Swerve

• contributing factors
• OB "swerve" and "turn"
• reducing swerve
• squerve

for more information, see Section 4.04 in The Illustrated Principles of Pool and Billiards
and Disc II of the Video Encyclopedia of Pool Shots

contributing factors

What factors affect how much the cue ball swerves?

See my March '08 instructional article. It summarizes and illustrates all of the important factors and effects. A complete summary of all squirt, swerve, and throw effects can be found here. See also: squirt, swerve, and throw confusion.

OB "swerve" and "turn"

Can an object ball swerve or turn due to sidespin?

First of all, OB "swerve" or "turn" should not be confused with throw, which is an entirely different effect.

Here are some videos that demonstrate the lack of significant turn:

NV B.7 - Ball "turn" caused by sidespin

NV B.8 - Straight throw of a second object ball

A slight amount of "OB swerve" is possible with masse spin transferred to the OB from follow or draw on the CB (see the end of TP A.24), but the effect is much too small to be of practical importance. With the videos above, I am just looking at the effect of pure sidespin as a ball is rolling. I call this effect "OB turn."

TP B.2 provides a physics and math-based approach to the question of whether or not a ball rolling with sidespin can turn. Here are my conclusions: A ball rolling with sidespin goes straight for all practical purposes, and cloth irregularities can create a much bigger effect, especially at slow speeds. Sometimes the ball will go straight as it slows with right spin, sometimes it will curve right as it slows with right spin, and sometimes it will curve left as it slows with right spin. Having said that, the physics does seem to suggest that there might be a small tendency for the ball to curve in the spin direction (e.g., right curve for right spin), but due to the assumptions in the analysis and the results of the video demonstrations, the value of this information is questionable.

from Jal:

A ball with a masse spin component will change direction by the same amount regardless of how slick or "grabby" the cloth. But a more grabby cloth will cause that change of direction to happen sooner, so the curve will be tighter. In your example, a slicker cloth might be of some help since you want the 1-ball to execute a more open curve in order to clear the 2-ball.

However, an OB will not curve to any significant extent without being struck by an airborne cueball. That is, in order to induce a masse spin component, the cueball has to contact it above the horizontal equator. ... this will also cause it to jump. The combination of jump and subsequent curve might be enough to clear the 2-ball and then "straighten out" after landing/bouncing and head for the pocket.

In principle, you can get the OB to curve just be using draw or follow at any non-zero cut angle. But calculations indicate that, at most, the change in direction is miniscule (in fact, very hard to measure and probably overridden by random buffeting by the cloth's weave pattern).

dr_dave reply to Jal:

I agree 100%. OB swerve is not a significant-enough effect to be of any practical use. The effect is larger in clingy conditions, but still not significant enough to be useful or even noticeable, IMO.

IMO, the best chance to seemingly make an OB curve around an obstacle is by jumping the CB into the OB, creating OB hop over the obstacle ball, or by relying on table roll-off, a lopsided (non-round OB), or well-placed dirt or irregularities on the cloth. The rail groove can also influence an OB close to the cushion. Even the magical cue twist and swoop technique won't work (without a weighted ball).

from Bob Jewett:

Here is [an experiment you can use] to test your bending technique:

reducing swerve

Can swerve be eliminated with an above-center hit?

The closer the cue is to level, the less a shot with English will swerve. Unfortunately, because of the height of the rails, the diameter of the cue (above the rail), and clearance between the cue and rail, the cue will not be level on most pool shots. Also, if you hit above center with English, the squirt direction is down a little; so even with a level cue, an above-center hit still results in slight swerve action (because the effective impact direction is still down a little).

Having said all of this, an above center hit can reduce cue elevation and reduce the effects of shot speed and ball/cloth conditions (i.e., there will be less swerve).

squerve

What is squerve?

Squerve, sometimes called "effective squirt," is the combination of squirt and swerve. For more information, see my March '08 and April '08 BD articles. For a summary of all of the factors affecting squerve, see: squirt, swerve, and throw effects. Also, here's a video excerpt from Disc II of the Video Encyclopedia of Pool Shots that explains and demonstrates things: