9/11 silly question

[valis]

Okay I will admit this is probably a really simple obvious question but I will ask anyway.

While listening to Coast to Coast am a week or two ago I heard some guy from the 9/11 scholars for truth. He repeatedly said that the towers could not have been brought down by an aircraft because the melting point of steel is X and the tempature jet fuel burns at is Y: X > Y, therefore the burning fuel could not have brought down the building.

This seemed to be a big thing with the guest as he yelled it repetadly to callers, saying the 'laws of physics' proved his point.

Okay here is the dumb question part, keep in mind I haven't taken physics yet...

Oh yeah...Put aside the issue of whether the steel even had to melt for the building to collapse, lets assume it did.

If the fuel is burning at X temp and is in an enclosed space; for instance the ceiling and floor and what are left of the walls are enclosing the fire somewhat, couldn't the temp in the building be higher than the burning temp of the jet fuel?

For instance if I have a light bulb whose surface reaches 100 degrees when operating and I put it in a box what will the tempeture in box reach; more than 100 degrees? If the heat has no where to go will it increase beyond a hundered degrees? So is the burning temp. of the fuel really a limit to the temps that could be reached in the fire?

edited to make question clearer

 

[ChaoticLimbs]

A simple flaw in these attempts to somehow turn a national tragedy into a conspiracy is that you don't need to melt steel to weaken it. All you need to do is heat it up. Burning jet fuel is more than sufficient to do that. Add an enclosed space and the mechanical damage of the plane severing supports and the weight bearing skin of the towers and it becomes very likely that the building would fall under its own weight.
The steel columns supporting the building were insulated (lower floors with Asbestos, upper floors with a non-asbestos substitute). There was a good reason to do this. Explosives are completely unnecessary to cause a collapse.
I've also heard people claim that the buildings fell in too controlled a manner, and that buildings shouldn't fall straight down. This also is rather silly when you consider that if an individual floor fails to support the upper floors, they'll fall straight down and the resulting energy release from the upper floors striking the next floor down is huge and primarily downward.
I'm not a physicist but I've not seen a credible trained physicist who actually believes that fuel can't take down a building like the WTC.

 

[valis]

A simple flaw in these attempts to somehow turn a national tragedy into a conspiracy is that you don't need to melt steel to weaken it...

I appriceate your answer and agree with it. The people doing this are fools and the gentleman I used the word scholar a little too often for my taste. I think he was a scholar like I am a porn star.

That said this isn't really what I am asking. What I am asking is if the heat source is contained somehow can the tempeture inside a container be higher than the tempeture of the heat source? Will the heat 'build up' or will it reach a maximum tempeture at that of the heat source?

 

[MetalPig]

If the fuel is burning at X temp and is in an enclosed space; for instance the ceiling and floor and what are left of the walls are enclosing the fire somewhat, couldn't the temp in the building be higher than the burning temp of the jet fuel?

No. You can't make stuff hotter than the heat source.

According to the conspiracy-debunkers, the jet fuel was spent within a very short time. After that, it was the building and the stuff in it that was burning. And apparently, that burned at a temperature high enough to weaken the steel in the central columns of the towers.

 

[Azrael 5]

All buildings collapse in on themselves-certainly at every demolition Ive seen(ok so they are controlled)dont they?

 

[Ririon]

All buildings collapse in on themselves-certainly at every demolition Ive seen(ok so they are controlled)dont they?

Newton says so. If a skyscraper was weakened at the base AND there was a very strong wind, then it might fall to one side while collapsing.

 

[Dcdrac]

They got hit by an aircraft full of jet fuel travelling at very high speed that is going to do it if nothing else.

 

[Ririon]

They got hit by an aircraft full of jet fuel travelling at very high speed that is going to do it if nothing else.

Assuming this was a reply to my post: Nope! The towers were still standing for minutes after being hit. So when they started collapsing, gravity did the work. And gravity prefers to work downwards.

 

[kookbreaker]

I would like to point out now that the 9/11 scholars for truth does not have a Structural Engineer, a Civil Engineer, a Demolition Expert, or any other relevant expert for that matter. The best they have is a fairly incompetant Physics Professor who has spent most of his life researching Cold Fusion. The remaining scholars are software engineers, reiligious studies professors, etc.

