How do you account for throw with a stop shot with sidespin?
To stop the cue ball using sidespin, there must be a cut angle. In other words, the cue ball must hit the object ball slightly off center as if you were going to “cheat” the pocket (e.g., see NV 5.7). If you are aiming the shot straight-on, cue ball deflection (squirt) will automatically create the cut angle (see NV 4.13 for a description and illustration of squirt). With a cut angle, if there was no sidespin the object ball would cheat the pocket and the cue ball would drift along the tangent line. With left sidespin, squirt causes the cue ball to deflect to the right, creating a cut angle to the left. However, the object ball would be thrown back to the right (due to the left sidespin) towards the center of the pocket. Because the cue ball throws the object ball right, the object ball pushes back on the cue ball to the left, counteracting the expected tangent line motion to the right. Therefore, the cue ball stops in place. “90° and 30° Rule Follow-up – Part IV: english effects” (BD, May, 2005) doesn’t address this issue directly, but the information in the article is relevant.
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