Dr. Dave's answers to frequently-asked questions (FAQs), mostly from the AZB discussion forum

for more information,
see Sections 3.03 and 5.02 in The
Illustrated Principles of Pool and Billiards

and Disc I of the Video Encyclopedia of Pool Shots

**ball
speeds and travel distances**

*How
do cue ball and object ball speeds and travel distances vary with cut angle?*

For stun shots, see the graph and summary statements on page 2 of:

For roll shots, see the graph and summary statements on page 3 of:

TP A.16 - Final ball speeds, distances, and directions for natural roll shots

and see:

TP B.5 - Rolling CB, direct-hit hop and ball travel distances

Here are some useful conclusion statements from the analyses:

- With a stun shot, the cue ball and object ball speeds and travel distances are the same for a 45-degree cut angle. The post-impact speeds are equal and about 70% of the initial cue ball speed. The distances are also equal and 50% of the distance the stunned cue ball would travel if there were no collision.
- With a rolling cue ball,
the ball speeds and distances traveled are the same at a little less than a 1/2-ball
hit,

which is slightly more than a 30-degree cut angle. - If a rolling cue ball hits an object ball squarely, the object ball will travel about 7 to 8 times farther than the cue ball after impact. This number can vary quite a bit with ball and cloth conditions.
- Distance vs. cut angle and ball-hit fraction plots, and approximate ball-distance proportions for various common angles can be found on pages 10 and 11 of TP A.16.

"Fundamentals - Part VII: speed control" (BD, March, 2009) also provides some good illustrations and examples.

*What is tip height on the cue ball results in the best speed and distance consistency?*

See optimal tip height for speed control.

*Where can I find general advice and drills for improving speed control?*

See "Fundamentals - Part VII: speed control" (BD, March, 2009).

Target practice drills are also very helpful for developing CB speed and position control.

The following stun shot drill is also helpful for improving speed control: NV D.8 - Stun Shot Drill - from Vol-II of the Billiard University instructional DVD series.

**optimal tip height for speed control**

*Where is the best height to hit the cue ball for speed and distance control and consistency?*

To help achieve the best speed and distance consistency, it is best to hit the CB at about 20% of the radius above the center (0.2R), which is about 60% of the total ball height (see "d" in the illustration below). For illustrations and explanations, see "The Lag Shot" (BD, October, 2011) and "How High or Low Should You Hit the Cue Ball?" (BD, September, 2011). Hitting above center can also result in a more accuracy with CB direction (see follow accuracy).

*How much speed does the CB lose when it rebounds off a rail cushion?*

For steep angles into a rail, where the CB path is close to perpendicular to the rail (i.e., almost straight into the rail), the CB loses about half of its speed after rebound and skid. For more information and demonstrations, see:

HSV B.15 - straight-on kick shot rebound losses and spin changes for roll, stun, and draw shots

At very shallow angles to the rail, where the CB is moving almost parallel to the rail, very little speed is lost off the rebound.

**typical speeds for a range of shots **

*How fast does the CB travel for a range of shots?*

Here are some typical values for various shot "speeds" in miles per hour (mph), feet per second (fps), inches per second (ips), centimeters per second (cm/s) and meters per second (m/s):

soft touch: <1 mph = <1.5 fps = < 18 ips = < 45 cm/s

slow: 1-2 mph = 1.5-2.9 fps = 18-35 ips = 45-89 cm/s

medium: 2-4 mph = 2.9-5.9 fps = 0.89-1.9 m/s

fast: 4-7 mph = 5.9-10.3 fps = 1.9-3.2 m/s

power shot: 7-10 mph = 10.3-14.7 fps = 3.2-4.5 m/s

powerful break: 25-30 mph = 37-44 fps = 11-13 m/s

ridiculously powerful break: 35 mph = 51 fps = 16 m/s

One way to characterize different shot speeds is in terms of "table lengths of travel." Refer to TP B.6 - Cue ball table lengths of travel for different speeds, accounting for rail rebound and drag losses to see how shot speed and "table lengths of travel" are related.