The Effect of Softball Properties on Batted Ball Distance by Dr. Michael V. Cioccoa and Dr. Mark McDowellb aMichael V. Ciocco, Parsons Project Services, Inc., P.O. Box 618, South Park, PA 15129 bMark McDowell, Bomani Sports Research, Inc., P.O. Box 81402, Cleveland, Ohio  44181

Introduction

In a previous article [1] we discussed the how the properties of a softball effect the batted ball speed. It was shown that a softball’s hardness, measured as compression, was the dominant factor with respect to batted ball speed. The higher the compression the higher the batted ball speed.

But what about distance? As it turns out correlating distance with ball properties is a very complex problem. Because a homerun in softball travels 300-400 feet through the air the aerodynamic properties of the ball become very important. The major aerodynamic properties of softballs that can affect the ball’s flight include; weight, size, seam height, and ball spin.

The weight of a softball can be important because heavier balls are less effected by drag forces (resistance moving through the air) and therefore will travel farther than a lighter ball given the same initial speed, angle, grip, etc.

Size of the softball is important because drag forces are directly proportional to the cross sectional surface area of the ball. Therefore a larger ball will not travel as far as a smaller ball, with all else being equal.

Seam height can be very important with respect to the aerodynamics of a softball. Without going into too much detail the seams create turbulence as the ball moves through the air, and this allows the ball to move through the air easier and therefore farther. The dimples on a golfball, for example, have the same affect. However, it is unclear at what point does increasing the seam height have an adverse effect by effectively increasing the surface area of the ball as well as producing turbulence.

Ball spin, i.e. backspin, has a significant effect on batted ball distance. The more backspin a softball has the farther the ball will travel.

Two measured quantities, compression and coefficient of restitution (COR) currently are used to characterize softballs. Softball compression is a measure of the force (lbs) required to compress the ball 0.25 inches. Softball compression is commonly reported as PQI (lbs/0.25 inch compression). The COR is defined as the ratio of the rebound speed of the ball bouncing off of a rigid wall compared to the ball's incoming speed. That is, if the incoming ball speed is 60 mph and the rebound ball speed is 30 mph the COR = 30/60 = 0.50.

Measuring the actual performance of a ball is more difficult. The most direct and reproducible method of quantifying performance is measuring Batted Ball Speed (BBS) with a radar gun.

In this study three different hitters, with different abilities, swinging two state-of-the-art 30 oz. multi-walled bats with six balls with varying properties from 2 manufactures were used to provide both BBSs and batted ball distances. These measurements were then used to quantify the effect of ball properties on distance.

Experimental

Ball compression testing was performed according to the proposed ASTM Test Method for "Compression-Displacement of Baseballs and Softballs" [2]. All compression testing was performed on an Instron Model 1125 screw-driven load frame. A crosshead speed of 1"/min was used. The load at 0.25" deflection was measured using a fully reversible T/C load cell with a maximum full scale range of 1000 lbs. Deflection was measured directly from crosshead movement and checked manually using a dial gauge. The load was measured at a ball deflection of 0.25" to within +/- 0.002". Testing was performed at 72oF and 45% relative humidity. The balls were conditioned (stored in the test lab) for at least 24 hours prior to testing.

The CORs listed in this study were the stated CORs on the balls. The COR test is an ASTM Test procedure [3] that is intended to standardize a method of measuring the COR of baseballs and softballs. The ASTM COR test is a repeatable and uniform testing procedure based on ball speed measurements before and after impact with either a wood or metal surface. However, the ASTM COR test does not address all safety concerns and states the following: “It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use”. This means that the softball associations are ultimately responsible for controlling the safety of the balls used in the sport of softball.

A Jugs professional pitching machine was used to pitch the balls for the BBS tests. The machine provided consistent pitch speeds (measured via radar gun) in the 16-22 mph range. These tests were conducted indoors in order to provide a controlled and consistent testing environment.

