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Billiards Digest October, 2011 "The Lag Shot" ILLUSTRATED PRINCIPLES

Summary: Billiards Digest October, 2011
David Alciatore, PhD ("Dr. Dave")
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 my articles will 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.
The topic for this article is the lag shot, which is used to determine who breaks first. Lag shots aren't
typically used in league play; but they are often used in tournaments. The winner of the lag has a big
advantage in being awarded the first break, especially in a winner-breaks event. Even in alternating-break
format, the lag shot can be the determining factor of the match if it goes hill-hill and the winner of the lag gets
to break for the deciding game.
Last month, we looked at recommended tip contact-point heights for different situations and indicated that
the optimal height for consistent speed/distance control is 0.2R, as illustrated in Diagram 1. This is the best
tip height to target when shooting a lag shot. Diagram 2 shows why. The graph, which is from the math and
physics analysis in TP B.12, shows how cue ball (CB) travel distance varies with tip height, for a given cue
speed. With a center-ball hit (point "A"), the cue moves the CB forward initially with the most speed, but the
CB slows as it slides (drags) across the cloth and develops forward roll. With a maximum above-center hit
(point "C"), at the miscue limit (0.5R), the CB doesn't require drag to develop roll, but the forward speed of the


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


Collections: Engineering