The South Tower's Top Disintegrated As it Fell
- The curvature of the wall shows about 30 stories above crash zone
had shattered less than 2 seconds into the collapse
- Top did not rotate about fulcrum,
rather it rotated freely about a changing axis.
- Angular momentum of the tipping top vanished.
Only the disappearance of the moment of inertia through the
breakup of the top can explain this.
NBC video
Frames of NBC video at one-second intervals: