American Assoc. of Physics Teachers Chicago Meeting Paper (2/15/09): "Showing South Tower of WTC Collapsed from Forces Stronger than Gravity"

Crockett L Grabbe, SeaLane Research & Consulting 319-338-4338,


Physics students can be taught a straightforward yet very powerful application of Newton's principles of motion. It is one of direct application to the debate on the issues on 911, and helps students get a grasp on scientific facts in that debate. That application is showing that the forces that ripped the South Tower of the World Trade Center apart were about an order of magnitude larger than the force of gravity. The application could be easily taught in classes covering mechanics from Newton's principles of motion.


Slide C1:  
South Tower before the collapse 
The S Tower (on the LHS) at 9:59 AM, 56 minutes after the plane collision, 
almost at the time the collapse initiates.

Slide C2:  
S Tower collapse 4 secs later than C1:

o White horizontal ejections (which I call "squibs") are coming out E side, 
with pulverized white concrete ~ 2 floors BELOW the fires from the plane

o The top segment of the S Tower is leaning 4-5 degs

o There seems to be a crack in lean where smoke is ejecting

Slide C3:  
S Tower collapse 0.75 secs later than C2

o The squib front has moved ~40 feet in t=3/4 sec, so is travelling ~ 40 
mph AFTER expending considerable kinetic energy to break thru the walls

o The Tower lean has increased to 9 degs

o The crack appears to have become larger & emit more smoke

**Since energy E & momentum p are conserved, E & p of the squibs must have 
originated somewhere.  Another p must be opposite to the horizontal 
direction they are travelling!

**Did E & p come from chemical E released in explosions in the horizontal 
direction?  There must be a large source of E to break thru walls.

Slide C4:  
Distant view of the Towers 1 second later than view in Slide C3 

o A massive gray cloud expansian has occurred at the bottom of the top 

o A drop in top of the tower has occurred -- that is because the concrete 
of the top segment is being pulverized at bottom of the top segment (it is 
gray because the concrete is saturated with smoke from the fire of the top 

**Conservation of mass effectively PROVES top is dropping from pulverizing 
concrete (producing gray smoke) at the bottom of the top segment.

Slide C5:  
Distant view 0.75 secs later (where all HELL is breaking loose!)

o In 3/4 sec new white squibs have moved out over 100 ft, so are 
travelling ~ 50 m/s or ~ 100 mph!  What produced this large horizontal p?

o A sudden break has occured in the S Tower top segment corner, & right at
the break the top segment has shifted ~ 50-60 ft to the right & into page! 

o The top of the S Tower drops another ~ 50 ft.  It is losing large 
quantities of its mass in those gray dust clouds.

**A huge jolt of E & horizontal p is imparted to the top segment.  

**The MAXIMUM distance gravity force could move it is 0.5gt**2 = 9 ft in 
the vertical direction, and that is ONLY if we ignores all the E required 
to break the 2 parts of the edge apart!

**It in fact moves ~ 50 ft horizontally after the break, which implied
**A force > [probably >>] the force of gravity caused this shift!

** Undergraduate mechanics student can measure this from the photos in 
a lab, and deduce from elementary mechanics F(horizontal).  They can do
what NIST FAILED to do in their 2005 Report and deduce from their own
calculations that the NIST conclusion that the S Tower collapsed on its own 
from damage by planes & fire is WRONG!

Slide C6:  
Distant view 0.25 secs later 

o In just 0.25 secs the large E & p imparted still causes more rapid 
change.  These changes provide another datapoint to estimate F(horizontal)

Slide C7:  
Analyzing the physics of horizontal forces 1 

Slide C8:  
Analyzing the physics of horizontal forces 2 

Slide C9:  
Closeup perspective of the collapse from N direction 

o The top segment is falling almost S, and looks like it will topple off.

o It completely disappeared into the gray smoke clouds instead!

o The white & gray clouds are clearly distinct, coming from the separate
top & bottom segments
o Significant p has been imparted horizontal to pieces of cladding coming 
from the bottom segment.  The pieces have moved up to 70 ft away from 
tower in a short descent downward.

Slide C10:  
Distant view of Towers at 1 sec later than Slide 9 

o The top segment has over 50% gone all up into the gray clouds that are 
expanding out.  

o Notice the bottom segment of the Tower is undeterred if nothing further 
happens!  It is stable, and the collapse would cease.

Slide C11:  
Collapsing S Tower seconds later 

o Notice a squib emerging later below the collapsing part in the collapse 
of S Tower.  

o Notice the bottom part of the Tower is undeterred by explosion above.
Further release of breakup energy is needed to sustain the collapse, 
otherwise the lower segment would remain standing!

o Notice the small comet moving at high speeds atop the dust cloud on the 
LHS.  Streaks ~50 ft in 1/32 s exposure time = ~1600 ft/s or 0.3 mi/s!
Air resistance very important in equs. of motion.
It either had initial upward velocity, or it arose above the tower.

Slide C12: 
Conclusions & Bibliography 

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