David Alciatore, PhD ("Dr. Dave") ILLUSTRATED PRINCIPLES "90 and 30 Rule Follow-up Part II: speed effects" Summary: David Alciatore, PhD ("Dr. Dave") ILLUSTRATED PRINCIPLES "90° and 30° Rule Follow-up ­ Part II: speed effects" 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 3.4) help you locate the resources on the website. You might also want to view the resources from a CD-ROM. See the website for more details. In last month's article, I answered a few basic questions that have come up concerning my series of articles on the 90° and 30° rules (see my January through June, 2004 articles at billiards.colostate.edu). In the next few articles, I'll look at the important effects of English, speed, and other factors on the 90° and 30° rules. If you don't remember what the 90° and 30° rules are and when they apply, see NV 3.4-3.5 and NV 3.7-3.10. Readers with engineering or physics backgrounds might also find TP 3.1 and 3.3 interesting. Remember, the 90° rule states that for a stun shot, where the cue ball is sliding at object ball impact, the cue ball and object ball paths separate at 90° (i.e., the separating paths are perpendicular). The 30° rule states that when the cue ball is rolling at object ball impact, and when the cut angle is between a 1/4-ball and 3/4-ball hit fraction, the cue ball's path will be deflected by approximately 30°. If these previous two sentences are not clear, you might want to look at the online videos and articles mentioned above. normal video NV 3.4 ­ 90° rule with various cut angles Collections: Engineering