Let's say you have become a pretty good shot maker. You can sink an object ball from just about any position on the table&endash; within reason. What's next?
Most players would say "learning position" is the next step, but that answer is too all encompassing to be very helpful. Playing position, in the broad sense, involves a large number of cue ball dynamics beyond just speed. Trying to learn them all simultaneously can be daunting. So, in order to learn to play position by the numbers, let's start with the most important factor, which is speed. If you can surgically control the cue ball's speed with each shot, it may never be necessary for you to know much more. Master the cue ball's speed, and you are a master of the game.
If the cue ball never has to contact a rail in order to get position for each successive shot, your chances of running out are greatly improved. Now, repeat that last sentence three times. Never forget it, because ideally, the most desired placement for the next position shot is one that will not require contact with the rail for the next shot in the sequence. Although many advanced players prefer going to a rail for position, in theory anytime the cue ball must hit a rail for position, the odds of achieving it are reduced. Why?
The fewer concerns we have to deal with on a shot, the more focus and attention we can give the remaining considerations. For example, if speed is the only thing we have to worry about to get position, the goal will be more easily achieved than if we have to calculate both speed and rebound dynamics off a rail. With good speed control, it will be easier to get a leave for the second ball, that in turn will make it possible to get shape for the third, without going to a rail. This also relates to the reasoning behind planning no more than three balls ahead. But, even if you must use the rails ( and we all do) speed is still the critical factor.
The lag is often used to determine who has the break before a game. Both competitors place their cue balls behind the head string and simultaneously drive them to the foot rail so that they rebound back exactly one table length to the head rail. The shooter ending up nearest the head rail breaks. The lag is the most obvious test of your speed control. How often do you end up against the head rail after the lag? How often do you practice the lag? It should be part of every practice session, because "lag speed" also happens to be an important and routine stroke for many other shots. Consider lag speed as a constant around which you build your speed control.
Obviously there is a big difference between controlling speed to the object ball, and knowing what the speed will be after contact. Whenever the cue ball hits another ball or the rail, the speed is reduced by a predictable amount (running english not considered here). I use a simple formula to help determine how fast the cue ball will leave the object ball after contact. I have never seen it used or referred to anywhere else, but it is a system I use to help others understand the physics involved.
If the cue ball hits the object ball full in the face with no top or bottom english, it will stop dead in its tracks as the object ball takes off at the same speed the cue ball was traveling when it made contact (a small fraction of the energy is lost in the exchange, but not enough to matter.) 100% of the cue ball's energy (or momentum) is surrendered to the object ball.
If the cue ball makes a 3/4 hit on the object ball, it will surrender 75% (3/4) of its energy to the object ball, and retain only 25% of its contact speed. The object ball's deflection speed will be 75% of the cue ball's contact speed. (A 3/4 ball hit is when the inside edge of the cue ball intersects with a line drawn "3/4" of the distance from the outside edge of the object ball. The balls below are shaded to represent these intersecting points.)
3/4 Ball Hit
If the cue ball makes a half-ball hit on the object ball it will surrender half of its energy to the object ball, retain half of its energy, and both balls will travel at half the speed the cue ball was traveling before contact. Now the point should be getting obvious. (Note that both balls below are shaded "1/2" distance in from their edges.
1/2 Ball Hit
A common mistake in speed control relates to this formula. Too often the shooter will attempt a very thin hit&endash; let's say a 1/10 ball hit&endash; and fail to realize that the cue ball will retain 90% of its speed after contact, and they over-shoot their position dramatically.
1/10 Ball Hit
It might be obvious now that whenever the cue ball and object ball make contact, the deflection speeds of both must add up to 100%, each with a share of the speed (or energy) determined by the fullness of the hit. Remember: In order for the total combined deflection speeds (cue and object ball) to exceed the cue balls speed at contact, another factor must influence the hit. And it does. Spin (side, top and bottom) is another form of energy, and does enter the picture. But that will be discussed at the end of the session.
Speed relates to distance. With a 3/4 hit, not only will the cue ball deflect at 25%, and the object ball at 75% of the contact speed, the object ball will travel 3 feet for every 1 foot traveled by the cue ball.
In the diagram below the cue ball was stroked with a speed that would send it 4 feet. When it hits the object ball (a 3/4 hit) the object ball is sent 3 feet, and the cue ball 1 foot. The distance is equal to the percentage ratio (3 /1 ft. = 75/25%.)
You can test this for yourself. Put an object ball on the head spot. Place the cue ball between the object ball and the head rail so that the inside edge of the cue ball is lined up as shown below. The inside edge of the cue ball is lined up to intersect a point 3/4 the distance from the outside edge of the object ball (25% from the inside edge.) If this is confusing, just set up as shown below.
Stroke the cue softly with a center ball hit. Drive the object ball 3 feet, and then measure the distance the cue ball traveled after the hit. It should be 1 foot.
If you drive the object ball 6 feet with this same set-up, the cue ball should travel 2 feet (6/2=3/1 ratio, or 75/25).
You can test the half-ball (50%) hit the same way. After contact, both balls should travel at equal speeds and the for same distance. But what about extremely thin hits? Well, lets try one at lag speed&endash; the speed that we use to determine who breaks.
First, practice your lag shot until you can leave the cue ball fairly close to the head rail consistently. This is your drill speed.
Now, set up the table as shown below and pocket the object ball with a lag speed stroke. If you pocketed the ball with a 1/10 ball hit, the cue ball will retain 90% of its contact speed and travel about 90% of the distance to the head rail.
Invent your own speed drills and practice them until your speed becomes instinctive. If you start thinking about all of the speed and spin dynamics during a match, you will probably get "brain clutter" and choke. This is why practice time is so critical. Remember: "When it's time to perform, the time to practice has passed."
I stated earlier that other ball dynamics can effect deflection speed, which in turn effects distance and tangents. Top and bottom spin are the main considerations. Top spin can dramatically change the behavior of the cue ball after contact with the object ball. It will cause the cue ball to travel a greater distance, while affecting the object ball's speed and distance very little, if any at all. Bottom spin can slow the cue ball (with cloth friction), with little or no affect on the object ball's speed.
Side spin can change speed and deflection dynamics to a small degree. But the value of side spin is only apparent when rail shots come into play.
Billiard World 1998 Edition
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