9/11

stignasty · May 3, 2007

What does a force look like in your imagination ?

It looks like this.

PolyNewbie · May 3, 2007

Riverwind:This means the normal force exterted on #4 _must_ be equal to the weight of the load.

That never ever happens - not even for an instant.

Riverwind · May 3, 2007

If 2 and 3 acted as pivot points, I cannot see this. There would be a negative stress on the 4th corner.

You are correct up until the point when 2&3 collapse. At that point the forces of the system immediately redistribute to find a new equilibrium - just like they redistributed to 2&3 after leg 1 collapsed.

Consider a situation with light table top and a strong leg that is attached to the floor. The table top would remain suspended in the air and the full weight after legs 2&3 disappeared. There would be no rotation and no collapse and leg 4 would have the full weight of the table top pushing down on it.

A system with a heavy table top would not behave any differently immediately after legs 2&3 collapse. Top _cannot_ move until something breaks or bends. What happens next depends on what breaks/bends faster.

If the leg breaks faster then the table collapse straight down.

If the connection to the floor breaks faster the table topples over.

In this example, the table leg is completely overloaded which means there it could never bend before it collapsed. It is a phsysically impossibility.

PolyNewbie · May 3, 2007

Riverwind:At that point the forces of the system immediately redistribute to find a new equilibrium - just like they redistributed to 2&3 after leg 1 collapsed.

Oh, OK. I get it now. You think the table is in equilibrium due to a single force normal to the leg supporting it while being supported by the one leg. Thats is why you think the forth leg would hold the weight of the table or it would collapse straight down.

If the leg doesn't fail and the table stays up then the load of the table is brought down on that one leg, but it is not a simple normal force as you describe. Some of the vertical sections of the leg will be in tension and the other part will be in compression. So there is no single "normal force". the sum of these forces would be a normal force but it would be a meaningless summation because not all of the forces act on the same point in space - ie the summation would lead to an incorrect conclusion like adding 3 oranges to 2 apples and saying you have 5 oranges.

Think of how your arm would feel if you were holding the table up from one corner with one hand - would it feel the same as if your were holding a barbell up weighing the same as the table top ? How would the table top react as you run out of strength ?

None of your physics makes sense - its all wrong, but you had me confused with this whole table leg attached to the floor thing. Anyways your conclusions are all wrong even with that assumption being brought in when the leg fails and when the leg does not fail. (in both cases you are all wrong)

I take then that if the wtc buildings were supported by only one support column at one of the corners and all of the other supports were broken and that single support somehow failed that the building would fall straight down. Is this correct ?

Why can't you tell us what kind of engineer you are ? I'm really really curious.

Figleaf · May 4, 2007

If 2 and 3 acted as pivot points, I cannot see this. There would be a negative stress on the 4th corner.
You are correct up until the point when 2&3 collapse. At that point the forces of the system immediately redistribute to find a new equilibrium - just like they redistributed to 2&3 after leg 1 collapsed.
Consider a situation with light table top and a strong leg that is attached to the floor. The table top would remain suspended in the air and the full weight after legs 2&3 disappeared. There would be no rotation and no collapse and leg 4 would have the full weight of the table top pushing down on it.

A system with a heavy table top would not behave any differently immediately after legs 2&3 collapse. Top _cannot_ move until something breaks or bends. What happens next depends on what breaks/bends faster.

If the leg breaks faster then the table collapse straight down.

If the connection to the floor breaks faster the table topples over.

In this example, the table leg is completely overloaded which means there it could never bend before it collapsed. It is a phsysically impossibility.

Your example does not represent what really happens -- Take your one legged table with the top supported at one corner and the leg affixed to the floor. Incrementally add load to the middle of the table until something gives. What will happen? A-the tabletop will give, spilling to books toward the far corner; B-The leg will bend and possibly break, tipping the top toward the far corner; or (the least likely) C-the leg will begin fracture/crumble at its weakest point (become detached from the ground) and the top will fall directly downward until the uncrumbled upper meets the uncrumbled lower and the resistance of that meeting tips the top in the direction of the far corner.

Riverwind · May 4, 2007

Incrementally add load to the middle of the table until something gives. What will happen?

Fine. Each time you increase the load the normal force on the remaining leg would increase to match the weight of the load. The system will remain motionless until something breaks.

The important thing to note is the leg must always support the full weight of the load - the system does not behave differently because the starting load happens to exceed the capacity of the leg. It makes no sense to claim that it would behave differently.

If you suddenly overload a leg then the leg will most likely collapse. Bending is the least likely outcome.

bush_cheney2004 · May 4, 2007

The important thing to note is the leg must always support the full weight of the load - the system does not behave differently because the starting load happens to exceed the capacity of the leg. It makes no sense to claim that it would behave differently.
If you suddenly overload a leg then the leg will most likely collapse. Bending is the least likely outcome.

Not necessarily.....statics analysis demonstrates that under compression, the leg member may collapse or buckle (bend), depending on the member's length, and assuming no zero force lateral support.

PolyNewbie · May 4, 2007

Riverwind:The important thing to note is the leg must always support the full weight of the load - the system does not behave differently because the starting load happens to exceed the capacity of the leg. It makes no sense to claim that it would behave differently.

No. The important thing to remember is that this is the internet and its full of annonymous posters who will try to sound like they know what they are talking about when in reality they have no idea. They are just out to waste everones time and make people think they know something. Its an ego sickness. Get help.

Figleaf, BC and myself have all told you the exact same thing but using different language. At least two out of the three have taken engineering statics. Take your physics elsewhere.

Riverwind · May 4, 2007

Not necessarily.....statics analysis demonstrates that under compression, the leg member may collapse or buckle (bend), depending on the member's length, and assuming no zero force lateral support.

That is my entire point - You can't say for certain what will happen but you can say that:

1) The leg will be supporting the entire load

2) The system will not start falling until something breaks.

3) The leg can collapse, snap or otherwise fail suddenly in a way that triggers a straightdown collapse.

Riverwind · May 4, 2007

If the leg doesn't fail and the table stays up then the load of the table is brought down on that one leg, but it is not a simple normal force as you describe.

Modelling the problem with a normal force is still valid no matter what happens at a microscopic level. You are the one who is claiming that the normal force could be less that the weight of the table - that is total nonsense.

We have a system where a leg with a support capacity of 4000N is suddenly trying to support 10000N - that would cause an immediate failure of the leg - there would be no time to bend or rotate and the system would have to fall straight down. Trying putting a book on a piece of spaghetti standing on its end - do you really think the spaghetti would be able to cause the book to tip before it shatters into pieces?

You can say that the leg might bend slightly before snapping but you cannot claim that the table will would always tip before it hits the ground. That is the point I trying to make -- a structure can collapse straight down after asymmetric damage.

None of your physics makes sense - its all wrong, but you had me confused with this whole table leg attached to the floor thing.

I did not confuse you - I clearly stated my assumptions. This is just another example of how you make things up when it suits you.

PolyNewbie · May 4, 2007

Riverwind: Modelling the problem with a normal force is still valid no matter what happens at a microscopic level.

No it isn't. A normal force is not the same thing as a moment. Apples are not the same thing as oranges. You cannot model apples with oranges.

Riverwind: You are the one who is claiming that the normal force could be less that the weight of the table - that is total nonsense.

No. I am claiming this normal force is silly and is another way of showing that you are completely wrong every time you make a scientific statement.

Riverwind: I did not confuse you - I clearly stated my assumptions. This is just another example of how you make things up when it suits you.

No. Every single thing you say about physics is always 100% wrong 100 % of the time that is why it is all confusing.

What kind of engineer are you ?

PolyNewbie · May 4, 2007

"Seven is exploding"
Welcome to all foreign readers. Luogocomune is a news commentary site (all in Italian, thus far) featuring a large, separate section on 9/11. In a way, the whole website revolves around the idea that unless that paramount, unacceptable lie called "the 9/11 terrorist attacks" is removed and put into right perspective, the downward spiral towards this new "dark age" of humanity will never stop.

Seven Is Exploding: Italian Mainstream TV

So there you go. Mainstream is now saying it.

All you really have to know is that GlobalResearch is saying it because when GlobalResearch or Alex Jones says something you can take it as 100 % credible.

See linked video on wtc7.

Riverwind · May 4, 2007

No it isn't. A normal force is not the same thing as a moment. Apples are not the same thing as oranges. You cannot model apples with oranges.

The table top is a body at rest - a static body analysis is a perfectly suitable analysis tool. You are only complaining because the analysis produces results that you don't like.

Do you really believe that a piece of spaghetti standing on its end could cause a book to rotate before it snapped? That is is what you are claiming.

PolyNewbie · May 4, 2007

Riverwind:The table top is a body at rest - a static body analysis is a perfectly suitable analysis tool. You are only complaining because the analysis produces results that you don't like.

A torque can be balanced by a counter torgue. No normal forces involved except those involved in creating the torgue. They are not coicident and cannot be added to form one normal force.

Please stop. Take a course in basic mechanics. You are polluting this thread with garbage and I am not here to teach basic statics.

buffycat · May 4, 2007

I'm having a hard time following the table example - it seems to me that it is only relevant if one has a one-legged table.