Is there a fallacy for appealing to ones own irrelevant authority?

 

[LTC8K6]

You only need about 800-1,000F to weaken the steel appreciably. The jet fuel was quite enough, anything else such as carpets and furniture just sped things along.

 

[LTC8K6]

If steel could withstand jet fuel burn temps, turbine blades would be a lot cheaper.

 

[gruk]

If steel could withstand jet fuel burn temps, turbine blades would be a lot cheaper.

To be fair, there's bound to be differences in the airflow inside a turbine and in a building with punctured outer walls. More air tends to generate a hotter flame (more oxygen per time unit, if nothing else).

Still, steel gets more malleable (and, I guess, less structurally sound) at a few hundred degrees celcius and I can quite imagine that an "office products and jet fuel" mix can burn that hot.

 

[rwguinn]

You only need about 800-1,000F to weaken the steel appreciably. The jet fuel was quite enough, anything else such as carpets and furniture just sped things along.

This is true.
At 600 degrees F, steel (generally) retains 95% of its room temperature ultimate strength. At 800 degrees, its at 88%, 1000 degrees, 58%, and at 1200 degrees, you're down to 37% of Ultimate (breaking) strength after 1/2 hour exposure.
Yield strengths are even lower--and once you start bending (or buckling, which in this case is the more likely scenario), things progress rapidly, since the geometry of the collumns is a large portion of their strength. Distort the geometry, and destroy the strength.

 

[LTC8K6]

gruk, I meant to put a at the end of that line.

 

[Buckaroo]

No. You can't make stuff hotter than the heat source.

It's not quite as simple as that. To use Valis's example, let's assume that you have a light bulb. When in radiative equilibrium with the open environment, the bulb has a surface temperature measuring 100 degrees C. Now place the the bulb in a box with reflecting sides that isolates it from the environment (but allows current to flow to the bulb). Now, the photons pouring from the bulb cannot escape the cavity, causing the temperature within to rise well above 100 C. The temperature will continue to rise until the bulb is switched off (blackbody physics come into play here, but I'm not going to get into that). In the real world, the box would isolate the bulb imperfectly, and the box itself would begin to radiate heat, so that the system would attain radiative equilibrium. The temperature in the cavity would still be much hotter than it would be otherwise. It all has to do with the distribution of the total heat flux, and the strength of the sink. Similar analyses can apply e.g. to the atmosphere, which is why the surface of the Earth is warm enough to live on, and indeed to the 9/11 case, where burning fuel (including the materials of the building itself) causes a more-or-less-constant flux of heat that is not necessarily able to escape the area efficiently.

This is not to take anything away from those who stated that steel can soften at relatively low temperatures -- which is undoubtedly true -- but it bolsters the case against the conspiracy types.

 

[rwguinn]

It's not quite as simple as that. To use Valis's example, let's assume that you have a light bulb. When in radiative equilibrium with the open environment, the bulb has a surface temperature measuring 100 degrees C. Now place the the bulb in a box with reflecting sides that isolates it from the environment (but allows current to flow to the bulb). Now, the photons pouring from the bulb cannot escape the cavity, causing the temperature within to rise well above 100 C. The temperature will continue to rise until the bulb is switched off (blackbody physics come into play here, but I'm not going to get into that). In the real world, the box would isolate the bulb imperfectly, and the box itself would begin to radiate heat, so that the system would attain radiative equilibrium. The temperature in the cavity would still be much hotter than it would be otherwise. It all has to do with the distribution of the total heat flux, and the strength of the sink. Similar analyses can apply e.g. to the atmosphere, which is why the surface of the Earth is warm enough to live on, and indeed to the 9/11 case, where burning fuel (including the materials of the building itself) causes a more-or-less-constant flux of heat that is not necessarily able to escape the area efficiently.

This is not to take anything away from those who stated that steel can soften at relatively low temperatures -- which is undoubtedly true -- but it bolsters the case against the conspiracy types.

