Shortly after first picking up a cuestick you learned about tangent lines. The reliable law that colliding spheres will always separate along a line perpendicular to the axis of their centers (the middle line in our diagram) has long been a staple of the game.
In our diagram the 8-ball and 9-ball are frozen. Everyone knows that the 8-ball will, when struck by the cueball, move away from the 9-ball along that line. Well, thats great if that line happens to line up with a pocket. But what if it is just ahead of or behind a pocket. Is there anything you can do to send the 8 ahead of or behind that line?
Sure there is. You can use the gear effect to either apply topspin or draw to the 8-ball and alter its path as we have shown in the diagram. How much you can alter it depends on the distance from the closest rail or pocket and how well you stroke the shot.
The gear effect tells us if we stroke the cueball with draw that we will impart follow to the 8-ball and that if we stroke the cueball with follow then draw will be imparted to the 8-ball. But knowing this by itself is of little value. What is vital is to know how far you can alter the straight tangent line path.
So you must set the balls up as shown on whatever table you play upon and try it out to determine how far you can bend the 8-ball. First, place the balls at center table so that the tangent line intersects the side pocket. Shoot the shot with center and watch the 8 drop in the side. Now set the shot up the same way but shoot it with extreme draw.
The 8-ball will now miss the side pocket and strike the rail as much as half a diamond away from the pocket. You have imparted follow to the 8. Imparting draw is much tougher. But try it. Set the balls up and shoot the shot with extreme topspin. The 8 will now alter its path back towards you.
What you probably noticed is that the 8-ball did not vary from the tangent line as much this time. That is because it is more difficult to impart draw than follow. But practice the shot and know how much you can alter the path of the 8. Even a quarter of a ball width can mean the difference between missing and making many shots.
