Ask any question you want about Physics

originally posted by: Mary Rose
Is there a phenomenon called low temperature thermal expansion in physics, or not?

I'm not going to get into any 9/11 specifics and for reasons I can only guess, the person posting 9/11 specifics in this thread was apparently banned.

But as long as it's a general physics question, like this, it's on topic here.

However you didn't get the point of my previous post, perhaps because I didn't make this clear enough:

Most computers use binary 1s and 0s. Most science is not binary like this, and if you ask true/false questions in a binary fashion you will never understand science. Going back to the parallax topic, here's a question:

True or false? We can measure the parallax of stars.

It's true.
It's also false.

You have to stop thinking in a binary fashion to understand science. It's true in some cases and false in other cases, depending on the distance.

The phrase "low temperature thermal expansion" without context is meaningless. Avoiding any 9/11 specifics, I will say this:

Government guidelines talk about the possible structural failure of buildings if their design doesn't allow for thermal expansion, which needs to range from the coldest day of winter to the hottest day of summer, plus some safety margin in case we set new records. If the building is designed for, say, thermal expansion from -25°C to +50°C, this is a 75 degree temperature range and thermal expansion in such an anticipated design range should not cause structural failure.

So what happens if there's an office fire that can get hotter than the hottest day in summer (say, 800°C versus 50°C), do you think that extra 750°C worth of thermal expansion could cause problems for the structural integrity of the building, when it's 10 times larger than the 75°C range the building was designed for?

If any tall building has a large fire, get out as fast as you can because it may only remain standing long enough to evacuate the building. If the building isn't rectangular in shape, get out even faster.

"Low" to a physicist can have many meanings,but without any qualification an astrophysicist would probably define low temperature as a few degrees above absolute zero. Buildings on Earth aren't designed for such temperatures. To avoid ambiguity one should specify the temperature range of interest when talking about thermal expansion since "low" isn't sufficiently descriptive to be meaningful without some context, (many claims posted by the deleted account were taken out of context).

originally posted by: hgfbob

so YOU tell me all about this NEW physics of LOW TEMP thermal expansion and HOW it removed the necessary structural RESISTANCE to allow global unified ACCELERATION equal to g. to occur for 105 vertical feet for 1/3 of the 6.5 second collapse.

9/11 crap again?

OK, physics. In a building, there's more load on the bottom structural members than the top, because there's heavy stuff above them. Get a dynamic load (something above bashed), it travels at the speed of sound in the material and overloads and breaks the supports. Ones on the bottom are closer to their limits already because the building is heavy. Under anomalous stress, they break first. If there's nothing holding up the top stuff, it falls at 'g', like everything else on the surface of the planet. There's nothing surprising whatsoever about a million tons of concrete & steel falling at 'g'.

Real buildings being destroyed fall down, because gravity is down, not like Hollywood models being "blown up" from the inside with pyrotechnics. Controlled and uncontrolled demolition looks the same because gravity is the same, but the latter case it's more messy and more collateral damage, as there was in NYC.

a reply to: dragonridr

First things first and one thing at a time.

I asked whether or not the following is true or false:

originally posted by: hgfbob
Simple fact of SCIENCE: if any of the potential energy from the accelerating mass went to destroying itself, it will lose kinetic energy which requires that the building slow in its fall.......but since it did fall at free-fall acceleration, it wasn't causing itself to collapse.

The above is talking about “potential energy,” “accelerating mass,” “kinetic energy,” "slow in its fall," “free-fall acceleration,” and “causing itself to collapse.”

First, is “free-fall acceleration” the same as or different from “causing itself to collapse”?

a reply to: Mary Rose


Ok ill make this easy gravity from the earth always has the same pull on an object no matter its mass. Now for a building collapse to reach terminal velocity is impossible because there will be resistance at some point during the collapse. So terminal velocity of an object falling 90 meters per second.

So say we have an object say 400 meters tall at terminal velocity the building would collapse in 4.4 seconds. Problem is a building will always encounter some resistance extending the time it takes. Just like earlier when we discussed force the force countering gravity is the resistance any undamaged supports can provide. But eventually do to sheer mass this resistance eventually becomes negligible.

a reply to: dragonridr

Please answer my question.

Again, is “free-fall acceleration” the same as or different from “causing itself to collapse"?

Which one?

Isn't the free fall vel 11ft/sec?
a reply to: dragonridr

a reply to: Mary Rose

That's silly. When the stuff is being accelerated down at 'g' it isn't being destroyed. When that stuff happens to hit something solid and stops suddenly then yes it is destroyed.

Drop an egg. Looks great going down, but there's a problem when it stops falling.

originally posted by: Nochzwei
Isn't the free fall vel 11ft/sec?
a reply to: dragonridr

9.8 meters a second squared....meaning every second the rate of acceleration doubles till the terminal velocity is reached.

we can open any reputable physics text or website to see this...."rate of acceleration of all mass regardless of weight, towards the earth, at sea level, within a vacuum is 9.8m/s^2."

any mass occurring an interval of acceleration equal to gravity has all resistance below removed in order to allow that mass to accelerate........if there is something there, there is no acceleration.

a reply to: Nochzwei

Can you please answer my question:

Introduction:

originally posted by: hgfbob
Simple fact of SCIENCE: if any of the potential energy from the accelerating mass went to destroying itself, it will lose kinetic energy which requires that the building slow in its fall.......but since it did fall at free-fall acceleration, it wasn't causing itself to collapse.

