Making a bowling ball is more complex than simply making a sphere of solid resin and drilling three finger holes into it. Nested inside a pro bowling ball hides an asymmetrical core. These weights take on a variety of futuristic-looking shapes that, as PopSci explains, “leverage the laws of physics to help skilled alley jockeys throw a strike on most rolls.”

See just one style of these cores in this “how it’s made” video about mass-produced bowling balls in one South Korean factory. The All Process of World YouTube channel documents each more-complex-than-expected step.

“Put simply, RG [radius of gyration] is a measurement of the distance between the ball’s center of mass and the tip of the invisible axis that extends to the ball’s surface. (The technical definition: “The square root of the moment of inertia divided by the mass of the object.”) The lower a ball’s RG, the more spin a bowler can create by applying torque; the higher the RG, the more power required to rotate the ball. The most common analogy that ball designers use is that of a spinning figure skater, who can slow down their speed by extending their arms away from their center of mass.”

Note all of the robot arms, as well as the laser etching on the ball’s final surface.