Why is a 1/2-ball hit (30° cut angle) so useful?
The “natural angle” effect associated with a half-ball hit is one of the most important principles in pool and billiards. It is the basis of the 30° rule, which states that for a rolling CB, the carom angle is very close to 30° for all cut angles between 1/4-ball and 3/4-ball hits (not just a 1/2-ball hit). This gem is the single most important and useful principle in pool, especially when used in conjunction with the peace-sign technique.
Many additional resources, with lots of illustrations, examples, and video links related to these principle, can be found here:
- 30° rule resource page (containing many additional resources and video demonstrations of how and when the rule is useful).
- trisect draw-shot aiming system for 90° draw principle.
- collection of instructional articles on this topic:
- “The 90° rule: Part I – the basics” (BD, January, 2004).
- “The 90° rule: Part II – breakup and avoidance shots” (BD, February, 2004).
- “The 90° rule: Part III – carom and billiard shots” (BD, March, 2004).
- “90° and 30° rule review” (BD, July, 2004).
- “The 30° rule: Part I – the basics” (BD, April, 2004).
- “The 30° rule: Part II – examples” (BD, May, 2004).
- “The 30° rule: Part III – carom vs. cut” (BD, June, 2004).
- “90° and 30° Rule Follow-up – Part I” (BD, February, 2005).
- “90° and 30° Rule Follow-up – Part II: speed effects” (BD, March, 2005).
- “90° and 30° Rule Follow-up – Part III: inelasticity and friction effects” (BD, April, 2005).
- “90° and 30° Rule Follow-up – Part IV: sidespin effects” (BD, May, 2005).
- “90° and 30° Rule Follow-up – Part V: the final chapter” (BD, June, 2005).
- “Draw Shot Primer – Part I: physics” (BD, January, 2006).
- “Fundamentals – Part V: CB position control” (BD, January, 2009).
- “Fundamentals – Part VI: CB control examples” (BD, February, 2009).
- summary article from Bob Jewett (BD, November, 2000).
- 30° rule and peace-sign technique one-page summary and the angle template.
- NV B.6 – Mike Page’s half-ball hit gems (part 1, part 2).
- Math and physics analyses: TP A.1, TP A.2, TP 3.3, TP A.4, and TP A.16.
The 1/2-ball hit is a common shot, especially in the game of 9-ball, where you need to move the CB around the table a lot. With a 1/2-ball hit, the CB easily be given enough speed to travel significant distance. The CB’s motion can also be killed fairly easily with a 1/2-ball hit. Also, sidespin is very effective off the cushions with a 1/2-ball hit. For thinner hits, the faster ball speed reduces the effect of the sidespin; and for fuller hits and the resulting slower speed of the CB, the spin doesn’t grab as well, especially on new cloth.
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