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The Physics of Pool and Billiards

Draw: Draw is achieved by hitting the cue ball below its center. First the ball rotates in backward motion. This rotation slows as the pool ball slides, and then the ball rolls forward like it does on other shots. The harder you shoot, the farther the ball will travel while maintaining its backward spin. And the lower you hit the ball, the farther the ball will travel with this backward spin. If the cue ball hits another pool ball solidly, when it still is spinning backwards, the backward spin will make it come back toward you, after its collision. This is considered the classic draw effect.

Follow: The opposite of draw is follow. This is done by hitting the cue ball above its center. The cue ball then rotates forward. If the cue ball then hits another pool ball, it will roll forward after its collision. But the cue ball has a natural follow, just because of it rolls on the cloth, so you can achieve the follow effect with center ball if you allow the cue ball to start rolling before it strikes another pool ball. When the cue ball that has follow or draw strikes another pool ball solidly, it will stop for an instant (still spinning) before the follow or draw happens.

Center ball: When you hit center of the pool ball, the cue ball slides for a ways, and then rolls. Actually, the ball begins to roll immediately, but the slide predominates over the roll, at first. The harder that you hit the ball, the farther that it slides before the ball starts rolling.

Miscue: While playing pool this usually happens when you try to get extreme side English, follow, or draw. This is when the cue bounces off of the side of the cue ball, instead of solidly hitting it. The sound that it makes is the cue vibrating.

Stop shot: The stop shot is one of the most common and useful shots in pool. When the cue ball is really close to the object billiard ball, this can be accomplished with center ball. The cue ball slides to the object ball and stops dead as the object ball shoots ahead because of its collision. However, most stop shots are done with a little draw. You can use just enough draw that the cue ball stops sliding just as it strikes the object ball. This probably sounds difficult to judge. However, it is fairly easy with a little practice. You will soon learn to adjust your speed and amount of draw, depending on the shot.

Aiming: Many pool players aim directly at the "ghost" ball. I guess there are several alternative tricks. Another is to concentrate on the cue ball and hit the exact correct contact point; Most people probably do this. Another is to adjust your aim until the shot feel right subconsciously; I think most professional pool players are able to do this. Another pool shooting trick can be to have several standard hits that you are able to shoot at any time: 1/4 ball hit, 1/2 ball hit, 3/4 ball hit, and maybe variations like 1/8 ball hit, and decide which of these to shoot, and then shoot it. Another is to aim for a 1/2 ball hit (practice, so you'll know at what angle a 1/2 ball hit goes), and then adjust slightly to make it thicker or thinner, whatever is required (however you make that decision). All of these require practice. A 1/2 ball hit, by the way, is the easiest, most accurate cut, as the center of the cue ball goes directly toward the very edge of the object ball, giving you an easy target. It is less prone to error than thin or thick hits. For accurate aiming, it also helps to have a consistent, level stroke.

Paths after a collision: When a cue ball or another pool ball strikes the object ball, the object ball then moves away and along the line between the centers of the two balls. You may imagine this image, when you shoot pool, if it will help you aim the cue ball. With some follow the cue ball will proceed to curve forward, and with some draw the cue ball will curve backward, as shown. People do not always notice the curving effect while playing pool, but it can be dramatic if you watch for it.

Side English: American's just call it English. The British people call it side. I will call it side English to make sure I am understood correctly. It is side spin on the ball. The situation is not as simple as shown here, as the ball also starts rolling, and the various spin axes change, causing a small amount of curve in the path of the pool ball. Side English complicates the game a lot, and makes many difficult shots possible which would not be possible otherwise. The important effect of side English is the angle that the cue ball (and to a lesser extent, other balls) bounces off the rail. The second most important effect of side English is called squirt; the cue ball does not go straight in the direction that the cue is pointing, it squirts off to the side a little. Left English makes the pool ball squirt to the right on the table. The more the side English, the greater the squirt will be. And squirt is what causes you to miss shots, and is the main reason that the professionals tell you not to use side English unless you have a good reason to. The third most important effect of side English is called Throw. There is also accidental side English, caused by a bad stroke. And other balls gain side English, mainly by banking off rails (but also because of throw).

Jump shot: Besides putting extreme spin on the cue ball, greatly elevating the cue can make the cue ball jump. If you shoot your break shot (in 8 ball or 9 ball) with an elevated cue, you probably jump your cue ball off the pool table often. Hit down on the cue ball, with center ball or some draw. Using a shorter jump cue makes this even easier, and makes the jump higher and more dramatic; there is a limit to how short a cue can be to be considered legal. The type and thickness of the cloth may be a factor in how high the pool ball jumps. Beginners often shoot a jump shot by hitting the cue ball very low and then miscuing, which is not legal if done intentionally. A jump shot over another ball is not legal in snooker. It is very difficult to aim a jump shot.

Curve: The curve caused by side English is very small, and quite a few people think that a level stroke cannot make the cue ball curve. The physics of pool is quite clear, however; a level stroke with side English does cause a minimal amount of curve in the path of the cue ball. Elevating the butt of your cue will increase the curve dramatically, and will most likely cause you to miss shots. Even higher elevation of the cue is called a masse (massé) shot, which can produce amazing effects, and also tear the felt.

Ball speed: Pool ball speed has many effects. When two of the balls collide, ball speed changes the angle because it delays the curve in the paths of the pool balls, to maximize the effect of follow or draw, a slow speed could be necessary. Conversely, to get a straighter ball path, a fast speed could be necessary. Also a faster speed makes the ball slide farther before friction causes natural follow to take shape. Throw is more effective at a slow speed. The curve of a masse shot happens sooner at a slower speed, but the spin is more at a faster speed, and so it is particularly difficult to get the speed of a masse shot correct. And ball speed dramatically changes the angles of kicks and banks.

For "squirt," see "side English," above.