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Author Topic: What is Free Fall?  (Read 62692 times)

Offline Aemilius

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Re: What is free fall?
« Reply #125 on: 06/01/2014 17:47:47 »
....I got bored of refuting absurd claims about the tower falling years ago.

If your entrance is any example, you couldn't refute a fairy tale.

 

Offline Aemilius

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Re: What is free fall?
« Reply #126 on: 09/01/2014 02:34:11 »
This was presented as an anonymous 47 story tall building so there wouldn't be any reason for any theory to fall into the category of "Not Allowed" or "Off Limits". All a theory has to do is be consistent with physical principles and display a solid behavioural correspondence (a predictable outcome similar to confirmed observations) in order not to be "ruled out" as a possible contender that explains the whole thing. It's not a whodunit, it's a howdidit. For the analysis it doesn't matter who the tenants may have been, why anyone might have done it, how they could have done it, whether anyone saw Bin Laden's face in the smoke or a lizard changing into George W. Bush, or even what the name of the building was or where it was located.... and it doesn't matter if "some shits" were flying around in planes full of jet fuel either.

My position hasn't changed....

It's physically impossible for the lower part of the building to have progressively/naturally collapsed (below) in any way that could result in the upper part of the building symmetrically descending straight down through itself, through the path of greatest resistance at anything near gravitational acceleration for any period of time, and there is absolutely no mode or combination of modes of progressive/natural structural failure driven solely by gravity....


....that can ever give rise to the conditions required (below) for free fall to have occurred at any point during its descent....


....and anyone who believes otherwise (below) belongs in a lunatic asylum.....


 
So, Bored chemist, if you want to haul yourself aboard the sinking ship of Dr. Calverds theory and believe all the evidence supports his point of view, at what point during his theoretical post catastrophic aerostatic blowout/speed of sound stress propagation/spontaneous progressive structural disintegration collapse would you say....
 
"Hold it.... Right there! That's the point where all the columns
will undoubtedly be found behaving in a manner very
much like air (left).... it will take very careful calculation
to tell the fall times apart during this period of
the ongoing progressive structural failure (right)."


Dr. Calverds position is that not only is it possible but probable that the lower part of the building progressively/naturally collapsed in a way that resulted in the upper part of the building actually accelerating as it descended symmetrically straight down through itself, through the path of greatest resistance (below right), and also, incredibly, that driven on solely by gravity it actually continued to accelerate so nearly to gravitational acceleration (below left) as to require very careful calculation for any difference between the two to be detected.


I don't really have a theory per se, but if I had to choose one, it would obviously have to be Dr. Calverds other model, the "explosion" model (below left) that was skipped over in favor of the "aerostatic" model (below right) because the explosion model, unlike the aerostatic model, can actually create the conditions required for free fall to occur (below center). The explosion model clearly shows an immediate and solid one to one behavioural correspondence with the confirmed observation of gravitational acceleration, and it can easily account for that at any point during the descent of the upper part of the building anytime one wishes.... in contrast to the fantastic catastrophic aerostatic blowout/speed of sound stress propagation/catastrophic spontaneous progressive disintegration invention that, oh yeah, leaves all the columns and support structure in place!


So far, the explosion model (below) is the only one....


....that can realistically match and be expected to create the conditions (below) that we know must have existed....


....beneath the literally falling visible upper part of the building (below) during its observed largely symmetrical descent at gravitational acceleration for approximately 105 feet in 2.25 seconds.


So the closest thing to a theory I have (and in answer to Dr. Calverds earlier question about what I think happenned), at least at this point, would go something like....

Judging by the confirmed observation of a significant period of gravitational acceleration, a high probabilty exists that an explosion or other type of event must have occurred that was powerful enough to quickly remove the support from beneath the upper part of the building (below right), either all at once or incrementally in advance of its descent, permitting it to descend at gravitational acceleration for the observed period and under the conditions required (below left) for free fall to occur.



« Last Edit: 03/05/2015 10:48:12 by Aemilius »
 

Offline Bored chemist

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Re: What is free fall?
« Reply #127 on: 12/01/2014 13:13:31 »
....I got bored of refuting absurd claims about the tower falling years ago.

Care to show what's wrong with my assertion about the number of video lines, and the best available precision on the fall rate?
 

Offline alancalverd

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Re: What is free fall?
« Reply #128 on: 13/01/2014 11:50:59 »
OK, back in the swim.

