with gravity are you? Unless you come up with facts and evidence to prove there was some extra force in the down direction you must be using the old opinionFact machine of CT land.
2. That is called acceleration.
3. No the building could collapse with resistance, it would not have to take 15 seconds. If you do some energy modeling, you will find a 10 percent or less than 20 percent resistance penalty due to building failure, then acceleration and momentum transfer. You may be like most and ignore the ever growing mass joining the accelerations to the ground.
4. Judy Woods appears to be insane – her latest brain wave theory is a beam weapon did it and like some Moody Blues frequency only vaporized/dustified the steel. ~She was fired for not teaching her subject but ~ranting about the WTC. Her momentum work would be an F – her "dustification" puts her in a whole different class of folk; sunny brooks comes to mind, but after a coma for years, what can you expect from a woo?.

The first seconds would be where you would see the most effect from the first moving mass destroying other parts of the building. That is what you mean, the first section seems to takeoff fast and slow down. If you see that, it is the resistance of destroying the next section. This modulation can be heard on 9/11 during the first collapse.

 

[PhantomWolf]

prove that it was not faster than gravity.

Gravity travels at the speed of light.

The building clearly did not collapse at the speed of light.

Thus the building collaspe was slower then Gravity. Q.E.D.

eta: Darn, beaten to the punch by 10mins

 

[rwguinn]

Gravity travels at the speed of light.

The building clearly did not collapse at the speed of light.

Thus the building collaspe was slower then Gravity. Q.E.D.

eta: Darn, beaten to the punch by 10mins

BZZZT!
If you look at the equation [latex]F=%20G*M1*m2/r^2[/latex]
there is no "time" dimension....It is instantaneous

 

[PhantomWolf]

there is no "time" dimension....It is instantaneous

That post really needs a smilie. Where I come from, some people are likely to declare that and be serious.

 

[rwguinn]

That post really needs a smilie. Where I come from, some people are likely to declare that and be serious.

I worked for NASA as a coop in my college days, and on STS payloads for 18 years. See your sig for the correct attitude--it fits NASA to a "T"
And the units in that equation are mq=kg, m2=kg, r=m, G=N*m/kg^2
See a seconds in there anywhere?...
Just because N = kg*m/sec^2, you have to know that. If you insist on metric units, there is no evidence of time.
That's what you get for naming a bunch of units after dead people, instead of leaving them alone...

 

[programmer]

Gravity travels at the speed of light.

That is certainly not in question, unless of course you want to debate gravitons . Again what is meant is the speed of the collapse wave (as a ratio between distance traveled and time ellapsed) like this:
x = 0.5 g t^2 => t = (2x/g)^0.5 for a given distance x of the collapse wave. So if we take the video from beginning of the collapse, given a time ellapsed tf (say 5 seconds) we can compare the calculated distance xf with the actual distance travelled by the collapse wave, and THEN we can tell for sure the fall was not "faster than (allowed by) gravity".

You are not familiar with gravity are you? Unless you come up with facts and evidence to prove there was some extra force in the down direction you must be using the old opinionFact machine of CT land

Actually I have not made any claim about some extra force. I raised a question about IF the initial collapse sequence could be faster than allowed by gravity. I don't know, so that's why I asked for demonstration, if anyone here knows where I can find one, please point it out, else I will try to measure the acceleration myself, as described above.

3. No the building could collapse with resistance, it would not have to take 15 seconds. If you do some energy modeling, you will find a 10 percent or less than 20 percent resistance penalty due to building failure, then acceleration and momentum transfer.

Sounds interesting, you got a source for that calculation? Thanks.
Btw reading Greening's paper will take me a while, not so much free time for me these days

 

[R.Mackey]

I put together a much simpler, energy-based derivation of the collapse time as a function of energy absorbed here. This should not be treated as a substitute for Dr. Greening's carefully written analysis, but it may be easier to understand.

