DGM
Skeptic not Atheist
Thanks for the clarification. I've been struggling with the friction end of the collapse (I don't know why) as of late. I remember now these figures.I have no inclination to read back on your current exchange with C7, I just want to point out one thing: The potential energy of the erected buildings, liberated by the collapse and briefly turned into KE before finding its final resting place on the ground, mostly did work to deform and fracture material (yep, practically all the pulverisation is explained by that), but pretty little of it turned into heat. That heat translates into a very tiny increase of temperature. To put some numbers to it in a thought experiment: Strip the tower of everything that is not steel, so you are left with the the steel frame, floor decking, rebar. The center of mass of that steel structure would be at maybe 40% of the height of the tower, or 167m. A given kg of steel would thus, on average, have a potential energy of PE = m*h*g = 1kg * 167m * 9.8m/s2 = 1637 J
Iron has a molar heat capacity of 25.1J/mol/K. 1 mol of iron is 0.055845kg, so heat capacity by mass is 450J/(kg*K)
If you apply 1637J of heat to 1kg of iron, you warm it by 1637J / 450Jkg-1K-1 = 3.54°C.
Since most of the potential energy in fact goes into other energy sinks, the building material warms up by much less than 1°C on average.
It is of course possible that, through random distribution, very small bits heat up momentarily by much more than that, but reaching the melting point of anything interesting is exceedingly unlikely. That is simply not a way to create high temperatures. (part of the reason is that collision velocities remained rather low; final speed of the collapse front was under 100m/s. I'd sooner believe that the plane crashes may have melted or vaporized very small amounts of perhaps aluminium).
That leaves us with occasional sparks created by friction, but overall, spheres created from mechanical work of the collapses would be totally insignificant in the masses of dust and debris.
Every once in a while I need a slap of math to bring me back.