How much and in what manner does a cue shaft deform and vibrate during and after a shot?
Here are some excellent super-slow motion videos illustrating cue vibration effects with sidespin shots:
- HSV A.25 – Cue flex and vibration due to firm stroke with sidespin
- 2008 testing of a prototype cuttlefishcues carbon fiber shaft showing how a stiff shaft does not deflect away from the CB as much, and returns to the CB quickly (risking a double hit)
And here are some with follow and draw shots:
The cue also vibrates longitudinally (very quickly) with every hit, even center-ball. See:
Some additional examples of accelerometer measurements can be found here:
The amplitudes, frequencies, mode shapes, and durations of cue vibration are big factors in determining the “hit” or “feel” of a cue.
There several types of elastic waves that travel through the cue during vibration. One type is called the “longitudinal” (down the length of the cue) or “compression” waves. The speed that these waves travel down the cue is directly related to the speed of sound in the cue material. This wave travels very quickly from the tip to the joint and butt end and back while the tip is in contact with the cue ball. If it didn’t, the entire weight of the cue would not come into play during the tip-CB collision (but it does).
The other type is called “transverse” or “lateral” or shear elastic waves that corresponds to deflection of the tip perpendicular to the shaft (in the squirt direction). Transverse shear elastic waves move much more slowly than the longitudinal compression waves. Their speed depends on the lateral stiffness of shaft and cue. The transverse wave affects how much “effective endmass” a shaft has, and therefore how much squirt (cue ball deflection) the shaft produces with a off-center hit. The transverse waves also contribute to the cue flexing and bending (in different modes or shapes) visible in the videos above.
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