Two Balls, Two Pockets: The 90-Degree Carom

Trick shot #5 of 15Difficulty: ★★☆Teaches: The 90-degree rule and where the cue ball goes after a cut

Cut one ball into a corner and send the cue ball off at 90 degrees to knock a second ball into the other corner. Pure geometry, and very useful to know.

White dashes: cue ball path. Yellow dashes: object ball path.

Setup

1. Place the first ball about one and a half diamonds out from a corner, and the cue ball for a cut of 40 to 50 degrees.
2. Place the second ball on the line 90 degrees from the first ball's path, aimed at the opposite corner.

How to shoot it

1. Hit the cue ball dead center (or a touch below) with firm speed so it slides, not rolls, into the first ball. That is called a stun shot.
2. After contact the cue ball leaves along the "tangent line," 90 degrees from the first ball's path, and caroms the second ball in.

Why it works

When a sliding cue ball hits an object ball, the two balls always separate at 90 degrees. Topspin bends the cue ball forward of that line and draw bends it back, so center ball gives the clean 90.

Common mistakes

• Hitting with follow at soft speed. The cue ball rolls and curves forward, missing the second ball.
• Setting the second ball by eye. Lay a cue along the tangent line to place it.

In a real game

The 90-degree rule is how good players see where the cue ball goes, and how they avoid scratches. Learn it with this shot and you'll use it every game.