Selection and Performance Rationale of Wood vs. Aluminum Baseball Bats

Authors: Vilas G. Pol¹

AUTHORS INSTITUATIONAL AFFILIATION:

¹Davidson School of Chemical Engineering, Purdue University, West Lafayette, Indiana, 47907, United States

Corresponding Author:

Vilas G. Pol

Purdue University

Davidson School of Chemical Engineering

West Lafayette, Indiana 47906

[email protected]

Acknowledgments

We would like to express our sincere gratitude to Sunkalp Vilas Pol for his valuable contribution to this research. His assistance in this article is greatly appreciated and played an important role in the development of this paper. We commend his dedication and enthusiasm for learning.

Selection and Performance Rationale of Wood vs. Aluminum Baseball Bats

ABSTRACT

USA Youth Baseball approves metal/alloy, composite, and wood (or a combination) bats for use in baseball games. However, players, parents, and coaches often face a dilemma when selecting a superior baseball bat, as bat quality depends on material, durability, performance, sensation, player preference, and balance. The purpose of this experimental investigation is to understand the maximum exit velocity of a baseball and overall performance of maple wood vs. aluminum bats. This is accomplished by hitting a stationary ball on a tee as well as with two different pitch speeds (30 and 40 MPH from a roller pitching machine), measured by a speed radar (accuracy ±1 MPH) in a controlled environment. It is hypothesized that when the material of the baseball bat changes, the exit velocity of the ball would change due to the trampoline effect (compression of the solid metal barrel) when hitting with the metal/aluminum bat compared to the solid wood bat. Apart from similar barrel size, length, and weight of the bats, it is observed that the metallic aluminum bat is slightly superior (2-3%) because of the trampoline effect when the balls were hit off the tee and with the machine at 30 MPH speed. Interestingly, for the 40 MPH automatic pitching machine test, the wood bat was 3-4% superior to the aluminum bat, possibly due to high impact speeds with less than 1 ms impact duration and minimum energy losses in the bat, or even due to the strength of the batter. The data were collected by a 12U youth baseball player in three different sessions for better accuracy and reproducibility. In fact, high-quality (hence expensive) wood or aluminum bats could lead to analogous outcomes (±1-2% variations) when used in a controlled environment, not significantly contributing to winning the baseball game.

Keywords: Exit velocity, Trampoline effect, Barrel size and length, Controlled environment, Efficiency

INTRODUCTION

Baseball is a popular American game played between two teams of nine members with a bat, a ball, and gloves on a diamond-shaped field with alternating batters (offense) and fielders (defense). The batter’s goal is to hit the ball hard enough, putting it out of reach of the fielding team to make a complete circuit around the bases to obtain a ‘run,’ with the team scoring the highest number of runs winning the game. This is typically made of either of wood or a lightweight metal such as aluminum. Now the mystery question is which bat (wood or aluminum) should be selected for such an important task.

During the last century, there has been significant research and development in the baseball field including selection of bats, barrel diameter, shape, length, and composition. Naturally, wood and aluminum bats are considered based on their performance, affordability, and safety. Typically, the more expensive bats use higher quality materials, hence better properties such as lightweight materials leading to longer distances and more power while producing minimal vibrations.

Due to lots of discussion in the open literature arguing which material bats are superior, this study particularly focuses on the experimental investigation of the exit velocity of most common aluminum and wood bats. It was hypothesized that using a maple wood bat versus an aluminum baseball bat of the same length, barrel size, weight, and producers used to strike the ball might create a different exit velocity because of varied physical properties of bat materials, including the commonly known trampoline effect (barrel compresses and expands) while using the hollow aluminum bat compared to the solid wood bat.

In 2022, Sherwood et al. studied five aluminum and wood baseball bats and observed that the field performance of these bats strongly correlated with the ball–bat coefficient of restitution COR. They predicted the relationship between wood baseball bat profile and durability based on finite element modelling of 15 profiles used from 15 MLB players (1). Russell described the effect of cylindrical barrel and flexural bending vibrations (2) on softball and baseball bats with respect to their performance including understanding the sweet spot and the origin of the ping (3) sound. Shenoy et al. predicted a model for the performance of solid wood and hollow metal bats with an experimental agreement for the impact speed, ball types, bat models, and impact locations (4).  It is observed that the energy dissipation between the bat and the ball happens through ball deformation, elastic bat vibration and contact friction (4). In 2002, Sherwood et al. investigated the durability of the wooden bat based on the slope of grain impact and impact location, with statistical analysis and finite element modeling. In other study they predicted the relationship between wood baseball bat profile and durability (5). In 2003, Drane and Sherwood described the effect of moisture content on the wooden bat, increasing the velocity by a maximum of 1% (6). In 2002, Penna et al. described that the exit velocity can depend on the skill level of the player or a higher performing bat (7). The systematic literature review created a knowledge gap to investigate the dilemma in selecting the most effective bat that would contribute in winning the baseball game.

