Throw
Many people are familiar with the ghost ball aiming technique where you place an imaginary ball against the target object ball and in line with the desired pocket. The imaginary, or ghost, ball becomes the point of aim for the cue ball in order to pocket the object ball. While this works well in most cases, this technique begins to break down when balls are close to or frozen to each other, which is often the case for trick shots involving clusters of balls. I'm going to explain why the ghost ball technique breaks down and give you some pointers on how you can adjust for it.
When two balls are frozen to each other (touching), there will be frictional forces between them when one of the balls begins to move. This frictional force pushes the second ball a little bit off its original line of aim (see the red ball in the diagram). This is called "throw." The reason throw is more apparent when the balls are frozen has to do with the coefficients of friction. There are two coefficients, static and dynamic, and the static one is greater. You can rationalize this by imagining trying to move a large piece of furniture; you exert more effort to start it moving and less effort to keep it moving. Likewise, when the balls are frozen together, the coefficient of static friction will offer a greater contribution to the frictional force than when one ball is already moving.
Here is an exercise to help you understand throw a little better. Place a ball on the head spot (the 9 ball in the diagram). If you want it to go straight down the centerline of the table, you would imagine the ghost ball to be directly behind it. Now, instead of imagining the ghost ball, put an object ball directly behind it aimed down the centerline of the table (the 1 ball). If you place the cue ball directly behind these balls and hit into the combination (dotted cue ball), the 9 ball will go directly as intended, straight down the center of the table. Now, move the cue ball a half diamond the right (cue ball A) and again, hit straight in to the combination. The first object ball now throws a little bit to the left (blue line) instead of going straight down the table. Repeat this using different cue ball positions and see how far away from the center of the table the first object ball throws and if there is a maximum. Another test to try is to keep using the same cue ball position, but change your speed. You will find that the 9 ball throws more with slower speed.
So, what does this have to do with trick shots? For setup shots, balls are generally frozen together. The direction that some of these frozen balls will travel depends on how they are aligned. The three ball cluster by the side pocket set up with cue ball A is seen in shots like Just Showing Off. The 9 and 10 balls are aligned straight out from the side pocket and the 11 ball is aimed toward the corner pocket. However, since the cue ball is approaching from the right side of the 10-11 line, the 11 ball will throw a little bit to the left. To compensate for this, the 11 ball should be aimed towards the long rail point of the corner pocket. In the above exercise, the 9 ball threw over 3/4 length of the table. In this shot, the 11 ball only goes about 1/2 the length of the table, so not as much adjustment is needed. Again, you can try this shot at different speeds and see exactly where you need to aim the 11 ball. The shot on the headspot for cue ball B is another common component to a setup shot (see Kyoto Freeway). Here, there is even less distance for the 12 ball to throw, so not as much adjustment is needed. You can aim the 12-13 ball combination to the right half of the 12 ball's corner pocket and that will give you plenty of room.
Throw is an important concept to understand and can be the difference to a made or missed shot. Being armed with this information, and knowing what kind of adjustments you can make to compensate for this effect, will help you become a more successful trick shot artist and pool player.
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