North Tower Acceleration

[William Seger]

163. Yes, that's exactly what he does

Yes, jesters, I have read and understood Ross' analysis. You apparently have not, just as we found with the Bazant analysis.

The major item in Ross' "energy summary" loss column is "Momentum losses 1389 MJ". He got that number from these two calculations:

If we assume that the upper section comprising 16 storeys falls under a full gravitational acceleration through a height of one (removed) storey, a distance of 3.7 metres we can calculate that its velocity upon impact will be 8.52 metres per second and have a kinetic energy due to its mass and velocity of 2.105 GJ. (Using the figure of 58000 tonnes as detailed in the report by Bazant & Zhou.[1])

...

K. E. of falling sectionfiltered= 16 floors moving at (8.5 m/sec)
K. E. of falling sectionfiltered= 17 floors moving at (4.8 m/sec)
Percentage loss of K.E. = 1-(17 * 4.8/ (16 *8.5) * 100% = 66%

What Ross is doing in that last line is calculating the kinetic energy present in the masses and velocities before and after the collision, showing a loss of 66% of the kinetic energy due to the inelastic collision. So 66% of 2.105 GJ is 1389 MJ, which Ross takes as "momentum losses."

An inelastic collision is one in which the bodies deform and move off together at the same velocity. Momentum is conserved, but kinetic energy is not, because some of the kinetic energy is used to deform the bodies. Now, the specific numbers Ross used for that calculation represent his dubious notion that a huge amount of momentum was transferred to the lower structure, and his dubious low "after" velocity because of that means his calculated kinetic energy loss is dubiously high, but that doesn't matter at all here. It's only necessary to note that Ross is claiming energy losses due to the inelastic collision.

Then, in his "energy summary," Ross lists "Pulverisation of concrete on impacting floor 304 MJ" and "Pulverisation of concrete on impacted floor 304 MJ."

Does that help you to see the problem? As I said before, the kinetic energy lost in an inelastic collision IS the energy that goes into deforming and breaking stuff, including any "pulverisation" of the concrete. That's WHY the kinetic energy is lost. And importantly, because we know momentum must be conserved, we also know that's the ONLY energy available to do that work. Ross can't arbitrarily decide that the concrete is not being pulverized enough and magically direct more kinetic energy there. Furthermore, there isn't any purpose in trying to find more energy sinks like the concrete cracking, some of which Ross alludes to but does not include, because we already KNOW precisely what the total of all those losses would be -- or at least we would IF we did the momentum calculation correctly -- and Ross already showed what he's taking for that.

So, Ross counted 604 MJ of energy twice in coming up with a "Minimum Energy Deficit -390 MJ." And now he has nothing to say about it?

> In any case, it appears Newton's Bit's reply was not even worth a response.



No comment.

> From what I can tell, the main point Ross contributes here, and one that is observed by many others, is Bazant's failure to account for energy absorption and dissipation in both colliding masses.

When Ross says things like that, I can't help but think he doesn't really understand the argument. Ross claims that Bazant "assumes" that all of the energy of the falling mass was present on the impacted floor, and only there, and since that's obviously not true then Bazant's analysis must be flawed. Bullshit; Bazant "assumes" no such thing. He simply calculates how much energy would be required to fail the columns on that floor -- the floor that needs to halt the collapse if it can be halted -- and compares it to the total available. Bazant's answer is that less than 1/8th of the available energy is sufficient to lead to total collapse, even in this best-case scenario. Despite Ross' claim about Bazant's "assumption," that pretty much says to me that all of the energy does NOT need to be there! You want to include the energy that destroyed the falling floor? Fine, then there was four times more than enough to destroy both floors. You want to guess that Bazant got the mass and falling distance so wrong that his available energy was, what -- would half of Bazant's estimate make you happy? Okay, as doubtful as that is, there would still be twice as much energy available than required to fail those two floors. You want to get nit-picky and see if you can reduce it further with a host of minor details? Well, okay, but then it would only be fair to get nit-picky about such things as the fact that the fall probably involved two floors instead of one and that not all of the columns were pushed into buckling so the real collapse required less energy than Bazant's limiting case.

Contrary to your claim, despite all the nit-picking, "truthers" have so far failed to come up with VALID technical criticisms of Bazant's analysis that can quantitatively be shown to reverse Bazant's conclusion.