A billiard ball in motion possesses (movement across the table) and often angular momentum (rotation or spin).
Mastering the physics of pocket billiards isn't about doing calculus in your head during a match; it’s about building an intuitive "physics engine" in your mind. By understanding how momentum, friction, and geometry interact, you stop guessing and start calculating. AI responses may include mistakes. Learn more
In a frictionless environment without spin, the cue ball will travel along a line 90 degrees (perpendicular) to the object ball’s path. This is known as the "90-degree rule." Understanding this tangent line is the secret to master-level position play. 2. Linear and Angular Momentum
On a real table, the cloth exerts friction. A ball that is struck in the center will eventually stop sliding and start "natural rolling." In a natural roll, the ball rotates exactly enough to match its forward speed, creating a predictable path. 3. The Power of "English" (Spin)
Striking the ball above center causes it to rotate forward faster than its travel speed. After hitting the object ball, this "over-spin" overcomes the 90-degree rule and pulls the cue ball forward.
Striking below center creates backward rotation. Upon impact, the friction of the cloth "grabs" the backspinning ball, pulling it back toward the shooter.
When a sliding cue ball hits an object ball full-center, it transfers all its linear momentum to the object ball. The cue ball stops dead, and the object ball moves forward at the cue ball’s original speed.
Below is an exploration of the core physical concepts that govern every shot on the table. 1. The Geometry of the Collision
When you hit the ball with sidespin, the cue ball actually displaces slightly in the opposite direction of the strike.