I saw a similar article on a BBC site shortly after the attack, which was devoid of ifp but characterized all the various events in terms of Joules.
I explained to my intro physics class as Newton's 2nd law problem. Under normal circumstance the 109th floor supplies an upward normal force to the 110th floor to counteract the 110th's downward weight mg. But when the 110th starts to fall the 109th must supply an ADDITIONAL force ma to decelerate the falling 110th floor to rest. This additional force exceeds the design requirements of the 109th so it begins to fall, and the problem only gets worse as each additional floor adds to the mass and pancakes the whole way down. Of course the physics is the easy part. Trying to explain it to a class as a cool dry physics problem is the hard part. Nat > > The 2001 November issue of Scientific American contains data on page 15 > about the energy released in the attack on the World Trade Center > towers and their collapse. Citations for the work are contained in the > sidebar in which this information was presented. > > Despite the name of the magazine, the units worked in include "feet", > "pounds", "gallons", "tons", "mph", and "btu"s. They then pull off a > Hail Mary play and convert the whole mess to joules. But just > centimeters from the goal line they turn around and pass the ball > backward to "tons of TNT". Nice science but lousy choice of units, > except for the joules. I feel yet another letter to Scientific American > coming on. > > The main categories break down as follows: > 2 TJ collapse of the towers > 5 TJ explosion and burning of jet fuel > 9 GJ kinetic energy of the two jets > Personal aside: most experts are saying that it was the heat from the > fires, weakening the steel, that caused the collapse. Essentially then, > the jets were used as flying bombs; had they been nearly out of fuel, > the disaster would have been less exothermic. > > Thus the kinetic energy of the jets provided just over 0.1 % of the > energy released in this attack on humanity and civilization. > > Jim > > -- > James R. Frysinger University/College of Charleston > 10 Captiva Row Dept. of Physics and Astronomy > Charleston, SC 29407 66 George Street > 843.225.0805 Charleston, SC 29424 > http://www.cofc.edu/~frysingj [EMAIL PROTECTED] > Cert. Adv. Metrication Specialist 843.953.7644 > > >
