But the stuff didn't break when it hit the ground. It pulverized in mid air. And it is NIST that says the structure encountered "very little resistance".
There's a third option, you know -- pieces breaking because they hit other pieces, or parts of the building that hadn't yet collapsed or were falling slower. Crumbling is an expected part of the collapse itself.
And yes, you can tell plenty about clouds from their shape. A mushroom cloud, such as the one where WTC1 just was, is a very specific phenomenon. Very interesting physics.
Mackey, what makes a mushroom cloud do its thing, and why is there one in the picture of WTC1?
I'm going to try an olive branch here. This is a fair question, and it also lies within a field that I've studied extensively.
The "mushroom cloud" shape is governed by a fluid dynamical phenomenon known as
Rayleigh-Taylor instability. What it means is that if you have a quantity of a lighter fluid trapped under a heavier fluid -- typically, because the fluid below is heated -- then because this is a metastable configuration, any* small deviation in the lighter fluid's boundary will grow and amplify, leading to a characteristic "bubble" shape. As this bubble moves upward, fluid along the boundary gets rolled along, creating one or more
vortex rings. It is this
vorticity, where vorticity is defined as the
curl of the fluid velocity, that gives rise to the shape.
While this is specific physics, it is also extremely common in nature. Atomic explosions typically create strong examples because the fluid heating is sudden, extreme, and relatively symmetric. However,
any heat source can do this -- volcanoes and forest fires, or even your barbeque if you're not careful. You see similar effects in mixing ocean layers of different salinity, and in geology in the formation of salt domes. It is in no way unique to explosives, those merely give us a fairly ideal example.
Atomic bombs don't always lead to mushroom clouds, either. Those exploded very high in the atmosphere will not, nor will those exploded deep in the ground (necessary depth being a function of power). One of the pictures you selected shows such an underground explosion. In this case, much of the heating is blocked by the ground, and the cloud effects are dominated by geology and solid kinematics rather than fluid properties.
In the WTC tower collapses, you would expect to see this effect, but the complete situation is very, very complicated. At the moment of collapse, a large volume of heated air would escape or be expelled from the structure, and this air would rise convectively as described above. But there are numerous other things going on:
- Also as the tower collapses, there will be a pistonic effect as air is sucked in behind the roof. This will lead to more vortex formation -- but vorticity of the opposite sign. This vorticity may interact with the convecting, heated air in extremely complex ways.
- There is a slow, but large and steady plume from the burning building, creating local updrafts prior to collapse.
- There is a significant crosswind, as well as local gusts caused by eddys around other buildings.
- The tower is hemmed in fairly tight by other buildings, which will have a significant impact on vortex ring formation.
- Last and not least, you have TWO of these buildings burning right next to each other, not one in a clear area.
This is about as complicated as a fluid flow problem gets. It is natural to expect
some features to resemble convection, and others to be different. And that's pretty much what we got.
This is why what something "looks like" is not sufficient to base a hypothesis. It's too imprecise. Does it look 90% like a "mushroom cloud?" 80%? 50%? What does that even mean? The pictures can't tell the whole story. The story that they do tell is consistent with the official story. Doesn't
prove it, mind you, but it certainly isn't evidence of anything else.
*: Whether or not this is expected to happen quickly or slowly (or effectively never) is a function of the Rayleigh Number, a dimensionless constant that depends on gravitational and viscous forces, thermal effects, and the size of the phenomenon. For the WTC case, the number is large and convection sets in very quickly.