Yes, it is as simple as that.
The temperature inside the box, or the surface of the box, will NOT be higher than the temperature of the source, which is the fillament of the bulb.
Period. Never. Ever. Not for any given value of time and space.
The bulb may not shed the heat as effectively as when in the open, which means the fillament gets hotter (which is why enclosed bulbs burn out faster than bare bulbs), but the maximum temperature attainable is that of the bulb. And that is limited by available current and voltage.
TANSTAAFL!

 

[Buckaroo]

Yes, it is as simple as that.
The temperature inside the box, or the surface of the box, will NOT be higher than the temperature of the source, which is the fillament of the bulb.
Period. Never. Ever. Not for any given value of time and space.
The bulb may not shed the heat as effectively as when in the open, which means the fillament gets hotter (which is why enclosed bulbs burn out faster than bare bulbs), but the maximum temperature attainable is that of the bulb. And that is limited by available current and voltage.
TANSTAAFL!

Nobody's talking about any free lunches here!

Maybe I was a little sloppy in making my point. As energy accumulates inside the box, the bulb/filament of course heats as well, so you are certainly correct that the temperature in the cavity immediately adjacent to the source will be the same as the source, and I did not mean to imply otherwise. But by your own statement, the temperature of an enclosed bulb does indeed increase over one that is in the open. Looking again at Valis's original question:

For instance if I have a light bulb whose surface reaches 100 degrees when operating and I put it in a box what will the tempeture in box reach; more than 100 degrees? If the heat has no where to go will it increase beyond a hundered degrees?

I think you'll agree that the answer to this question is yes.

I must disagree with you, though, about the temperature of the surface of an imperfectly reflecting box. Let's say we've left the system alone long enough to reach radiative equilibrium. Now, those filaments get darn hot. I sure as shootin' wouldn't want to put my finger on one. Yet I wouldn't hesitate to touch the box, which is waaayyy cooler. Why? The flux per unit area is waaaayyyy lower at the surface of the box. No worries about TANSTAAFL. Integrate around the box, and the flux balances perfectly with that from the filament. It's the distribution of energy, not the total amount of it, that's important in the context of the original question.

 

[rwguinn]

Nobody's talking about any free lunches here!

Maybe I was a little sloppy in making my point. As energy accumulates inside the box, the bulb/filament of course heats as well, so you are certainly correct that the temperature in the cavity immediately adjacent to the source will be the same as the source, and I did not mean to imply otherwise. But by your own statement, the temperature of an enclosed bulb does indeed increase over one that is in the open. Looking again at Valis's original question:



I think you'll agree that the answer to this question is yes.

I must disagree with you, though, about the temperature of the surface of an imperfectly reflecting box. Let's say we've left the system alone long enough to reach radiative equilibrium. Now, those filaments get darn hot. I sure as shootin' wouldn't want to put my finger on one. Yet I wouldn't hesitate to touch the box, which is waaayyy cooler. Why? The flux per unit area is waaaayyyy lower at the surface of the box. No worries about TANSTAAFL. Integrate around the box, and the flux balances perfectly with that from the filament. It's the distribution of energy, not the total amount of it, that's important in the context of the original question.

yes.

 

[Rob Lister]

If I remember correctly, the steel beams were only weakened slightly from the heat; just enough to allow them to sag a bit. This sagging caused the bolts that held the beams to shear. Had the bolts holding the beams been stronger, neither building would have collasped. They might have been total losses, but they'd have stood until intentionally brought down.

 

[rwguinn]

If I remember correctly, the steel beams were only weakened slightly from the heat; just enough to allow them to sag a bit. This sagging caused the bolts that held the beams to shear. Had the bolts holding the beams been stronger, neither building would have collasped. They might have been total losses, but they'd have stood until intentionally brought down.

You have a reference for that?
I'd be interested in reading it. My knowledge of buildings isn't that great--I usualy deal with stuff that moves--but I believe that they use rivets to hold these things together, and they are generally have as high, if not higher, shear strength than the beams they tie together.
Generally, we run a SF that is 2X or so that of the structural members themselves