(FAQ) How do you use the tangent line?

(About the Author)

Every time you hit an object ball with a cue ball, there is a minor wonder of physics that affects the cue ball, known as the tangent line. What is amazing about this little bit of table billiards activity is that you can use it to predict cue ball behavior.

Here is how it works. Regardless of the speed of the cue ball and the angle that the cue ball and object ball contact, the cue ball will travel away from the object ball and the contact point between them at right angles.

Sound a little too complicated? Let’s use a couple of visual aids. In the example below, you will see a contact between the cue ball and an object ball. See the line going to the right and left of the touching point? That is the tangent line.

TL1

You can see from the line that the object ball will go into the corner pocket. What you also see is that the cue ball will scratch into the other corner pocket – not something you want to allow, unless there are other balls in the way.

So, what can you do? Most important – don’t slam the object ball into the pocket. Use a lower speed. You have two options:

  • Top spin (“follow”), combined with side spin. Use 10:00, 10:30, 11:00, 11:30, 12:00, 12:30, 1:00, 1:30, or 2:00.
  • Bottom spin (“draw”), combined with side spin. Use 4:00, 4:30, 5:00, 5:30, 6:00, 6:30, 7:00, 7:30, or 8:00.

The lower speed allows the cue ball spin to interact with the cloth and force the cue ball away from the dangerous tangent line. Here is how to use that spin to get away from the dangerous tangent. With slower cue ball speeds, the follow options have the best success of missing the corner pocket.

TL2

Tangent thumb technique

This technique will help you calculate the probable path of the cue ball after it contacts the object ball. This can also help determine whether that path can or should be modified with cue ball spin.

TL3TL4

Put your hand over  the object ball. Point the index finger along the line towards the pocket. Point your thumb 90 degrees out. That is the tangent line. You can check it for scratching dangers and possible contact with other balls.

Key factors

  • With slower speeds, the cue ball has sufficient time to interact with the table cloth and deviate from the tangent line, either with draw or with follow.
  • The more speed the cue ball is traveling on the tangent line; the more difficult it is to force any deviation from the tangent line.

Shallow angles

When the angle is very shallow coming into the object ball, it is difficult to change the cue ball path.

TL5

Summary

Keep some reality in your expectations. Don’t assume that you can (without a whole lot of practicing) repeat an amazing table length draw or that precise position after 3 rails that the pros are so good at accomplishing. You know what you can do – don’t exceed your limits.

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