squirt

• aim compensation
• cue natural pivot length
• endmass and stiffness
• low-squirt cues
• published data
• squirt, swerve, and throw confusion
• straight-in shot with unintentional English

for more information, see Section 4.04 in The Illustrated Principles of Pool and Billiards

aim compensation

How can I easily adjust my aim to account for squirt?

My November '07 and May '07 articles cover aim-and-pivot techniques, which can be used to adjust your aim for squirt.

endmass and stiffness

How does shaft endmass affect squirt and how is endmass related to stiffness?

See Diagram 4 in my February '08 article. People who think extra stiffness is required to produce more squirt are incorrect. Added endmass alone (without added stiffness) produces significant increases in squirt. This supports the theory in TP A.31.

However, "endmass" is related to stiffness. A stiffer shaft will typically be thicker and heavier at the end. Also, transverse shock waves will travel faster in a stiffer shaft, effectively increasing the "endmass." See the paragraph after Equation 4 in TP A.31.

For more information, see NV B.32 - Squirt and the effects of endmass and my August '08 article.

published data

Where can I find published data on squirt values for various cues?

Platinum Billiards's results is the only collection of extensive data I have seen. I've also seen Meucci's video. Meucci is measuring the combined effects of squirt, swerve, and throw, so good squirt numbers are not directly reported, but the video still offers a decent relative comparison between selected shafts. Ron Shepard's squirt paper reports a squirt angle range of about .5 to 2.3 degrees for low- to high-squirt cues, corresponding to a pivot point range of about 50" to 10". Platinum's data ranges over 1.3 to 2.3 degrees of squirt angle and 7.6" to 14.1" for pivot points. I agree Platinum's low-squirt values seem a little high, and the pivot point numbers seem way off; but, again, if their experiments were done as reported, the data is at least useful for a relative comparison.

I have some data available here. My numbers seems to fall in between the ranges reported by Shepard and Platinum.

squirt, swerve, and throw confusion

How can you predict the directions and amounts of squirt, swerve, and throw with various types of shots?

I’ve gotten several e-mail questions concerning Diagram 3 in my August '07 article. Here's the diagram:

Several people have suggested the throw direction is wrong due to collision- or cut-induced throw (CIT). Before giving you my answer, think about it yourself and decide if you think the diagram is correct or not. Also, many people seem to be confused by the real effects of squirt and swerve. I think Diagram 4 from the article (see below) helps clarify things.

I use the phrase "effective squirt" for the net effect of squirt and swerve. Some people like to call this "squerve." My series of articles on squirt covers all of the details of squir and swerve.

Now back to Diagram 3. Throw direction depends on the direction of the relative motion of the surface of the cue ball in contact with the object ball. This direction is affected by both cut angle and spin. I think my January '07 and February '07 articles illustrate the different possibilities quite well. Please refer to them. I think the throw direction shown in Diagram 3 of my August article is appropriate given the amount of English.

Object ball throw depends on cut angle, shot speed, type and amount of English, and the amount of vertical plane spin (draw, follow, stun). My series of twelve articles on throw elaborate on all of these factors. Collision-induced throw (CIT) and spin-induced throw (SIT) are just different names for throw, depending upon the primary cause of the throw, but the effects don't really combine as separate factors.

straight-in shot with unintentional English

What effects do squirt, swerve, and throw have with a straight-in shot hit with unintentional English?

I think there are two possible cases here:

1.) The cue is aligned in the proper aiming line direction but shifted to the left a little, creating unintentionally left English, but the stroke is straight. In this case, the CB will squirt to the right (the amount depends on the cue and the amount of tip offset), the CB will swerve back some to the left (the amount depends on shot speed, cue elevation and ball/cloth conditions), the contact point might be to the left or right of the initial target depending on the relative amounts of squirt and swerve, then the English will throw the OB a little to the right of what the contact point suggests.

1.) The cue is aligned in the proper aiming line direction and the cue tip is aligned with the center of the CB, but the stroke is not perfectly straight, resulting in slight unintentional left English. In this case, the aiming line is now pivoted to the left a little, so the CB will tend to head to the left a little (the amount will depend on bridge distance). Everything else is the same as with "1," but now relative to this new aiming line direction.