The radar gun used was a Jugs Professional Cordless MPH RADAR GUN (model # R1000). This device is used to measure batted-ball speed and is accurate to within ± 0.5 mph. The gun is used to record the batted-ball speed right after impacting a ball and was placed in the same position for all measurements.

The distance measurements were taken using a Bushnell® Laser Range finder (model #20-0400?, which is accurate to within 3 feet. Only balls with “ideal” trajectories, i.e. those producing the longest hits, were recorded. The average distances for each ball-bat-batter combination were a result of averaging the top 5 distances for each combination.

The bats used were chosen because they are extremely popular Multi-walled 2002 models readily available. Both bats were ASA and USSSA certified. The balls used were chosen to encompass a range of compressions, 375 – 553 PQI, and CORs, 0.40 – 0.47, and were from 2 different manufactures.

Results

Table 1 summarizes the distance results for all three batters, with 6 different balls, using 2 different bats. The average (AVE) for each column is shown at the bottom of the table. In addition the average for each ball is shown in the last 3 columns of the table for all distances and for each bat. Note that all the average distances are over 300’.

Before discussing the different balls a few general conclusions can be drawn from the distance results. Batter 1 hit the ball farther than batter 2 who in turn hit the ball slightly farther than batter 3. Also, for each individual batter and for the average of each bat, Bat 2 hit the ball farther than Bat 1.

As for the individual balls there does not appear to be any correlation between compression or COR with respect to batted ball distance. However, the balls from manufacturer-1 had higher average distances than the balls from manufacturer-2. Plausible reasons for this will be presented later.
 
 

Table 2 summarizes the batted ball speeds (BBSs) for all the batter-bat-ball combinations. Similarly to the distance results player 1 had higher BBSs than player 2 who had higher BBSs than player 3. However unlike distance, the average BBSs for each individual batter and for the average of each bat, the BBSs for bat 1 were higher than for bat 2. This was unexpected because this indicates that higher BBS did not correlate with longer distances from bat to bat.
 
 

With the exception of the 0.47/375 ball, BBS correlates with compression fairly closely. That is, the higher the compression the higher the batted ball speed. This of course is the expected result, the harder the ball the more the bat walls can flex and return energy to the ball. However, as shown from the distance numbers no such correlation exists for distance and compression or COR. Table 3 was developed to help clarify this phenomenon.

In Table 3 the ratio of distance to BBS was calculated and 3 was subtracted from this ratio for each batter-bat-ball condition to help evaluate the results obtained for different batters, bats, and balls, Dist./BBS –3 (D/B ratio).

Interestingly batter 3 had the highest D/B ratio followed by batter 1, both of which were significantly greater than those for batter 2. The most probable reason for the difference was the grips the batters used. Both player 1 and 3 use the Reverse Rotation grip while batter 2 used the overlap grip. The Reverse Rotation grip appears to be performing as its name implies and producing greater backspin than the overlap grip, which in turn increased the D/B ratio.

For each individual batter and for the average of each bat, Bat 2 had a higher D/B ratio than Bat 1. This indicates that there is some fundamental difference between the bats. Again the most probable difference is the ability to produce backspin. This implies that bat 2 had less ball slippage than bat 1 and because there was less ball slippage with bat 2 greater backspin was produced, which increased the D/B ratio.
 
 

As for the individual balls the balls from manufacturer-2 had much higher D/B ratios than the balls from manufacture-1. Therefore it appears that the aerodynamics are different based on the manufacturer.

The balls from the different manufacturers can also be compared strictly on a distance basis. The average distance for the two balls from ball manufacturer-1 was 334.9 ft, while for the four balls from manufacturer-2 the average distance was 318.0 ft. The balls from manufacturer-1 out distanced those from manufacturer-2 by 5.3%. While for BBS the averages were 91.0 and 89.4 mph for manufacturer-1 and manufacturer-2 respectively. Giving an increase of only 1.8%. This illustrates that the difference in distances obtained from the different manufacturers was most likely due to some difference in the aerodynamic properties of the balls.