If there are four legs, then the mass of the table and the force of gravity acting upon it will distribute the weight evenly over all four legs (or three - if you like).

Now, unless ALL four legs fail in the same manner at the same time, there is a very good chance that the table top will not fall straight down (ie evenly over the 'footprint' of its four (or three) legs).

Have you not seen tables collapse? I have. And they don't all fall straight down.

I think this comparison is not workable.

kuzadd · May 4, 2007

Interestingly...

On April 16, 2007, a major Italian network (Canale 5) has aired some conclusive evidence that Building 7 did not collapse on its own, but was deliberately taken down with the use of explosives.

an excerpt from the series is archived here:

http://www.globalresearch.ca/index.php?con...&articleId=5550

scroll down. click and watch the exerpt.

what is most interesting, besides the video itself, is that in numerous other countries, 9/11 is discussed, televised, shows are made etc, on MSM, as opposed to alternative media in the US and Canada.

Dutch, British, Italian

For the rest of the series, go to luogocomune.net ( it is in italian)

For those who are interested, this is the entire, 42 min. presentation that was aired on Apr. 16th by Italian Canale 5, divided in the following 5 segments:

1 - Intro + Military stand-down.

2 - Pentagon + UA175

3 - WTC7 (the segment you just saw)

4 - Twin Towers + UA93

5 - 2 touching testimonies by W. Rodriguez and David "We were also killed on 9/11" Miller.

PolyNewbie · May 4, 2007

I like three legs. Ever notice that if you go into older restaurants with non flat floors and 4 legged tables that you will spill your coffee or beer because the table will rock at some point ?. If you have a three legged table it will never rock and this horrible calamity will never occur.

Restaurant owners please take note.

kuzadd · May 4, 2007

I'm having a hard time following the table example - it seems to me that it is only relevant if one has a one-legged table.
If there are four legs, then the mass of the table and the force of gravity acting upon it will distribute the weight evenly over all four legs (or three - if you like).

Now, unless ALL four legs fail in the same manner at the same time, there is a very good chance that the table top will not fall straight down (ie evenly over the 'footprint' of its four (or three) legs).

Have you not seen tables collapse? I have. And they don't all fall straight down.

I think this comparison is not workable.

I thought the same thing!

kuzadd · May 4, 2007

oh stignasty.........

latest news re: the freeway collapse.............it's going to reopen, sooner then thought, likely some of it within ten days, guess why?

it's structurally sound!!!!!!

YUP!

http://www.iht.com/articles/ap/2007/05/03/...ay-Collapse.php

http://www.guardian.co.uk/worldlatest/stor...6604264,00.html

http://www.msnbc.msn.com/id/18447152/

"A highway ramp shut down by the collapse of an overpass near the San Francisco-Oakland Bay Bridge won't have to be rebuilt from scratch and could reopen within 10 days, the governor said Wednesday."

because why???????

"Investigators found that the steel girders holding up the lower ramp had warped but remained structurally sound and could be straightened, California Department of Transportation spokesman Bob Haus said."

but remained structurally sound and could be straightened,

could you imagine, not only did that upper level, fall on that lower level, which then held fast and the steel remains structurally sound.

and is going to be reused!

Like I said this collapse dams the official story.

failure to pancake, failure to pulverize the concrete.

buildings completely pancaked and concrete completely pulverized, only on Sept 11th!

cybercoma · May 4, 2007

How is an overpass anything at all like the world trade center towers? And how are fires confined within a space, started by burning jet fuel and fueled by fabric, paper, wood and all sorts of other materials commonly found in offices at all even remotely comparable to this?

Having said that, although the steel supports remained structurally sound, they still warped. Whose to say that that kind of flex in the world trade centers wouldn't have caused them to come crashing down?

Regardless, we're talking apples and oranges.

stignasty · May 4, 2007

Having said that, although the steel supports remained structurally sound, they still warped. Whose to say that that kind of flex in the world trade centers wouldn't have caused them to come crashing down?

That was my point. One of the arguments that keeps being thrown out is that the fires weren't hot enough to melt the steel. This shows that it is possible for fire to weaken a structure to the point of collapse.

kuzadd · May 4, 2007

How is an overpass anything at all like the world trade center towers? And how are fires confined within a space, started by burning jet fuel and fueled by fabric, paper, wood and all sorts of other materials commonly found in offices at all even remotely comparable to this?
Having said that, although the steel supports remained structurally sound, they still warped. Whose to say that that kind of flex in the world trade centers wouldn't have caused them to come crashing down?

Regardless, we're talking apples and oranges.

I totally agree, I was originally not the one making the comparison, that was stignasty, for clarification.

