Antenna and NW Corner Drop Curves: The Detection of Jolts
Drop curves of a point on the antenna and a point on the NW corner, Sauret viewpoint
The Sauret drop curve of the NW corner is shown in blue. It's corresponding velocity curve is shown in purple. The drop curve of a point on the antenna is shown in yellow. It's corresponding velocity curve is shown in green.
If the 2 points were part of a "rigid block" rotating about an axis over the first few degrees of tilt, both the slopes and the curvatures of the position data at any moment would remain proportional to one another. They clearly do not.
There is no relation between slope or curvature between the two positional data plots. Instead they move quite independently, telling us that there is no fixed "rigid block" motion.
Notice the antenna drops about 2 ft slowly (before it has any significant velocity). This is easy to see by looking for the failure point, or release event of each curve and studying the pre-release movement as described below:
ONE APPROACH TO READING DROP CURVES
First, locate the release event. In some frame the velocity will begin to take off, meaning the slope of the velocity plot changes quickly. This is because there is an abrupt change in acceleration. This frame can be called the "release event" or "release moment".
Second, separate the curve into 3 regions: A pre-release region, a post-release region and the region of the release event.
Pre-release motion could be drift, creep. deformation, tilting, vibration or any slower movement which lacks a downward acceleration at a significant percent of g. A careful researcher should trace points in the pre-release region as far back as necessary to discover the earliest motion possible.
Post-release motion has an average downward acceleration of 0.5g to 1.0g. It may have moments of velocity reductions or may not. If so, the momentary downward acceleration between reductions may differ from the average acceleration and should be considered separately. Locations and magnitudes of the velocity reductions may provide valuable information about what is really happening inside the building over the first 12 feet of falling.
The release event Using the velocity graph, curvature at the release point may help determine how quickly the initial failure occurred.
Application of this approach to the Sauret antenna and NW corner drop curves:
We see there is an abrupt change in the slope of the velocity curve that can be traced back to around frame 222. This is the release event for the NW corner, the first moments in which downward velocity noticeably takes off.
The acceleration (slope of the velocity curve) quickly changes through frame 222. The traced point is now falling at 0.5g to 1.0g. There is one measured velocity reduction around frame 250. In frame 250 the positional data shows the NW corner has fallen about 3 ft.
In the pre-release region we can carefully study changes in the positional data as far ahead of frame 222 as we wish, looking for the earliest detectable deformations.
The Sauret drop curve of the black-white transition point on the antenna is in yellow. It's corresponding velocity curve is in light green. We see movement from frame 140, yet the velocity curve does not take off with a 0.5g to 1.0g acceleration until frame 215. The release event is around frame 215.
In the pre-release region we see considerable movement before frame 215. Over 2 feet of downward displacement is measure in the antenna between frames 130 and 215.
In the post-release region we detect one velocity reduction. How far has the traced point dropped when the reduction occurs? It happens around frame 228, when the positional data shows a 3 ft drop.
Detection of velocity reductions in both the antenna and NW corner drop curves.
Notice that both the antenna and NW corner experience a measurable velocity reduction after about a 3 ft downward displacement. It is quite interesting that there is a time interval between the velocity reduction on the antenna and the one for the NW corner, a slight delay between the the reductions, the antenna leading the NW corner by about 20 frames, or 0.3 seconds.
NW CORNER DROP AND VELOCITY CURVE: Independent confirmation of velocity reductions
In a separate set of measurements, the position drop curve of the NW corner (the smooth curve) is shown below
Larger: 