This article methodically answers that question with experimental evidence through carefully measuring and comparing the average exit velocities of an aluminum and a wood bat with reproducibility. Though both bats had similar speeds, exit velocity measurements show that the aluminum bat is 2-3% superior because of the hypothesized trampoline effect when the balls were hit off of the tee and against 30 MPH pitches from the ball roller pitching machine. Surprisingly, for the 40 MPH automatic pitching machine test wood bat was 3-4% superior to the aluminum bat possibly due to less than 1 ms impact duration with the minimum energy losses in the bat or even the strength of the batter. This article provides experimental evidence for 12U youth baseball players that high quality wood or aluminum bats could lead to the analogous outcomes with 1-2% variations when used in a controlled environment.

Methods

A standard pitching machine manufactured by Junior Hack Attack was utilized to set up the velocity of the ball being pitched. The speed radar was purchased from Bushnell with an accuracy of ±1 MPH. The velocity gun was calibrated utilizing the set speed of the pitching machine and reading of the radar to a 1 MPH accuracy. The aluminum bat with a length of 31 inches, 23 ounces, and a barrel size of 2 ¾ inches was purchased from Marucci. The maple wood bat with a length of 31 inches, and a barrel size of 2 ¾ inches was purchased from Victus Nox (The brand Marucci owns Victus Nox). A bucket of standard baseballs was purchased from Wilson. A standard batting tee manufactured by Tanners Tees was utilized for the tee tests. An indoor baseball and softball facility (Lifelong Sports, Lafayette, Indiana, USA) was used for these experiments. Figure 1 depicts all used baseball accessories.

Two different velocities of =30 and 40 MPH were set by adjusting left, bottom, and right knobs of a standard pitching machine (Figure 1). The balls were loaded into the pitching machine by a person with approximately 15 second intervals between the pitched balls. The batter wore the requisite safety equipment (helmet, arm guard, leg guard, and batting gloves) while hitting the balls as they were pitched. The speed radar was set up approximately 4 feet behind the batter and the exit velocity was measured after the bat had contacted the ball. Ten balls were set on the batting tee (one at a time) and hit within 15 second intervals. The handheld speed gun was used behind the batter and pointed at approximately where the ball would be headed. Three trial runs were carried out before the final experiment to find errors in the experiment and to correct them. After hitting ten balls with the aluminum bat, the wood bat was used to hit the next ten balls to minimize the error, assuming that the batter’s strength is similar between tests conducted sequentially. Within each set of experimental conditions, the exit velocity of the balls was categorized and reported as the highest (Hi), lowest (Low) and average (Avg) speeds. In some cases, the aluminum bat’s sound frequencies affected the speed gun measurements. These experiments and speed measurements were repeated. Newly purchased baseball balls were used for the measurements to minimize the error. Please note some of the concerns in wood versus aluminum bats are i) the wood bat breaking could happen due to the ball hitting around the handle area or the end, ii) the wood bat could hurt players’ hands due to high impact speeds and vibrations, and iii) the aluminum bat cracking could occur as the metal shrinks in the cold with unsafe storage.

Results

Typically, commercial baseball pitching machines are arm type (stores balls on sides in an arm shape, which automatically dispenses balls) or roller type (person must manually put balls into the machine). Both machines can dispense different pitches (8) such as fastball, curveball, screwball, slider, etc. To carry out the experiments in a controlled air, moisture, and temperature environment for better accuracy, we used roller type dispenser at LifeLong Sports, Lafayette, Indiana, USA.

Fig. 2 depicts the exit velocity data from 10 balls that were hit off of the tee with maple wood and aluminum bats. The highest exit velocity for the balls that were hit by the wood bat ranges from 57 to 62 MPH, while more consistent 61 MPH for the aluminum bat. The lower velocity and average exit velocity data demonstrate that the effect of using either wood or aluminum bat is negligible when the balls were hit off the tee.

In Fig. 3, 10 balls were pitched at 30 MPH and the exit velocity data was collected for maple wood and aluminum bats. The highest exit velocity for the balls that were hit by aluminum bat ranges from 61 to 63 MPH, while being 55 to 61 MPH for the wood bat. The lowest exit velocity for the balls that were hit by wood bat ranges from 40 to 43 MPH, while 50 to 51 MPH for the aluminum bat. Overall, 2-3% superior performance of the metal bat was observed due to hollow vibrating wall of the bat (similar to a drum upon impact), producing a loud ping sound (9).The exit velocity of the balls was almost double the velocity of balls impacting to the bat. In fact, the wall bends slightly in an inner direction retaining some of the vibrational energy and then coils back after impacting on the bat. The low frequency ping sound (1,000 Hz) indicates softer, thinner wall thickness of metal bat while high frequency (2,000 Hz) ping sound indicates bat wall is thicker, hence stiffer (9). The trampoline effect on the metal bat helps gain a little more speed compared to the wooden bat (9).