Figleaf · May 4, 2007

Incrementally add load to the middle of the table until something gives. What will happen?
Fine. Each time you increase the load the normal force on the remaining leg would increase to match the weight of the load. The system will remain motionless until something breaks.
The important thing to note is the leg must always support the full weight of the load ...

Until something breaks.

- the system does not behave differently because the starting load happens to exceed the capacity of the leg. It makes no sense to claim that it would behave differently.
If you suddenly overload a leg then the leg will most likely collapse. Bending is the least likely outcome.

It seems like you chose to ignore the important part of my post: "What will happen? A-the tabletop will give, spilling to books toward the far corner; B-The leg will bend and possibly break, tipping the top toward the far corner; or (the least likely) C-the leg will begin fracture/crumble at its weakest point (become detached from the ground) and the top will fall directly downward until the uncrumbled upper meets the uncrumbled lower and the resistance of that meeting tips the top in the direction of the far corner."

With the leg at one corner, assuming the tabletop is perfectly rigid (which is a quite an assumption), if you increase the load on top uniformly across the whole surface (or in the center of the tabletop) the downward stress on the inside of the leg will be higher than the downward stress on the outside of the leg creating the possibility it will bend an possibly break from over-flexion on the outer side of the leg.

If it doesn't bend, it will crack/fracture/crumble at the weakest point in a direct downward direction UNTIL resistance from the intact upper portions of the leg (striking either the lower intact portion of the leg or the floor below). At that point, with the leg no longer being affixed to the floor, the table will topple in the direction of least resistance ... trhough the air in the direction of the corner furthest from the leg.

Consider:

T=top

C=center of gravity of the load (top)

L=upper leg

l=lower leg

W=weakes point of the leg

F=fracture/crumble

Image 1: Starting out

TTTTCTTTT

L

W

l

Image 2:

TTTTTTTTT <---Load added

TTTTCTTTT

L

F <---weight above compromises the leg here

l

Image 3:

TTTTTTTTT

TTTTCTTTT

L

. <---leg ceases to support load, and your assumption is the load moves straight down

l

Image 4:

TTTTTTTTT

TTTTCTTTT

L

L <--- upper portion falls straight down, impacts lower portion (i.e. meets resistance of lwr leg)

l

Image 5:

TTTTTTTTT

TTTTCTTTT ----> path of least resistance for table top

L

l <---- leg no longer fixed

l

Figleaf · May 4, 2007

I'm having a hard time following the table example - it seems to me that it is only relevant if one has a one-legged table.
If there are four legs, then the mass of the table and the force of gravity acting upon it will distribute the weight evenly over all four legs (or three - if you like).

Now, unless ALL four legs fail in the same manner at the same time, there is a very good chance that the table top will not fall straight down (ie evenly over the 'footprint' of its four (or three) legs).

Have you not seen tables collapse? I have. And they don't all fall straight down.

I think this comparison is not workable.

It's Riverwind's example, and it's a massive simplification, but it does work to some extent. What it shows, however, is that Riverwind is wrong.

You are right. Tables don't fall straight down unless the strenght of each and all the legs is overcome all together in perfect balance.

kuzadd · May 4, 2007

Having said that, although the steel supports remained structurally sound, they still warped. Whose to say that that kind of flex in the world trade centers wouldn't have caused them to come crashing down?

That was my point. One of the arguments that keeps being thrown out is that the fires weren't hot enough to melt the steel. This shows that it is possible for fire to weaken a structure to the point of collapse.

cybercoma: "Whose to say that that kind of flex in the world trade centers wouldn't have caused them to come crashing down?

Your assuming, the slight warping/twisting was from heat, it may or may not have been. It could have happened from the breaking away, of the structures from one another.

Well as of now NIST and FEMA, don't say that. IMO it's not credible or likely.

stignasty:

But, I don't know that anyone , ever argued/s that fire will not melt steel, eventually, under just right conditions, as that is a senseless arguement.

Example: welders with SPECIAL fuel mixes, melt steel to fuse, but note that is with specifc conditions.

The bridge collapse as of yet hasn't demonstrated that, either. It still could have been faulty construction, shoddy bolts, welds etc., I don't see that anything concrete has been demonstrated yet.

What it does clearly demonstrate is fire does not necessarily lead to catastrophic failure, nor pancake collapse, nor pulverized concrete That is quite clear.

ALSO: if they are stating the steel is structurally sound, then heat was a non-issue, because, the heat did not alter the steel. Example: when steel is heated, the steel itself is altered. it's mechanical properties would have changed. More specifically it would have changed the tensile strength of the steel. Therefore, if the steel had been heated to cause any weakening, it would NOT have been declared useable, as it would have been altered in such a way that it could not be structurally sound.