The above is talking about “potential energy,” “accelerating mass,” “kinetic energy,” "slow in its fall," “free-fall acceleration,” and “causing itself to collapse.”

Question: . . . is “free-fall acceleration” the same as or different from “causing itself to collapse”?

a reply to: Mary Rose

sorry but you will not get a straight answer from them.


mass can not both accelerate at g. and make the path it falls into....not without the use of a huge external force applied....gravity is not that robust a source of force.

a natural gravitational collapse occurring from the load bearing members being compromised, uses the collapse of the unsupported mass above in order to collapse mass below.

structural mass accelerating equal to g. already has that resistance removed in order to constantly accelerate.

Correct in vac terminal vel is reached when the inertia of the falling object kicks in and is equal to the mass
a reply to: soundstyle

Physics Question: is a frog's butt water tight and if so can water molecules quantum tunnel past that barrier in any way?

a reply to: dragonridr

Problem is a building will always encounter some resistance extending the time it takes.

a building is comprised of many redundant overlapping applications bound together to form a single unit.

not only are you going to get constant resistance from below, you get it laterally and diagonally also.

it is physically impossible for a building to both accelerate and make the path it falls into using it's own force......and since the above posts asked how a hypothesized claim of low temp thermal expansion occurring makes this possible within a steel frame.....I would really like to know.

originally posted by: stormbringer1701
Physics Question: is a frog's butt water tight and if so can water molecules quantum tunnel past that barrier in any way?

Lol. If they did, it will drown

originally posted by: soundstyle
a reply to: dragonridr

Problem is a building will always encounter some resistance extending the time it takes.

a building is comprised of many redundant overlapping applications bound together to form a single unit.

not only are you going to get constant resistance from below, you get it laterally and diagonally also.

it is physically impossible for a building to both accelerate and make the path it falls into using it's own force......and since the above posts asked how a hypothesized claim of low temp thermal expansion occurring makes this possible within a steel frame.....I would really like to know.

Your another person who needs to find out about DYNAMIC LOADING and the floor system of the towers!

originally posted by: soundstyle
a reply to: Mary Rose

sorry but you will not get a straight answer from them.


mass can not both accelerate at g. and make the path it falls into....not without the use of a huge external force applied....gravity is not that robust a source of force.

Well you wont have to worry then if you are in an AVALANCHE

originally posted by: soundstyle
a reply to: Mary Rose

sorry but you will not get a straight answer from them.

Thank you, but first, why not?

originally posted by: soundstyle

mass can not both accelerate at g. and make the path it falls into....not without the use of a huge external force applied....gravity is not that robust a source of force.

a natural gravitational collapse occurring from the load bearing members being compromised, uses the collapse of the unsupported mass above in order to collapse mass below.

structural mass accelerating equal to g. already has that resistance removed in order to constantly accelerate.

Are you stating the same thing, in different words, as the quote in question:

originally posted by: hgfbob
Simple fact of SCIENCE: if any of the potential energy from the accelerating mass went to destroying itself, it will lose kinetic energy which requires that the building slow in its fall.......but since it did fall at free-fall acceleration, it wasn't causing itself to collapse.

And is the quote by hgfbob accurately paraphrasing the scientific position put forth in the government report in question?

a reply to: wmd_2008

Well you wont have to worry then if you are in an AVALANCHE

and how does this apply to a buildings structural mass accelerating equal to gravity?

Your another person who needs to find out about DYNAMIC LOADING and the floor system of the towers!

load was redistributed and the floors are non load bearing to the building....they are attached to the columns, sitting on plates.

all I see on the HGF posts are support for what is posted, links to what is said and whom said it to show they are not the words of the person posting, along with a 'crash-course' in basics, .....you really should try that sometimes if you are expected to be taken seriously.

a reply to: Mary Rose

Thank you, but first, why not?

they can't without showing the official claims the utter failure they are.

and yes, the same thing

And is the quote by hgfbob accurately paraphrasing the scientific position put forth in the government report in question?

oh no....it's telling what must occur for 105 vertical feet in WTC7 in order to accelerate equal to g..

the scientific position put fourth claims a new physics phenomenon of low temp thermal expansion makes this physics impossibility, a possibility......well that is if they could prove it.

that is the intent of the original post by HGF...to have someone explain this phenomenon no one knows about.

originally posted by: soundstyle
a reply to: wmd_2008

Well you wont have to worry then if you are in an AVALANCHE

and how does this apply to a buildings structural mass accelerating equal to gravity?

Your another person who needs to find out about DYNAMIC LOADING and the floor system of the towers!

load was redistributed and the floors are non load bearing to the building....they are attached to the columns, sitting on plates.

all I see on the HGF posts are support for what is posted, links to what is said and whom said it to show they are not the words of the person posting, along with a 'crash-course' in basics, .....you really should try that sometimes if you are expected to be taken seriously.

Sorry mate but I have 30+ years in construction first job in the design/drawing office for a STRUCTURAL STEELWORK company, also have done various other TECHNICAL jobs on site including testing various STRUCTURAL components sometimes to destruction, how do you think an avalanche is POWERED, by the snow fairies

The floors in the twin towers were suspended between the inner core wall and outer wall an MASS that fell on those VAST 42,000 sq ft slabs could only repeat ONLY be resisted by the connections of that individual slab irrespective of the amount of mass below. those connections were identical on all floors apart from the service floors.
They were designed to take their on mass, the people office equipment etc for the floors PLUS a safety margin.

Now if you really want to continue post on 9/11 threads!!!