At high pitch speeds of the incoming balls (40 MPH), the obtained data show a slightly different trend, as seen in Fig. 4. The highest exit velocity for the balls that were hit by the aluminum bat ranges from 51 to 53 MPH, while being 57 to 58 MPH for the wood bat. The low exit velocity for the balls that were hit by the aluminum bat ranges from 40-41 MPH, while being 41-45 MPH for the wood bat. Namely, the wood bat showed a slightly superior exit velocity compared to the metal bat. This could be due to high impact speeds with less than 1 ms impact duration with the minimum energy percolation in the bat (9). As baseballs from the same batch were used for both the 30 MPH and 40 MPH pitch tests, these differences can be attributed to differences in the bat material rather than the baseballs themselves. In these conditions, a solid wood bat could perform better than the thin-walled metal bat because of minimized trampoline effect. The wood bat does not ping as loud as metal meaning that it imparts most of the stored elastic energy to the ball with less energy left in the wall of the bat to vibrate (9). Other possible reasons the wood bat was better with enhanced exit velocity are hitting with the harder grain or the shape of the balls (possibly deformed on the harder wood bat), and differences in manufacturing of the bats. These reasons also support why the wood bat performed superior in the 40 MPH test. When 10 balls were hit on both bats with 30 MPH and 40 MPH pitches, the measured exit velocity ranged from 40-63 MPH at low, medium and highest velocities confirming that most of the stored energy is returned to the ball without significant dissipation.

Discussion

The trampoline effect describes noticeable elasticity in objects impacting at high speeds with applicability to sports such as baseball (the ball and bat), golf (the ball and club), and tennis (the ball and racquet) such that they act like a spring analogous to when we jump on the trampoline and get bounced back. In baseball, the elasticity of a bat upon the impact of baseball is different for wood and aluminum bats. Typically, when the baseball hits a wood bat, the ball compresses losing more than half of its energy, but when using a hollow aluminum bat, the bat compresses rather than the ball.

The fundamental physics understanding of the trampoline effect in baseball and softball bats was documented by Nathan et al. two decades ago (10) who identified that upon the high-speed impact between a bat and baseball, the original center-of-mass kinetic energy is transformed into compressional energy. Certain energy is stowed in vibrational modes (hoop modes), providing this stored energy to the baseball with minimum dissipation of energy with larger ball exit velocity due to the trampoline effect (10). In other words, the elasticity of a bat upon the impact of baseball determines the magnitude of the resultant trampoline effect (Fig. 5). Typically, when the ball impacts on the aluminum bat, because of its hollow nature the bat barrel compresses to lose energy and returns it to the ball soon after. On the wood bat, the ball compresses and loses up to 75% of energy in frictional forces (10). Typically, during the bat-ball collision, the exit velocity of the ball would be dependent on the effective mass/weight of the bat. However, this is a negligible effect in the experiments reported in this work as both bats possess similar masses. The exit velocity is at its peak at the place on the bat where maximum power was applied on the surface of ball, storing more elastic energy, and subsequently imparting it back to the ball (9).

Conclusions

Controlling for the barrel size, length, and weight of the bat, it is experimentally measured and observed that aluminum bat is 2-3% superior when balls were hit off of the tee and against 30 MPH machine-pitched balls because of the trampoline effect. Remarkably, for the 40 MPH automatic pitching machine test, the wood bat was 3-4 % superior to the aluminum bat possibly due to high impact speeds with less than 1 ms impact duration with the minimum energy losses in the wood bat or even the strength of the young batter. Even though both bats had similar speeds, exit velocity measurements were measurably different. Therefore, it can be concluded that high quality wood and aluminum bats could lead to analogous outcomes when used in a controlled environment.

Application in Sport

The outstanding performance of a baseball player can be highly dependent on the selection of a metal or wood baseball bat, its balance, durability and feel in addition to the player’s capabilities. In general, metal bats are known to provide enhanced power, durability, and a broader sweet spot while wood bats provide a traditional feel, tailoring options, and a smaller sweet spot. This article offers insight into the rationale behind selecting a bat with peace of mind for the player, parent, and coach corroborating that high quality (hence expensive) wood or aluminum bats could lead to analogous outcomes with 1-2% variations when used in a controlled environment. Eventually, use of a metal or wood baseball bat is a personal choice, guided by player strength and abilities.

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