I'd like to return to the issue of "free fall/near free fall," as it seems to be the truthers' cleverest trick. Forget the definition of "near free fall" for now. The more fundamental truther claim is, the towers fell "too quickly." I'm under the impression this is one of the more easily refuted claims. If so, is it a matter of some basic physics equations?
As with everything else, there are layers to this one. In order of decreasing absurdity, they look something like this.
1. Faster than freefall. On a quick Google search last week, I found three sites with content originating in 2007 that made this claim, so claims by the truth movement that they've moved on from this assertion are as weak as the claims that they've moved on from pods or the missing 4,000 Jews. The claim is that explosives created a partial vacuum that sucked the buildings downwards. If you're talking to someone who actually needs to hear a physics argument to refute this, give up talking to them right now.
2. At freefall. This is usually backed up by reference to the NIST report, which gives times from collapse initiation to the first exterior panels hitting the ground. Not surprisingly, this refers to free falling debris, which did indeed hit the ground at the time free falling debris would be expected to hit the ground. The collapses were significantly slower than this, and the irrefutable evidence can be found - as the steely-eyed killed of the deep says - in still photos. It's a remarkably poor dynamic argument that can be refuted by a single static picture.
3. Near freefall. Now we get to the heart of the issue, which is that truthers claim that the towers fell slower than freefall, but not slowly enough. This is a classic example of the undefined inequality, where a truther argues that A is less than B, but refuses to evaluate A or B. The simple response, therefore, is to evaluate both, and show that in fact they aren't different. And this is where the argument gets serious, as you'll see from one or two current threads.
The problem here is that neither the predicted nor the actual collapse time is known to great accuracy. Actual times are based on a combination of video evidence and seismic data, because the final stages of the collapse were hidden by dust clouds, and are generally estimated to be in the range 12-16 seconds for the main collapse. Predicted times are more difficult, because the collapse was such a complex event that it is essentially impossible to model. There are various simplifications that can be made to give an estimate of the collapse times, and Frank Greening's papers give the most thorough analysis of these simplifications that I've seen - see
http://www.911myths.com/html/other_contributions.html - but these rely on an understanding of the failure properties of steel that are far from trivial, and on numerical modelling (albeit simple enough that it can be done in a spreadsheet). The result is that the observed collapse times are exactly what they would be expected to be, to within the errors of both the measurement and the model.
Truther responses to this tend to take two tacks. One is to try to repeat the calculations but generate an estimate far in excess of the actual collapse time; Kenneth Kuttler and Charles Beck both do this, but their results are based on wildly inaccurate and unrealistic assumptions about the failure properties of steel. The other is to try and cast doubt on the simplifications used in the model; Major Tom, on this forum, appears to be heading this way. The problem with this argument is that it doesn't offer a line of disproof, because even if we accept these criticisms we're then back to the situation where the collapse is not amenable to modelling. Given that the truth movement is trying to prove that the collapse times cannot be consistent with gravity based collapse, this therefore invalidates their whole argument, but generally they choose not to acknowledge this minor point.
So the answer is, no, there aren't any particularly basic physics equations that help here; it's a complex situation to model, and requires detailed understanding of steel failure mechanisms. I've learned a lot about the subject on this forum, and there's still a lot I'm not up to speed on. However, so far all the evidence is that there was nothing unusual about the speed at which the Twin Towers collapsed, and any claimed evidence to the contrary has been shown to be fatally flawed.
Dave
) is unlikely to remember the sort of real-world experience that's needed for a critical examination of a theory that tries to spread itself around as many disciplines as it can mis-spell. University professors tend to be very much of this stamp, so it's quite possible that, when presented with a line of argument that looks authoritative but doesn't touch on their specialist research area, they'll initially be fooled.
) becomes a calculation of the forces in question, like what Bazant's work involved. Does the force imposed by the upper sections overcome the "resistance" of the lower ones [/rhetorical question]? I realize there are threads discussing this (as well as digressions in other threads not centered on this topic), but my point is that this is the proper way to analyze the whole concept of "path of most/least resistance". 
