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David Alciatore ("Dr. Dave") ILLUSTRATED PRINCIPLES "90 and 30 Rule Review"

Summary: David Alciatore ("Dr. Dave") ILLUSTRATED PRINCIPLES
"90 and 30 Rule Review"
Note: Supporting narrated video (NV) demonstrations, high-speed video (HSV) clips, and
technical proofs (TP), and all of my past articles, can be accessed and viewed online at
billiards.colostate.edu. The reference numbers used in the article help you locate the
resources on the website. If you have a slow or inconvenient Internet connection, you
might want to view the resources from a CD-ROM or DVD. Details can be found online
at: dr-dave-billiards.com.
Periodically, I will write an article presenting a concise summary of principles from past
articles. I think it is useful to review and reflect occasionally to help keep things in perspective
and to reinforce important information. I'm a teacher in my other life and I know how important
repetition and reinforcement are to learning. This article summarizes my previous six articles
dealing with the 90 and 30 rules. Hopefully, by seeing all of the results in one place, knowing
when and how to apply each rule will become clearer.
In my January, 2004 article, I introduced the 90 rule. It states that when the cue ball strikes
an object ball with no topspin or bottom spin, the two balls will separate at 90, regardless of the
cut angle. The cue ball leaves along the tangent line, which is perpendicular to the impact line
(see Diagram 1). Principle 1 and NV 3.4 summarize and illustrate the important points of the
rule. The 90 rule is very useful for helping to prevent scratches (see my January, 2004 article),
plan break-up and avoidance shots (see my February, 2004 article), plan carom shots (see my


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


Collections: Engineering