Summary: Billiards Digest March, 2012
"Ball Weight and Size Difference Effects Part II" ILLUSTRATED PRINCIPLES
David Alciatore, PhD ("Dr. Dave")
Supporting narrated video (NV) demonstrations, high-speed video (HSV) clips, 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 articles 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:
Last month, we looked at ball and weight difference effects. The focus was on square-hit stun, follow,
and draw shots. This month, we'll look at how weight differences affect cut shots and the 90° and 30° rules.
All of the effects are described and demonstrated in online video HSV B.49, which I recently filmed with fellow
columnist Bob Jewett.
Remember, the CB is sometimes heavier on some older coin-operated "bar boxes." Also, even with an
originally equal-weight set, the cue ball (CB) will sometimes be lighter because it takes more abuse from the
cue tip, other balls, and cloth, and wears faster as a result. And if a new CB is used with an older object ball
(OB) set, the CB will generally be slightly larger and heavier than the worn OBs not replaced.
Diagram 1 illustrates the effects of ball weight differences on a stun shot, where the CB has no top of
bottom spin at impact with the OB. With a cut angle, a stun shot sends the CB straight down the tangent line,
which is perpendicular to the line of travel of the OB. This is the famous the 90° rule, which applies only for
balls of equal weight. As shown in HSV B.49, the CB heads straight down the tangent line regardless of stun