Table 4 lists some of the pertinent softball properties that could effect the ball’s aerodynamics. Note that seam heights are not shown in Table 4 because no significant difference was noted in seam heights for these balls.

The resistance due to drag forces is proportional to the cross sectional surface area of the ball. The higher the cross sectional area the more drag forces effect the ball and with all else being equal the ball with higher cross sectional area will not fly as far a ball with lower cross sectional area. Both the balls from manufacturer-2 have higher cross sectional areas than the balls from manufacturer-1. If all else were equal this would imply that the balls from manufacture-1 should have farther distances than those of manufacture-2. However, this was not the case and all else is not equal.

The effect drag forces have on a softball are proportional to the weight of the ball. The heavier the ball the less affect drag forces have on the flight of the ball. This can be easily demonstrated by throwing both a plastic practice golfball and an actual golfball. Because the plastic golfball is so light compared to the actual golfball it will not fly nearly as far as the actual golfball. The weights for the balls from manufacturer-2 are greater than those for manufacturer-1, probably due to the larger size of the balls from manufacture-2. This would indicate that with all else being equal the balls from manufacturer-2 should fly farther than the balls from manufacturer-1, as was seen. However, both the cross sectional area and weight need to be lumped together in order to accurately determine their affect. Since both the effect of area and weight are proportional to the effect of the drag forces these properties can be combined in to a single property, Area/Weight ratio.
 
 

For the Area/Weight ratios shown in Table 4, the lower the ratio the farther the ball should travel. However as shown the Area/Weight ratios are fairly close and do not correlate with the D/B ratios. This is especially true for the 0.44/511 softball that has an Area/Weight ratio very near the overall average and a D/B ration much greater than all Manufacturer-1’s softballs. Therefore it appears that the difference in distances between the balls is not due to size/weight differences.

Ruling out size, weight, and seam height leaves backspin as the most likely cause for the increased D/B ratios of manufacturer-2’s balls. What could allow certain balls to produce more backspin than other balls? Two possibilities are slippage between the bat and the ball or slippage between the cover and the polycore of the ball. Visual inspection of the balls from manufacturer-1 indicated there was some wrinkling of the covers. This may indicate that there was some slippage between the cover and the polycore of the ball for manufacturer-1’s balls during hitting with would account for the lower D/B ratios. No such wrinkling was evident with manufacturer-2’s balls. However, this is far from definitive evidence and it may very well be that the covers of manufacturer-1’s balls slipped more on the bats than manufacturer-2’s balls.

These results prove that balls and bats can be produced and chosen that minimize the danger to pitchers by having safe BBSs, while maintaining good distances for the homerun hitters.

Conclusions

• Batted ball distances did not correlate with either softball compression or COR.
• Batted ball speeds did correlate fairly well with softball compression. The harder the ball the higher the batted ball speed.
• Backspin is a very important aerodynamic factor affecting the flight of softballs. The more backspin the farther the softball travels.
• The type or bounding of the cover affects the backspin produced. The less a cover slips on the bat or the polycore the more backspin produced.
• The surface of the bat is important for providing backspin to the softball. Again the less the ball slips on the surface of the bat the more backspin produced.
• The Reverse Rotation grip is superior for providing backspin than the overlap grip.
• Balls and bats can be produced that minimize the danger to pitchers while maintaining good distances for the homerun hitters.

References

1. “The Effect of Softball Compression and Coefficient of Restitution on Batted Ball Speed,” Michael V. Ciocco and Mark McDowell, Senior Softball Magazine, July, 2002.
2. Standard Test Method for Compression-Displacement of baseballs and Softballs, ASTM Designation F 1888-98.
3. Standard Test Method for Measuring the Coefficient of Restitution (COR) of Baseballs and Softballs, ASTM Designation F 1887-98