The truth about axis migration and core dynamics

By Nick Siefers, USBC Research Engineer

Many theories about why and how a bowling ball rolls down a lane have been discussion topics within the bowling industry in recent years, including at the United States Bowling Congress, where a ball motion study is a major research focus.

With key trends appearing in the data, the significant factors that affect bowling ball motion are becoming scientifically apparent. A separate study relating to how and why the ball rolls the way it does has been conducted. In the following discussion, an attempt will be made to explain the physics that govern bowling ball motion relating to core dynamics.

Of the many theories available to explain the motion of a bowling ball, different companies take a wide variety of stances on this subject. Several beliefs include the following:

1. Core dominates cover
2. Cover dominates core
3. Core and cover have a delicate balance with each other
4. Mass bias strength governs axis migration
5. Asymmetrical vs. symmetrical cores determine bowling ball motion
6. RG, differential and cover stock work together to affect the roll
7. Other(s)

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USBC Center of Gravity preliminary test

By Paul Ridenour, USBC research engineer
A hot topic on Internet forums recently has been the effect of center of gravity placement in symmetrical bowling balls. The two main pieces of evidence for this study are videos by Brunswick regional Professional Bowlers Association staffer Nick Smith, whose video can be found at brunsnick.com and Lane #1 president Richie Sposato, whose video is at lane1bowling.com.

Those videos are effective visual evidence. For a more in depth look, the USBC research staff decided to use robotic ball thrower Harry to roll the balls.

This article will discuss the theory behind center of gravity effect on ball motion and will give preliminary conclusions observed from C.A.T.S. data.

When bowling ball companies design bowling balls in CAD programs, they usually have a certain pin to center of gravity distance in mind. Because of variation in the manufacturer’s process, USBC receives pin out distances that vary from 1 inch to sometimes 6 inches. When bowling balls are marketed, the figures for total differential and radius of gyration are completed from the model of that particular ball on a CAD program. According the some ball manufacturers, the statistical numbers of a bowling ball can vary from the CAD numbers by about plus or minus 3 percent. The only way to truly measure those numbers once a ball is made is to use a radius of gyration swing such as the one USBC has to test bowling balls. [Read more]