short version:
http://www.youtube.com/watch?v=kXNofmrvX3E

long version (shows them setting up):
http://www.youtube.com/watch?v=jcO-pDwzgmk


1st, can any of you engineers or physics people (sorry for lack of a better term), or can anyone else for that matter, please explain what scientific principle is at work here, that allows the guy falling to slow down so quickly in such a short distance.

2nd, why should or shouldnt the upper parts of wtc 1 and 2 have
slowed down in the same way?

3rd, if im wrong about the 2 events being comparable, please point out the
specific distinctions why or why not.

4th, im NOT saying that it is correct to compare the physics of towers falling to the
guy landing on boxes. im just wondering IF they are comparable.

5th, even if it has no scientific value and/or relevance, its still a crazy freakin stunt worth watching (if the guy blows it, he's dead). so watch at least the short version.

:)

6th - if i posted in the wrong forum sorry. i couldnt figure out if it should go in the WTC forum, or here. so i wont be crying about it if it gets moved...


peace

The key thing here is to slow down as slowly as possible. When the guy was just about to hit he was travelling at a certain velocity which gives his body an amount of momentum. The key to surviving such a fall is to absorb this momentum as gradually as possible.

I think the technical term here would be impulse, you seek to minimise the amount of force imparted to the person by increasing the amount of time it takes to absorb the energy. Cardboard boxes folded up do a reasonable job of this in several ways, they absorb energy while deforming but their closed nature also means air has to escape. A commercial version is this which uses only air to decelerate the stuntman. By controlling how much can exit at one time you store energy by compressing the air.

They did, I will explain below

Imagine several sets of these boxes, suspended in air (somehow, it's irrelevant) at intervals of 115ft, then the guy jumps from 115ft above the top set. When he impacts the first set of boxes they will absorb a certain amount of energy and therefore slow him to a certain speed (we're assuming for a second they cannot stop him completely). If they do not slow him to practically zero he will be accelerated by gravity to a greater speed over the next 115ft fall and impact the second set of boxes with more energy than before. Assuming the initial set of boxes could not completely stop him, no further sets of boxes will as long as he has the 115ft to gain energy in falling.

This situation is analogous to the situation in the WTC towers. Ignoring the initial failure we can posit a 1 storey drop which gives the upper section a certain amount of kinetic energy, if the columns on the next level down can not completely absorb this energy they will fail and the top section will not only increase in mass but in energy before striking the next floor.

In reality of course it's much more complex, the initial failure was not a symmetrical 1 floor collapse, the next floor's columns were not all involved in absorbing energy, some of the mass was ejected in the collisions (20-50%) and the upper section rotated. This makes analysis much harder and there's been some criticism of Bazant's model over at JREF recently. I hope however it illustrates how the forces involved are applied.

Yeah it is kinda shocking how quickly the boxes collapsed, I suspect he received quite a serious impact regardless.