Mass v. Mass

The AE911Truth presentation presents a “story problem” when discussing how the towers fell. It’s accompanied by this illustration:

It shows the upper section of one of the Twin Towers supported by a crane over the lower section. Another crane holds an identical upper section over thin air and the viewer is invited to guess which upper section will hit the ground first.

If the 15 story section is falling at free fall speed…
  • All of its gravitational potential energy is converted to Kinetic Energy (movement)
  • It is not available to the work of “crushing” the building below!
  • It would have to slow down in order to do any othe work, i.e. “crushing 80,000 tons of structural steel below.

Richard Gage, the founder of AE911Truth, like to use a version of this in his speeches, using three specially-made cardboard boxes. Both the boxes and this drawing are highly prejudicial and seek to heighten personal incredulity in the viewer. I would like to see the crane that could be built that much taller than a 110-story building and be able to support the mass of 15 floors of that buildings. And Gage’s reduction of the complexity and scale of the WTC building structure into cardboard boxes is worthy of a top 10 AE911Truth mistake itself.

There are many errors in this story problem: the upper section wasn’t moving at “free fall speed,” for example. Pictures abound of debris falling along the side of the building at a faster rate of acceleration than the upper section. However, by asking its audience to think about the upper section “crushing 80,000 tons of structural steel below,”  AE911Truth wants you to consider this interaction as one of Mass vs. Mass. Of course the greater mass should win over the lesser mass of 15 stories, right?

Not at all.

How A Building Works

High rise buildings are built to support their own mass (which does not change), the mass of the floor’s occupation (which changes gradually but constantly), and to resist lateral forces (like the wind hitting the building or an earthquake). These (and other forces) are sometimes called loads.

Buildings do this by using structure to distribute these various loads safely down to the ground. If there is a part of the structure that might experience bigger loads, the structure will use various time-tested systems to distribute that greater load throughout the structure so that no single part is stressed beyond its ability to do its work.

The building codes of various municipalities tell construction specialists a great many things about how they can build their buildings. Part of the code tells them how much their buildings must be able to accomodate when it comes to various stresses and loads. The WTC towers and Building 7 were no different. If a strong wind were to hit those buildings, they would have been expected to transmit that load safely through their structure and down to the ground. A building that could support its own mass, the gradual back-and-forth mass of its occupation, and the sudden loads from wind and earthquake is a building that is working well.

Static Loads and Dynamic Loads

Static loads don’t move and they don’t change. They are constant stresses on the structure. Dynamic loads do change. The mass of the building itself is considered a static load. Both the gradually changing load of the building’s occupation and the sudden loads of wind and earthquake are dynamic loads.

And dynamic loads are the real problem for a building’s structure. My favorite “story problem” of this is a brick and your head. If you were to place a brick carefully on your head, the structure of your body would easily distribute this gradual dynamic load through your skull and down through your skeleton to the ground. After that, the load of the brick becomes static, and your body’s structure has no difficulty in continuing to transmit that static load to the ground.

But lift that brick just an inch from your head and then drop it. The dynamic load from the brick now will give you a painful start and maybe even raise a bump. Lift the brick even further — a foot, six feet — and the brick could seriously damage your head. It could easily kill you if it was high enough.

And yet it is the same brick! It is the same mass. Why is there such a difference in the load being transferred to your body’s structure?

The brick is being accelerated by gravity. The further the brick falls, the more time gravity has to accelerate it, and gravity doesn’t need long at all to release  the potential energy in even this small amount of mass as a lethal blow.

The Collapses of the WTC Buildings

The story problem above compares the mass of the section above to the section below the impact zones. What truly matters is the ability of the structure below to redistribute the dynamic force being delivered to it by the mass that’s falling.

For example, if a brick falls from far enough, the structure of your skull won’t be able to redistribute that dynamic load before the structure breaks. It won’t matter if you just had a titanium hip replacement, say, or a new knee put in. The skull can’t cope with the dynamic load, and it tears apart before it can transmit the load to the new hip or knee.

The same is true for the mass of the building section above and the structure of the section below the impact zone. If the mass of the section above delivers a dynamic load that’s too large for the structure below to cope with, the structure below is going to tear apart before it can redistribute the dynamic load further down the building.

And the distance the upper section has to fall isn’t very large at all. A paper released shortly after the attacks on 9/11 showed that once the sections above the impact zone had fallen a single story, the dynamic load they had to transmit exceeded the strength of the structure below by an order of magnitude. The upper section, to turn the phrase around, had brought a gun to a knife fight.

So the story problem misrepresents the situation at the towers tremendously. The mass of the section below doesn’t matter. It is the structure that is going to distribute the dynamic load, and the structure below couldn’t, not by a long shot. It doesn’t matter that the mass below the impact is so much greater than the mass above. The force from the mass above is being increased by gravity to the point that the structure was unable to deal with it.

By representing this interaction as Mass v. Mass, AE911Truth conceals the true complexity of the problem. They recently obtained non-profit status as an educational organization, but this framing of the WTC collapses hinders actual education about these events. This basic misconception isn’t something that can be explained very quickly. But when understood, it’s clear that it is a crucial way AE911Truth does not understand what is happening before their eyes. The sad thing is that they are actively working to keep others from understanding it as well.