Of Billiard Balls and Executive Toys

Earlier, some commenters brought up the billiard ball theory, from mechanical engineer Judy Wood. It is called this because she compares the collapse of the World Trade Center towers to dropping a billiard ball off of the roof. The entire starting premise of this is of course false, since the collapse did not start at the top, and continue all the way to the ground, but knowing this, we will continue on.










She then argues, that in reality we have to look at this as a series of 110 billiard balls. Each billiard ball falls to the floor below it, where it conveniently comes to a complete stop, and then another billiard ball begins to fall, starting from a complete stop, coming up with a leisurely 87.9 to 96.7 second collapse. This is of course ridiculous.










Buildings like this are engineered to hold the static weight of the floors above them. This is several orders of magnitude less than the force exerted by the floors falling on them. This is analogous to holding a bowling ball in your hand, versus dropping it on your foot. I guarantee the second example will get your attention more than the first. There is absolutely no reason to believe that a floor would absorb the tremendous force of the floors above it slamming into it, wait a minute, and then collapse under the significantly less static weight which is now being exerted upon it. Rather, it would collapse immediately under the tremendous force of 300,000+ tons of building hitting it, just like a football linebacker stepping on a soda can, and then pass along its additional weight to the floors below it.

Ironically, the easiest way to describe the physical phenomenon, is listed on Ms. Wood's website on this topic, the executive toy known as "Newton's Cradle".











Click here for an example of how it works.

This demonstrates the principle of momentum. If you drop a ball on the left hand side, a ball on the right hand side swings up. With more force (two balls) two balls swing up. Note that this happens instantly, the momentum is passed through immediately to the next object, just as one floor would to another. The balls don't stop and think about it for a minute before swinging up at a slower speed. Of course this is the extreme example, with perfectly elastic balls, but it makes the point. In the collapsing towers each floor would provide some drag, like pushing a heavy cart through mud rather than on a concrete path, but in no way would it stop it. This is why the debris shooting out to the side can be seen falling faster than the towers itself.

On her website Ms. Wood brings up the topic of momentum, and then in an exceptionally convenient, and completely unscientific manner, just assumes it away.

I wish I could just assume away the fact that there was an attack on the World Trade Center in the first place, 3,000 people would still be alive, but unfortunately it doesn't work that way.