Understanding bowling ball motion will help you make a good decision in purchasing your next bowling ball. This article is addressed to the advanced and highly skilled bowlers but has relevant information for everyone interested in the science of bowling ball motion. Understanding Bowling ball motion is simply derived by examining the overall path a bowling ball takes while traveling down the lane derived from research and development by manufacturers and amplified by field studies performed by the United State Bowling Congress (USBC).
The USBC, combined with the ball manufacturers, did graphical analysis using the Computer Aided Tracking System (CATS) to accurately measure the resulting ball motion when a drilled ball was thrown by an automatic ball throwing machine to simulate a bowler delivering a bowling ball on a lane with a 53 foot flat oil pattern. That graphical analysis showed the three phases of ball motion for each ball tested.
When a bowler delivers a ball, the bowler imparts four forces to the ball:
1. initial ball speed
2. initial rev rate
3. initial ball axis tilt
4. initial axis rotation
These factors, plus the location of the Positive Axis Point, describe a bowler’s delivery during ball motion testing. As the ball travels down the lane, it passes through three phases and two transitions. This motion happens as follows:
1. the skid phase (the first transition from skid to hook)
2. the hook phase (the second transition from hook to roll)
3. the roll phase
During the skid phase, the force from the ball speed exceeds the force from the rev rate. As the ball travels down the lane, the friction between the ball and the lane reduces the ball’s speed and increases the ball’s rev rate. When the forces from the ball speed and the rev rate become equal, the ball transitions (first transition) into the hook phase.
In the hook phase, the force from the ball’s rev rate exceeds the force from the ball’s speed. During the skid and hook phases, the ball’s axis rotation always exceeds the ball’s axis tilt. The ball will lose its’ axis rotation faster than it loses its’ axis tilt during the skid and hook phases.
When the ball’s axis rotation and axis tilt become equal, the ball will transition (second transition) into the roll phase. Once the ball enters the roll phase the ball will no longer hook and the ball’s axis rotation will always equal the ball’s axis tilt. The axis rotation and axis tilt will decrease slowly as the ball travels down the lane during the roll phase. The bowling ball will reach its’ maximum rev rate at the second transition. The ball’s rev rate will always be less in the skid and hook phases than it is in the roll phase.
The bowling ball always hits harder after it stops hooking (the roll phase), rather than while it’s still hooking (the hook phase). Once the ball reaches its’ entry angle at the second transition, the entry angle will remain the same until the ball hits the pins. This is a scientifically accurate description of bowling ball motion.
There’s one more fact that must be mentioned which affects the shape of the drilled ball’s motion, and we are only concerned with drilled bowling balls. It has been proven that all drilled bowling balls are asymmetrical, whether they are symmetrical or asymmetrical before drilling. To be considered asymmetrical, a bowling ball must have a measurable intermediate differential and a Preferred Spin Axis (PSA). And, all drilled bowling balls have both those measurable properties.
All this information was verified during the Ball Motion Study, which was conducted by the Ball Motion Task Force. The Ball Motion Task Force consisted of the USBC Equipment and Specifications Department and the ball manufacturers.
A key to ball motion is intermediate differential which is the measure of a bowling ball’s degree of asymmetry. Differential ratio is simply defined as the intermediate differential divided by the total differential. Differential ratio is expressed as a decimal valuation. The larger the differential ratio, the more asymmetrical the bowling ball. Conversely, the smaller the differential ratio, the less asymmetrical the ball.
According to the Ball Motion Study, ball motion is affected by:
1. coverstock - The study proved that the most important factor in determining ball motion is the ball’s coverstock.
2. mass properties (ball dynamics)
3. static weight balance.
Next in importance is the mass properties of the ball provided by the core density and core shape. The net effect is that the coverstock aggressiveness (chemistry plus surface texture), RG (Radius of Gyrations) and total differential have similar effects on a drilled ball’s motion. These factors affect the location of the first transition on the lane and they determine how soon a ball starts up on a given lane condition.
After choosing a given bowling ball with the given coverstock, the static weight balance dynamic shifts in accordance with the drilling layout pattern, final factor important in achieving the desired reaction. The drilling technique consists of the layout and the balance hole location and size (if a balance hole is desired).
Symmetrical balls yield drilled balls with smaller differential ratios. Small differential ratios will produce a drilled ball with a smoother, more controllable motion when compare to an undrilled asymmetrical ball.
Varying degrees of longer transitioning (longer h
ook zone) ball motion can be obtained by choosing to drill an asymmetrical ball. Asymmetrical balls after drilling show a defined, angular motion. These balls can create more area at the break point and will respond to friction faster at the break point than symmetrical balls.
We hope this scientific approach to sharing information helps you in understanding bowling ball motion. We recommend you consult your local pro shop professional when selecting a new bowling ball and a drilling layout to obtain the targeted ball motion you seek.