Let's have an explosion. But it clearly (according to the NIST velocity graph) occured about 2 seconds after the west penthouse started moving so it wasn't the primary cause of collapse, nor did it cause much debris to be ejected. A very interesting scenario indeed. How was it orchestrated, and what explosive produces more suck than blow?
 

Offline Aemilius

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Re: What is free fall?
« Reply #129 on: 13/01/2014 22:32:19 »
OK, back in the swim.

Thank God (figuratively speaking).
« Last Edit: 14/01/2014 10:21:00 by Aemilius »
 

Offline JP

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Re: What is free fall?
« Reply #130 on: 16/01/2014 23:26:29 »
Calling other people's claims "worthless crap" is pushing the rule to "keep it friendly" on the forum.  Please try to stay civil in here.

Thanks,
The Mods
 

Offline Aemilius

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Re: What is free fall?
« Reply #131 on: 21/01/2014 21:11:04 »
Hello JP (nice to meet you)....

I understand the "keep it friendly" rule JP, and I think the fact that the ongoing discussion between Dr. Calverd and I has been a perfectly civil and enjoyable exchange (even when mildly contentious) clearly demonstrates that. I'll not repeat what I said earlier, but neither will I take it back. When it comes to the insulting monument to irrelevance that is reply 113 though, let me ask you this....

How does one respond to an immediate and open display of hostility in a "friendly and civil" way? Between just which two blows of his broadsword did you expect me to reach out to this Bored chemist fellow?
« Last Edit: 28/04/2015 22:40:32 by Aemilius »
 

Offline Aemilius

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Re: What is free fall?
« Reply #132 on: 21/01/2014 21:14:35 »
Hi Dr.Calverd....
 
Especially interested (actually dying) to read your take on all this.... Can you make sense of anything this Bored chemist fellow has written?
 
By the way, I'm looking forward to exploring the explosion model with you, but since we're sort of in between the "aerostatic" and "explosion" models, I think I'll take a bit of a break for a week or so. Just wanted you to know I haven't lost interest.

Take care.
 

Offline Aemilius

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Re: What is free fall?
« Reply #133 on: 21/01/2014 21:16:12 »
Hey Bored chemist....

Look man, in spite of the Moderators admonition, I have to stand by my characterization of your reply 113....

I can't speak for anyone else, but I didn't bother to get involved in this discussion because I got bored of refuting absurd claims about the tower falling years ago.

All the evidence supports Alan's point of view.

It fell down because some shits flew a plane full of jet fuel into it.
That fire heated the steelwork until it failed. The upper floors fell down and, since skyscrapers are not designed to take massive vertical shock loads, the rest collapsed.
It's not possible to analyse the video footage accurately enough to measure the acceleration to a high enough precision to rule out near free fall.
Typical video pictures are about 500 hundred lines high, and the image falls through about half the frame height so, at best you can measure the height of the building in each frame to about 1 part in 250.
That's simply not enough precision to rule out the suggestion that the building fell down.

You have, essentially, no evidence; but you have wasted 5 pages talking about it.

Anyone joining in with the discussion to point this out to you wouldn't have stopped you rambling on about it.

I openly challenged you to back it up (using quotes/links/articles) or take it back and you've done neither. Instead, you now seem more interested in trying to take the helm and steer the focus of the thread to grilling me about why some aspect of your invisible plane full of jet fuel claim/assertion won't work, and now you're even trying to imply an appeal to authority on my part for citing NIST data, ostensibly in support of some imaginary claim you think I've made....  I've advanced no theory, nor have I made any claims or assertions of any kind.
 
Why are you demanding answers to questions from the anonymous eighth grade dropout questioner instead of just asking Dr. Calverd, a recognized bona fide veteran research Physicist eminently qualified to answer them? As anyone can see, you're just not making any sense!

I don't have any academic credibility and I didn't come here to give answers, I came here to get answers from the brighter lights here. I didn't set out to see you in a negative light either, but until you address/account for what you wrote in reply 113, I have no choice....

At this point you've proven nothing, you've backed up nothing, you've taken back nothing, you've refuted nothing, your invisble fuel laden plane theory (if that's what it is) makes no sense and your focus on me instead of the topic is just odd.... I honestly can't see where you've really said anything at all!