What it shows relevant to your question is that the collapse time is expected to be between 10 and 20 seconds for virtually any amount of energy input. Small losses over the side would not change the collapse time more than perhaps a second, which is within measurement error given the huge billows of smoke and dust. And huge losses over the sides (not supported by video) that slowed the collapse more than this would be more likely to halt the collapse entirely.

 

[Panoply_Prefect]

Am I just grossly oversimplifying things here, but doesnt the fact that the debris fall faster than the building itself, debunk the "free fall" and "faster than free fall" theory? Is there any scenario where a building in free fall would have debris falling faster?

/S

 

[JimBenArm]

Am I just grossly oversimplifying things here, but doesnt the fact that the debris fall faster than the building itself, debunk the "free fall" and "faster than free fall" theory? Is there any scenario where a building in free fall would have debris falling faster?

/S

Well, if you want to stick to the real world, yes. But you forget we're in CT World, where all that mathy, logical stuff gets thrown out.

 

[Panoply_Prefect]

Well, if you want to stick to the real world, yes. But you forget we're in CT World, where all that mathy, logical stuff gets thrown out.

I just dont understand how this theory, or what you want to call it, got so widespread. Has any CD ever jettisoned clouds of dust so they accelerate faster than freefall?

/S

 

[William Rea]

To three significant digits, 9.8 works for the purpose of discussing times rounded to seconds, which is as much precision as the video evidence warrants.

Sorry to bore you.

DR

No problem.

 

[William Rea]

I worked for NASA as a coop in my college days, and on STS payloads for 18 years. See your sig for the correct attitude--it fits NASA to a "T"
And the units in that equation are mq=kg, m2=kg, r=m, G=N*m/kg^2
See a seconds in there anywhere?...
Just because N = kg*m/sec^2, you have to know that. If you insist on metric units, there is no evidence of time.
That's what you get for naming a bunch of units after dead people, instead of leaving them alone...

Could you offer further explanation of what you mean here?

 

[ryanebelhar]

the enire WTC/freefall/CD talk reminds me of the episode of the Simpsons when Burn's Casion was demolished

All the characters are watching as the casino is preparing to be demolished.

Demolitioner #1: Five, four, three, two ...
Bart: All right! Here comes the implosion!
Demolitioner #2: Implosion? But I thought you said ...

 

[Gravy]

267 hits on Google isn't terribly impressive is it.

William, you protested about another poster using one example:

OK, just doing a quick calculation and adding it up bear with me...(tapping noises from keys on spreadsheet)...Hmm yeah, OK, I make that a total of one source quoted! I can't believe that because it wouldn't be like you guys to take one snippet of information and use that as a basis to debunk the whole set of data would it

In ten seconds, I provided 267 more examples than you could muster. To you, that is insignificant. That's your problem.

Here is my challenge to you, William Rea:

You seem to do nothing but complain about the methods used by "skeptics" on these forums. Yet you never demonstrate what us "skeptics" get wrong.

So start a thread and produce your BEST EVIDENCE that the official version of the 9/11 attacks is wrong.

Give us your very best evidence, William. Are you up to it?

I say you're not.

 

[pagan]

The 9/11 CTers are always going on about how the WTC collapsed "faster than freefall". Have any of them ever proven this? That is, told us the speed of a object free-falling through the air, and then told us the precise speed of fall of the WTC?

I've never seen any truther claim that the towers fell faster than free fall.

The term usually used is that the towers virtually fell in free fall speed. One of our best arguments and a sure sign for the use of explosives.

Anyway, this is hair splitting. You guys are getting desperate.

 

[A W Smith]

Pagan have you not seen mine (1)and Gravys(267) posts with such claims?



and
At the time i posted I only had time for one example. My wife had served me dinner and was growing impatient.

 

[Cl1mh4224rd]

I just dont understand how this theory, or what you want to call it, got so widespread.

Repetition, pure and simple.