This experiment was inspired by a more sophisticated test that Dave Tutleman performed on a golf shaft. (see v=vjGqZGiYGbs on YouTube) In my case the butt of the rod was rotated by hand using the rollers on a spine finder. As a result my rotation rate was much more sporadic than Dave achieve with the golf shaft clamped in a machined spin indexer device. However, even though the implementation of the butt rotation used here was a bit crude, the end result is the same as for a rotating golf shaft.

During this run the butt of the rod was rotated about one and a half cycles while the tip of the rod was vibrating in a slightly tilted whirling plane that resulted from an imperfect release of the shaft to start it vibrating. Dave mentioned he used an archer-like string release to eliminate any sidewise push of the tip at release. My finger release was not exactly vertical nor push free, and the tip of the rod tends to follow a slightly elliptical whirling path as it vibrates in a plane that is a bit off the vertical. However I think that you can see that path did not change appreciably as the butt of the rod was rotated.

The interesting result shown in this experiment is that rotating the shaft about its long axis has little or no affect on the vibrating tip path. This indicates that the vertical force from gravity dominates any twisting effects due to spine, and thus the tip tends to follow the same path independent of the butt is rotation angle. In casting the tip force from the line would do much the same thing and keep the tip going in a nominally straight line even though the wrist rotation might rotate the butt along its long axis.

The same would not be true for a wrist rotation that caused the butt to change planes. That would cause the tip to travel in a curved path and cause tracking problems that would affect the line path depending on how big the plane change happened to be. However, as shown here if the rod just twists about it long axis there will be little affect on the resulting tip path.

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