In view of all that and pending some sort of coherent explanation, I'm just going to ignore your posts.
« Last Edit: 22/01/2014 00:50:42 by Aemilius »
 

Offline JP

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Re: What is free fall?
« Reply #134 on: 21/01/2014 22:41:36 »
How does one respond to an immediate and open display of hostility in a "friendly" way? Between just which two blows of his broadsword did you expect me to reach out to this Bored chemist fellow?

You're supposed to keep the tone of the conversation friendly and civil.  If you (or other users) can't do this, the thread will be locked.  Your recent responses are in line with this rule of civility.
 

Offline MrVat7

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Re: What is free fall?
« Reply #135 on: 22/01/2014 08:15:27 »
Falling under action of only one force - gravity
 

Offline Bored chemist

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Re: What is free fall?
« Reply #136 on: 22/01/2014 19:20:25 »
Hey Bored chemist....

Look man, in spite of the Moderators admonition, I have to stand by my characterization of your reply 113....

I can't speak for anyone else, but I didn't bother to get involved in this discussion because I got bored of refuting absurd claims about the tower falling years ago.

All the evidence supports Alan's point of view.

It fell down because some shits flew a plane full of jet fuel into it.
That fire heated the steelwork until it failed. The upper floors fell down and, since skyscrapers are not designed to take massive vertical shock loads, the rest collapsed.
It's not possible to analyse the video footage accurately enough to measure the acceleration to a high enough precision to rule out near free fall.
Typical video pictures are about 500 hundred lines high, and the image falls through about half the frame height so, at best you can measure the height of the building in each frame to about 1 part in 250.
That's simply not enough precision to rule out the suggestion that the building fell down.

You have, essentially, no evidence; but you have wasted 5 pages talking about it.

Anyone joining in with the discussion to point this out to you wouldn't have stopped you rambling on about it.

I openly challenged you to back it up (using quotes/links/articles) or take it back and you've done neither. Instead, you now seem more interested in trying to take the helm and steer the focus of the thread to grilling me about why some aspect of your invisible plane full of jet fuel claim/assertion won't work, and now you're even trying to imply an appeal to authority on my part for citing NIST data, ostensibly in support of some imaginary claim you think I've made....  I've advanced no theory, nor have I made any claims or assertions of any kind.
 
Why are you demanding answers to questions from the anonymous eighth grade dropout questioner instead of just asking Dr. Calverd, a recognized bona fide veteran research Physicist eminently qualified to answer them? As anyone can see, you're just not making any sense!

I don't have any academic credibility and I didn't come here to give answers, I came here to get answers from the brighter lights here. I didn't set out to see you in a negative light either, but until you address/account for what you wrote in reply 113, I have no choice....

At this point you've proven nothing, you've backed up nothing, you've taken back nothing, you've refuted nothing, your invisble fuel laden plane theory (if that's what it is) makes no sense and your focus on me instead of the topic is just odd.... I honestly can't see where you've really said anything at all!

In view of all that and pending some sort of coherent explanation, I'm just going to ignore your posts.

Care to show what's wrong with my assertion about the number of video lines, and the best available precision on the fall rate?
 

Offline Aemilius

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Well Bored chemist, your last post makes just as much sense as your first.... none. At least you're consistent!

It's been about three weeks now since you crash landed in this thread with the monument to irrelevance that is reply 113. All you've done since then is to repeat the same question like an old broken record player. Do you think it makes you appear intelligent endlessly waving around the same question about the precise measurement of free fall Bored chemist? Do you think that maybe it distracts people from noticing that your posts lack even a nanogram of substance/relevance? How long will you continue with this buffoonery? Everyone can see there's no logical explanation for it.... What's the deal man?

As it turns out, you're the one who's actually doing all the things you've accused me of. It is you who has made an absurd and easily refuted claim. It is you who has no evidence, essential or otherwise, supporting your view. It is you who continues to "waste space". It is you who continues to ramble on, repeating the same question in response to my repeated requests that you back up what you wrote.

Care to show what's wrong with my assertion about the number of video lines, and the best available precision on the fall rate?

I already told you, I'm just an eighth grade dropout, so I can't honestly say I know what's wrong with your so called "assertion" about the number of video lines or what the best available precision is on the fall rate. I tried to ask Dr. Calverd for his opinion of it in reply 135. My guess is the reason he hasn't responded is that he sees your post as radioactive and doesn't want to get anywhere near it. Why don't you try asking him yourself? Why are you avoiding that option here?

