Why is a 1/2-ball hit (30° cut angle) so useful?

Here’s an excellent videos Mike Page put together on half-ball hit “gems:”

NV B.6 – Mike Page’s half-ball hit gems (part 1, part 2)

and here’s a good summary article from Bob Jewett (BD, November, 2000). The “natural angle” effect associated with a half-ball hit is one of the most important principles in pool and billiards.

Gem #4 from the video is the basis of the 30° rule, which states that for a rolling CB, the carom angle is very close to 30° for all cut angles between 1/4-ball and 3/4-ball hits (not just a 1/2-ball hit). This gem is the single most important and useful principle in pool, especially when used in conjunction with the peace-sign technique:

Gem #4 is an interesting proposition demonstration with the carom shot from the foot rail. NV A.1 shows a similar “sure-thing” proposition. The following article also illustrates and discusses the shot in “The 30° rule: Part III – carom vs. cut” (BD, June, 2004).

TP A.1 and TP A.2 present an error analysis and look at the effects of table size.

Gem #2 is explained and illustrated in detail in “Draw Shot Primer – Part I: physics” (BD, January, 2006). The concept can also extended into the trisect draw-shot aiming system. This is also a very useful “gem.”

Many additional resources, with lots of illustrations, examples, and video links related to these principle, can be found here:

Math and physics backing up Gem #’s 2, 3, and 4 can be found in TP 3.3, TP A.4, and TP A.16.

The 1/2-ball hit is a common shot, especially in the game of 9-ball, where you need to move the CB around the table a lot. With a 1/2-ball hit, the CB easily be given enough speed to travel significant distance. The CB’s motion can also be killed fairly easily with a 1/2-ball hit. Also, sidespin is very effective off the cushions with a 1/2-ball hit. For thinner hits, the faster ball speed reduces the effect of the sidespin; and for fuller hits and the resulting slower speed of the CB, the spin doesn’t grab as well, especially on new cloth.


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