Just a few points on the physics aspects of Jones' presentation.
Quote from version77:
Q: Can anyone prove the steel used in these buildings was actually as
strong as believed?
As strong as believed by who? The general properties of structural steel are
pretty well known by now, as one might imagine.
There's no reason that I know of to believe that the steel in the towers was
any weaker than other structural steel of similar quality. I haven't heard
anything like that suggested by anyone.
Of course, there is no need to assume that that was true, in order for the
buildings to have collapsed as they did.
And can anyone prove without a doubt that the temperatures did not
get hot enough to melt it?
It's
very unlikely that the temperatures ever got hot enough to melt
steel in those fires. Of course, one can't prove that this didn't happen. But
it would take temperatures near 1400 C to melt the steel. Jet fuel burns far
cooler than that and the flammable materials inside the towers would be
expected to burn still cooler than the jet fuel.
As far as I know melting of steel structural support beams is never, never
observed in ordinary fires that happen in steel frame buildings. If molten
steel
actually had been found in the rubble very shortly after the
collapse, it
would be pretty strange.
The pictures of supposed molten `steel' that I've seen published by the
conspiracy theorists, including those published by this fellow Jones whose
presentation is on the tape, are problematic as far as I'm concerned because
they don't allow for an easy determination of what the substance is that we
are looking at.
Contrary to what the conspiracy theorists would like to suggest, it does not
follow that some apparently molten material observed in photographs of the
rubble to be glowing cherry red, orange, or yellow, is molten structural
steel. There can be other explanations.
Many people who should have known better, but who nevertheless commented on
the fires in the trade centers in the early days after 9/11 were confused:
both about the temperatures achievable in such fires and about the properties
of steel. Conspiracy theorists have seized on some of the ill-informed
comments that were made, and used them to suggest that the official story was
that the steel was
melted by the fire and that the melting is what
caused the collapse.
In fact, in that context, the question whether the steel became hot enough to
melt is just a red herring. It's completely beside the point whether or
not the fire was hot enough to melt steel.
A rule of thumb is that the strength of structural steel is reduced by 50% at
a temperature of 550C. Steel samples loaded symmetrically to about half of
their load bearing limit, and heated uniformly to 550C will fail pretty close
to the time when they reach 550 C.
This temperature is clearly well below the melting point.
The time to failure for a load bearing beam in real conditions of a fire can't
be predicted so simply.
It depends in a complicated way on the temperature distribution throughout the
steel and on the distribution of the load which is borne by the beam. If hot
spots are produced in some parts of a beam, say on the corners or outside
edges, it's quite possible that it would fail well before the time when the
whole thing reaches 550 C. Steel in hot spots can become overloaded first, and
begin to deform plastically. In turn, the plastic deformation in the hotter
areas increases the stress on the cooler steel in the rest of the beam, and
when the cooler steel is strained past its elastic deformation limit it begins
to deform plastically too, and this process then leads eventually to fracture.
Most of this can be tested experimentally on actual structural steel, and it
has been. Some good data on fire testing of structural steel is available
here.
http://www.mace.manchester.ac.uk/project/research/structures/strucfire/DataBase/TestData/default.htm
And can anyone prove the towers were built as they say they were?
I didn't think so.
Well there's every reason to believe the towers were built as the builders say
they were, I should think, at least. I don't know of a reason to disbelieve
it.
Jones' presentation on this video is not very impressive as far as I'm
concerned. There simply isn't very much in the way of detailed discussion of
any the physics of the collapses there. He describes how he made a calculation
of the floors `pancaking' based on `conservation of momentum' and found that
they couldn't possibly come down in 10 seconds. But he doesn't ever show us
this supposed calculation, and he makes a very obvious blunder at this point.
10 seconds is approximately the time from the initiation of the collapses on
the videos, to the point on the seismic evidence at which the first signal is
seen. That first signal would correspond to the time when the very first
pieces of material from the towers first begin to hit at ground level.
These first pieces are
presumably some of the exterior panels of the
building, based on a viewing of the collapse videos, though since we don't see
them hitting the ground, we can't be sure of that.
The panels most likely were detached from near the level where the tops of the
buildings appear to hit the bottoms of the buildings, at the initiation of the
collapses. If that were true, it would mean that the panels started falling not from
roof level, but from lower down on the towers, so that they would have a
correspondingly shorter free fall time.
The collapses are not anywhere near complete at 10 seconds, and it's very hard
to actually see when they were complete. You really can't tell how long they
took from watching the videos, and it's hard to say when the seismic evidence
ends exactly, as it tails off gradually. On some of the video and photographic
evidence, it seems that pretty large parts of the cores of the towers were
still standing as late as 25 seconds after the initiation of the collapse.
Speaking purely as a physicist, IMO Jones points out some interesting apparent
anomalies, but is not on the whole very convincing. I find the sloppiness on
basic facts of the collapse, that I've pointed out exists in his discussion,
to be very odd in a physicist who has supposedly studied the collapses in some
detail. This in turn makes me doubt a lot of the rest of what he has to say.