You may think you're being clever with all this nonsense, but the only one you're fooling is yourself. Go ahead and keep responding though if you enjoy watching what's left of your now shredded credibility in this thread repeatedly being raked over the coals (in a friendly and civil way of course) by an eighth grade dropout!
« Last Edit: 27/01/2014 06:17:16 by Aemilius »
 

Offline alancalverd

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Care to show what's wrong with my assertion about the number of video lines, and the best available precision on the fall rate?

Behave, children!

If the reference point just crosses 200 lines, and there's no uncertainty in the timebase, you can estimate the fall distance to better than +/- 0.5% and the elapsed time to within a couple of microseconds by simple frame analysis. Modern videocamera timebases are very stable and consistent. The NIST graph seems pretty good to me.
 

Offline Aemilius

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Excellent Dr. Calverd, and just what I intuitively suspected (but might have had a bit of trouble elucidating).

Just to be clear though.... You're saying the assertion being made by Bored chemist that it's not possible to analyse the video accurately enough to prove free fall/near free fall is in error.

Is that correct?
« Last Edit: 04/05/2016 17:42:38 by Aemilius »
 

Offline alancalverd

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I think NIST can analyse a video reasonably well.
 

Offline Aemilius

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I'll take that as a "Yes".
« Last Edit: 28/01/2014 08:23:30 by Aemilius »
 

Offline Aemilius

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I think I'll skip any further discussion of this, it's actually starting to give me the creeps....

I have Dr. Alan Calverd Ph.D. (a well seasoned career research physicist) arguing that not only is it possible but probable that the lower part of the building progressively/naturally collapsed in a way that resulted in the upper part of the building actually accelerating as it descended symmetrically straight down through itself, through the path of greatest resistance (below left), and also, incredibly, that driven on solely by gravity it quite naturally continued to accelerate so nearly to gravitational acceleration (below right) as to require very careful calculation for any difference between the two fall times to be detected.... preposterous!


There appears to be a considerable number of views of the thread but, eerily, not one member is commenting on the veracity of what I've had to say, and neither is anyone commenting on the veracity of what Dr. Calverd has had to say either.... very strange indeed!
 
A clearly irrational and insulting post made by Bored chemist slips past the moderators, but I am openly admonished for not "keeping it friendly" when I bluntly challenge/recognize his absurd baseless assertion for what it is.... a now confirmed load of rubbish!

Finally, CliffordK has explained to me (privately) that he and the other moderators decided that arguments about whether or not two jet airplanes caused the building to collapse seemed best suited to the "That CAN'T be true" subforum, though no airplane struck the building (even the NIST says airplanes had nothing to do with it) and airplanes are mentioned nowhere in the thread as having had anything to do with it either.... extremely curious!

To top it all off, compared to the meticulously factual and clearly defined hard science question I posed concerning the obvious impossibility of even near free fall occurring during any natural progressive structural failure, there seems to be no problem with topics like how much to tax the price of a drink or baggy shirts causing some guy to sweat being considered as "General Science"..... incredible!

Not meant to offend, I just don't get any of that. Thread abandoned (for now).... Lock it, leave it, do as you wish.

« Last Edit: 19/07/2015 11:17:42 by Aemilius »
 

Offline Aemilius

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Re: What is free fall?
« Reply #143 on: 12/09/2014 07:43:17 »
Quote from: alancalverd
Let's have an explosion.

Right Dr. Calverd, we might as well, since, as we've both really
known all along, it's the only logical way to explain observations.

WTC7 - ANALYSIS AND CONCLUSION

A complete Prima Facie Empirically Verifiable Scientific
Method Driven Graphical Target System Analysis and
Conclusion arrived at by Process of Elimination




"Analogical models are a method of representing
a phenomenon of the world, often called the 'target system',
by another, more understandable or analysable system. They
are also called dynamical analogies." - Wikipedia


The exceptionless condition required for gravitational acceleration
to occur has been known for centuries....



....and is, as you pointed out initially "The condition under which
a body is, literally, free to fall under the influence of the local
gravitational field with no resistance to its acceleration.
"....



The Control, or source system, that appears to the right of the
Scenario, or target system, in many of the animations is
intended as a reminder of that, and also signals the
beginning of a comparison....



We can still know with certainty what condition exists beneath
an object as it falls....



....even though we may not be able to see into the space
beneath it as it does....



Buckled columns, whether one or a hundred, whether one at a
time or all at once (or any combination thereof) won't just go
from 100% to 0% when they buckle, they'll gradually
decrease in strength while they buckle
and that takes time....



The mechanism of buckling (a mode of natural progressive
structural failure), whether caused by heat....



....or by overloading....



....or by other modes of natural progressive structural failure
such as impact induced fracturing....



....or fracturing caused by overloading....



....or any other mode or combination of modes of natural
progressive structural failure absolutely cannot match or
create the exceptionless condition required for gravitational
acceleration to occur, it's literally impossible (naturally excluding
the consideration of bridges and other structures that pass through
air wherein the condition required for gravitational acceleration to
occur exists inherently as a structural feature). There is no such
thing as structural gravitational acceleration....



The progressive collapse of the building (NIST probable
collapse sequence starting with column 79 on the left)....



....that essentially happens all at once....



....is clearly physically inconsistent with what we
empirically know of natural progressive structural failure
(defined as a time consuming process of individual, sequential
or simultaneous failure involving one or a number of related
structural components). It's a physical impossibility for the
lower part of the asymmetrically damaged building
(reportedly three core columns and nine perimeter
columns) to have naturally progressively collapsed
in any way that could result in the upper part of
the building symmetrically descending as a single
unit straight down through itself.... 



....at anything near gravitational acceleration (NIST
probable collapse sequence starting with column 79 circled
below) for any period of time....



A building collapse like that seen below resulting from any
natural progressive structural failure of a steel frame building
including a 105 foot 2.25 second period of gravitational
acceleration of the upper part of the building as a single
unit is an absolute physical impossibility....



....as nowhere in the course of any such collapse or
structural failure is the exceptionless condition required
for gravitational acceleration to occur seen to arise beneath
the upper part of the building as the scenario
plays out to completion....



There is absolutely no mode or combination of modes
of natural progressive structural failure driven solely
by gravity that can ever match or give rise to the
exceptionless condition required for free fall to have
occurred at any point during it's descent....



The scenario playing out below is an absolute physical
impossibility. Just as there is no such thing as structural
gravitational acceleration
, nor is there any structural failure
mode known as natural progressive structural
gravitational acceleration
....



There is simply no point during a natural progressive gravity
driven collapse of any modern steel frame skyscraper
where one could realistically say....

"Hold it.... right there! That's the point past which all
the welded and bolted together steel columns and
structural components
that were supporting the building
just a moment ago (with an area greater than that of
a football field) will undoubtedly be observed beginning
and then continuing to behave in a manner indistinguishable
from  air
(below left) for at least the next eight stories,
or 105 feet
of its descent (below right). It would take very
careful calculation
to tell apart the fall times shown below
during this free fall period of the ongoing natural
progressive structural failure
"....




For the 105 foot 2.25 second period of time that we know
the upper part of the building literally fell as a single unit at
gravitational acceleration we know it can not have been
using any of it's potential energy to crush the building
contents, columns and other structural components
beneath it and undergo gravitational acceleration
at the same time (as illustrated by this
frangible impedance scenario)....



It's physically impossible for the lower asymmetrically
damaged part of the building to have naturally progressively
collapsed in any way that could result in the upper part of
the building actually accelerating as it descended symmetrically straight
down through itself as a single unit through the path of maximum
resistance (below right), and then, driven on solely
by gravity, actually continue to accelerate so nearly to
gravitational acceleration (below left) as to require very
careful calculation
for any difference between
the two to be detected....



Some other force powerful enough to quickly remove all
support
from beneath the upper part of the building as it
descended must be introduced to explain the observed
rate of descent during the 2.25 second period of gravitational
acceleration. For the 2.25 seconds that the building literally fell
at gravitational acceleration, no other force powerful enough to
quickly remove all support from beneath the upper part of the
building was seen to be introduced from outside the building,
and no other force powerful enough to quickly remove all
support
from beneath the upper part of the building is known
to have existed inside the building as an element or normal
function of it's infrastructure. For a load supported by a column
to descend at gravitational acceleration, all support must be
quickly removed, there's absolutely no other way. It must be
knocked out, pulled out, blown out, vaporized etc.
Since no eight story tall boulders were seen rumbling
through Manhatten that day that could have
quickly knocked out all support....



