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Billiards Digest May, 2009 David Alciatore, PhD ("Dr. Dave") ILLUSTRATED PRINCIPLES

Summary: Billiards Digest May, 2009
David Alciatore, PhD ("Dr. Dave") ILLUSTRATED PRINCIPLES
"Draw Shot Physics - Part II: examples"
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.
This is the second article in a series on draw shot physics. Last month, we looked at some of
the basics and listed a set of conclusions from a thorough physics analysis (TP B.8). This month,
I want to present some detailed results and show some specific examples that illustrate some of
the conclusions. With a straight-on draw shot (with no cut angle), the draw distance is
determined solely by the amount of spin the cue ball (CB) has at contact with the object ball (OB).
It is important to distinguish between how much spin the CB has off the tip and how much it has
at OB contact, after some spin is lost due to "drag" on the cloth. Diagram 1 shows how much
spin the cue delivers to the CB for different tip offsets. With a small offset (i.e., close to a center-
ball hit), the CB will have very little spin (point "A"). Obviously, as you increase tip offset, the
amount of spin increases. At point "B" (at about 30% tip offset), you get about 50% of maximum
spin; and at point "C" (50% offset), you get about 75% of maximum spin. Maximum spin occurs


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


Collections: Engineering