Re: [Vo]: Re: No Thermite ?

[Stephen A. Lawrence]

Nick Palmer wrote:
I do not think they went down in freefall,  after a few seconds the rate 
looks like it nearly stabilises as the resistance from the undamaged 
structure below just about cancels the acceleration of the mass above - 
I suspect this figure of 9 or 10 seconds need to be examined from the 
videos and the "free fall time" needs to recalculated...

If it "pancaked" down, no matter what the cause, it should have fallen 
at nearly free-fall speed.  By "nearly" I mean within a second or so, 
top to bottom.  This is simple physics; I worked out part of it in an 
earlier email to this list -- enough to see what the result looks like. 
Anyone with time on their hands and an understanding of x = (1/2)at^2 
should  be able to carry it through to the bottom.  The result may not 
jibe with intuition, so I found it a worthwhile exercise to at least start.

The "hesitation" at each floor before it gave way should have been 
miniscule, simply because as the mass falls, the next floor it hits will 
either break away at (or before) the moment of maximum stress, /or/, if 
it survives the moment of maximum stress, it won't break and the 
collapse will stop at that floor, because after the initial shock the 
stress on the supports declines.  If the maximum stress doesn't break 
it, smaller stresses won't either.  The moment of maximum stress comes 
when the shock wave from the impacting mass reaches the supports, which 
is essentially instantaneous: the shock wave travels through the 
material of the floor at the speed  of sound, and it doesn't have very 
far to go.

So, again, whether the demolition was controlled or uncontrolled, caused 
by an airplane, thermite, a nuclear bomb, or the Tooth Fairy, the fall 
speed should have been very much like what we see in the videos.

Something else worth pointing out:  WE CAN'T SEE THE COLLAPSE in the 
video.  We can see the cloud coming out of the building, which shows 
where all the windows have blown out.  But, the floors were falling 
/inside/ the building, and we can't see them fall -- we can only see the 
results of the fall.  It is quite conceivable that the falling mass 
inside the building actually "leads" the cloud and flying debris we see 
on the outside of the building by several floors.



Nick Palmer