....and no suspicious looking Frenchmen were spotted rigging
for verinage (another form of controlled demolition) the night
before that could have quickly pulled out all support....



....and no bombs or rockets were seen to be dropped on/fired
at it that could have quickly blown out all support....



....and no giant laser beams or other secret weapons were
being tested in the area that could have quickly
vaporized all support....



....and no other force capable of quickly removing all
support from beneath the upper part of the building existed
in the building as a normal function of it's infrastructure (blue)....



....it naturally follows that whatever the other force was
that must be introduced to explain the observed 105 foot 2.25
second period of gravitional acceleration of the upper part of the
building as a single unit, it must have been introduced some time
before the event, and unless it can be shown how the other
force
that must be introduced either during or just before
the collapse of the building was introduced from outside
the building, or that it was already existing inside the
building as a normal function of it's infrastructure, the
process of elimination really leaves only one possible
explanation for the building's behaviour. Some energetic
material powerful enough to quickly remove all support
from beneath the upper part of the building during the 105
foot 2.25 second period of gravitational acceleration must
have been physically transported inside the building some
time before the event, it had to be brought in. The
explosion model is the only one....



....that can realistically match and empirically be
expected to create the exceptionless condition that
we know must have existed....



....beneath the literally falling visible upper part of
the building as a single unit during its observed largely
symmetrical descent at gravitational acceleration for
approximately 105 feet in 2.25 seconds....



The undisputed (both the NIST and independent researchers
alike agree) observation of a significant well defined period of
gravitational acceleration of the upper part of the
building as a single unit....



Stage 1 (0 to 1.75 seconds): acceleration less than
that of gravity (i.e., slower than free fall).

Stage 2 (1.75 to 4.0 seconds): gravitational
acceleration (free fall).
During Stage 2, the north face descended essentially
(displaying all the absolutely necessary, extremely important
features)
in free fall (any motion of a body where gravity
is the only force acting upon it)
, indicating negligible (so
small or unimportant as to be not worth considering)
support
from the structure (approximately 40,000 tons of
structural steel)
below.

 
Stage 3 (4.0 to 5.4 seconds): decreased acceleration, again
less than that of gravity.



....means that an explosion, or a number of explosions, must
have occurred that was powerful enough to quickly remove all
support
from beneath the upper part of the building (below right),
either all at once or incrementally in advance of its descent,
permitting it to descend at gravitational acceleration as a
single unit for the observed period and under the
exceptionless condition required (below left) for
gravitational acceleration to occur....



The building was brought down by explosives.
« Last Edit: 14/05/2016 16:18:30 by Aemilius »
 

Offline PmbPhy

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Quote from: Aemilius
Well Bored chemist, your last post makes just as much sense as your first.... none. At least you're consistent!
A very accurate observation.
 

Offline jccc

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Re: What is Free Fall?
« Reply #145 on: 21/03/2015 08:24:16 »
free fall is rolling with the punches instantaneously
 

Offline Aemilius

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Re: What is Free Fall?
« Reply #146 on: 30/04/2015 19:21:43 »
Chris tells me (privately) that I've had several complaints now so genuine apologies to all for ruffling any feathers (including yours Chris), that was never my intention. From the start all I've really been interested in, all I've really been trying to do, is get to the bottom of it.... and I have now.

Thanks again for engaging me and for helping me sort it out Dr. Calverd, it was a real marathon, and I had fun making the animations too, wouldn't have come up with them otherwise.

I must say though (inhaling deeply) that in view of the overwhelming simplicity of the governing physical principle here involving the Law of Conservation of Energy as applied to a falling body I remain completely baffled as to why there was never any other input by any of the other people here apparently so well qualified to judge the analysis that really should have quickly and naturally led to a simple confirmation or denial by consensus of the veracity of the information conveyed by it as one would normally expect in response to such a fundamentally structured high school level empirically verifiable analysis like this (Reply 143) from such a venerable academic institution as University of Cambridge.... where Isaac Newton himself once held the vaunted Lucasian Chair.

Emile Cole
« Last Edit: 17/12/2015 20:17:13 by Aemilius »
 

The Naked Scientists Forum

Re: What is Free Fall?
« Reply #146 on: 30/04/2015 19:21:43 »

 

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