When watching a bowling ball roll down the lane, it is easy to overlook the forces at work within the ball. The ball is round, and the bowler imparts revolutions, axis rotation, axis tilt and ball speed. The round ball undergoes a transition from to skid to hook to forward roll.
However, unless you own a clear ball with a high power core design, it is difficult to imagine the position of the core and its rotational influences on the hook pattern of the ball. Understanding the shape and density of the core will enable you to evaluate a ball and its possible benefits to your game.
Make no mistake about it! There is no substitute for a good shot. But there is also no substitute for a good ball reaction. Even the best in the game do not repeat every shot. Duplicating the exact launch angle, ball speed, rev rate, axis rotation and tilt, and target accuracy is seldom done twice in a row, much less for an entire game. Having the proper ball reaction helps to minimize the consequences of making physical mistakes. Minimizing the mistakes helps build confidence. Building confidence leads to a looser armswing and less intervention of the analytical side of your brain when you are on the approach and on the way to the foul line.
Understanding the ball construction and its application to certain physical styles and lane conditions can be of tremendous benefit to your decision making. The basic component of ball construction is Radius of Gyration (RG). This is a measure of the amount of time that it takes a ball to complete a swing rotation cycle. Without getting into scientific measurements, the more the weight is concentrated toward the center of the ball, the faster the ball will swing. This is called Low RG. Its characteristic is to hook sooner. When the weight is located closer to the surface of the ball, the ball will swing slower. This is called High RG. Its characteristic is to have a more delayed breakpoint. The RG of the ball will dictate its breakpoint.
The second measurement of a ball's dynamic potential is called RG Differential, or Differential for short. The differential is based on the shape of the core. Every core has a height and a width. Picture a softball. Its length and width are identical. No matter which plane you would perform an RG swing on, the swing time would be identical. This would result in no differential. This type of core would have a smooth rolling, low hook potential. Now picture a tall drinking glass. Its height is disproportionate to its width. There is much more mass vertically than horizontally. This ball would have a large difference between the swing rates. This core shape would have a high differential. Differential causes track flare and is an indicator of the speed of transition from skid to hook once the ball encounters lane friction. RG Differential is an indicator of the amount of hook potential at the breakpoint. This drinking glass core would be an example of a high differential, pin-in ball.
The third measurement of a core's dynamic potential is called Mass Bias. To illustrate mass bias, let's use the drinking glass again. But we're going to add a handle on its side, turning it into a mug. Like the drinking glass, there is a difference in the height and width. But there is an additional difference between the width including the handle and the width without the handle. There is more mass closer to the surface in the area of the handle. There is a second differential between the swing time of the handle side and the side perpendicular to the handle. This difference can be minor, as in the case of a pin out ball, or major, as in the case of a ball using BOMB technology. A pin-out ball would have a small handle, a weaker influence. A BOMB core would have a larger handle, a stronger influence. Mass Bias changes the shape of the breakpoint. By shape we mean the amount of time it takes the ball to go into a forward roll. Forward roll occurs when the ball loses axis rotation (side roll). When a ball achieves forward roll, it has ceased hooking and now is rolling in a linear direction. Promoting a quicker forward roll would be beneficial in heavier oil conditions, promoting a slower transition to forward roll would be beneficial in lighter oil conditions.