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David Alciatore ("Dr. Dave") ILLUSTRATED PRINCIPLES The 30 rule

Summary: David Alciatore ("Dr. Dave") ILLUSTRATED PRINCIPLES
The 30 rule
Part I The Basics
Note: Supporting narrated video (NV) demonstrations, high-speed video (HSV) clips, and
technical proofs (TP) can be accessed and viewed online at billiards.colostate.edu. The
reference numbers used in the article (e.g., NV 3.8) help you locate the resources on the
If you don't know the 30 rule yet, learning it can truly transform your game. Like the 90 rule,
presented in my previous series of three articles, the 30 rule helps you predict the path of the
cue ball after impact with an object ball. This is a very important skill to have for helping you
prevent scratches, plan break-up and avoidance shots, and execute carom and billiards shots. It
is also critical in being able to play position (the skill that separates the great players from the
good ones). It always surprises me how few people know this rule. Also, it is shocking to me that
few books on pool and billiards give adequate (or any) coverage of this principle.
As shown in my previous three articles, the tangent line and the 90 rule are useful for
predicting the path of the cue ball when it strikes an object ball with no topspin or bottom spin
(i.e., for stun shots). However, with many shots the cue ball is rolling (with topspin) by the time it
strikes the object ball. So for many shots, the angle between the cue ball and the object ball will
be less than 90. A useful rule for predicting the path of the cue ball when it is rolling is the 30
rule presented in Principle 2 and Diagram 1. It states that if the cue ball hits approximately half


Source: Alciatore, David G. - Department of Mechanical Engineering, Colorado State University


Collections: Engineering