The first 6 pics (beginning with the ball touching the rail) show the ball on the same straight line.Dr. Dave's line is a more accurate representation of how much the object ball curved imo.
The angle of the picture does not allow for accuracy when you make the line follow the path through the ball at rail and the ball in the first frame because the object ball jumps off the rail.
The ball curving so late must mean John's balls and/or cloth are very clean/slick.
pj
chgo
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