Tradition vs. Technology
How Engineering Advances Affect Baseball
Aviel Chang
University of Southern California
May 6, 2013
Abstract
The history of the United States has been significantly impacted by the
presence of professional sports. No sport has embedded itself in this country’s
culture more than baseball. Citizens have been following America’s pastime for
generations and will continue doing so in the many years to come. Fans have versed
themselves with an immense knowledge of the game, ranging from in depth player
statistics to front office strategies. Any enthusiast can agree that baseball is a game
of extraordinary intricacies. Its success is directly attributed to a scientifically
concrete foundation. Designing a regulation bat, glove, or ball requires the utmost
care and precision. The anatomy of a baseball bat best illustrates the multifaceted
nature of the sport. There are two types of baseball bats currently being used today;
one is made of wood and the other is made of aluminum. Each one produces
drastically different results, which is especially apparent once collision has been
made with the ball. This is due to the structural design of each bat. Understanding
this groundwork illuminates the science behind America’s favorite pastime.
Introduction
The game of baseball is played with several core components: the ball, the
bat, and the mitt. A meticulous amount of detail is applied engineering each of these
items, particularly the bat. Perfecting the geometry, the mass distribution, and
especially the material are tasks that play an important role in the creation of any
regulation baseball bat. Any successful hitter understands these aspects and applies
them in his game. Understanding the difference between wooden and aluminum
bats increases the appreciation a fan or even a player has for the sport. Once a
player truly understands bat construction can the rest of his game progress and turn
to perfecting mechanics. The goal of every batter is to make contact at the bat’s
“sweet spot”. Structurally, it is the location where the measured performance of the
bat is maximized and where the stinging sensation of the hands is minimized. More
often than not, fans view hitting to be one of the most exciting aspects of baseball.
By understanding the structural engineering, mechanics, and physics behind every
swing, enthusiasts can attain a better grasp of the way America’s pastime works.
Wooden or Aluminum: What’s the difference?
The baseball bat has gone through minor structural alterations since its
initial design. Keeping with tradition, however, there have never been any major
overhauls. The baseball bat today is primarily made with wood or with aluminum.
Professionals typically use a maple bat, whereas little league and college level
players use aluminum bats. Major League Baseball permits a bat to reach 2.61
inches in diameter at its thickest point, and to reach a maximum of 42 inches in
length. Aluminum bats must weigh 3 ounces less than the length to be eligible for
use in high school and collegiate play. Additionally, they must possess a barrel that
is 2 5/8 inches in diameter. Athletes are allowed to use a variety of bat sizes as long
as they are within the regulations set by their respective leagues.
Wooden baseball bats have been a historical staple in the MLB and remain
the standard to this day. Initially, the majority of players used bats made out of
hickory. However, such material became unfavorable due to its heavy weight and
cumbersome nature. Eventually, players unanimously shifted to ash bats for better
bat control and increased contact frequency [2]. Ash remained the wood type of
choice until Barry Bonds broke the homerun record using a maple bat. Ever since
Bonds’ record-breaking feat, the rest of the league has followed suit in the use of
maple bats. The league values this type of bat because its simplicity symbolizes the
history and tradition of baseball. With wooden bats, manufacturers are virtually
incapable of engineering improvements in actual bat performance [1]. Wood type
will always be the most significant determinant in bat function. There is engineering
in the design of the taper from the barrel to the handle; however, that is primarily an
artistic element rather than any sort of structural alteration [1]. Between identical
models, there are natural variations in weight. This is simply due to disparities in
wood density, with the discrepancies rarely exceeding three ounces [1]. The wooden
bat is a model of consistently that has been a part of American culture for decades.
The most popular brand, the Louisville Slugger, has since become a household name.
Wooden bats help promote a level playing field, which is crucial for a league
embroiled in controversy. Faced with rampant allegations of widespread steroid
use, the MLB cannot afford to institute anything else that could possibly elicit
further cheating.
Wooden baseball bats will always be a part of the MLB, as they embody
simple yet sound structural design. Though manufacturers lack a certain control
over wooden bat production, they possess the ability to shape multiple aspects of
aluminum bat design. Aluminum bats were first created for economical reasons, as
they were inexpensive and lasted longer. Metal is significantly more flexible, which
gives the designers the freedom to work with various alloys and material processing
methods [1]. Manufacturers can shape almost every part of the bat while
maintaining its effectiveness. Wall thickness and the outer diameter can be modified
to affect the modal structural behaviors of the bat, the location of the center of
gravity, and the mass moment of inertia [1]. These are all significant factors that
affect how a bat performs. Aluminum bats feel lighter, and therefore allow hitters to
increase swing speed; naturally, the ball is then hit harder while traveling faster
than ever before [1]. While there are natural weight differences between identical
wooden models, manufacturers control density factors in aluminum bats. As a
result, they are able to monitor the weight of all aluminum bats in order to keep
them light. To further increase the hitter’s swing speed designers lower the bat’s
mass moment of inertia. This is with the intention of maximizing the ball speed after
contact.
The Sweet Spot
There are numerous dissimilarities between the structural designs of a
wooden bat versus an aluminum bat. Something that will never change, in spite of
this, is the impact a baseball makes with a bat in the midst of contact. A baseball
experiences more deformation during collision than a bat [4]. The faster the ball
speed the more deformation transpires; subsequently, the speed of the ball lessens
significantly after the collision. This is measured as the coefficient of restitution,
which is defined as the ratio of incoming velocity to outgoing velocity [4]. Many
professionals put this phenomenon into use their during dugout warm-ups. The
energy from temperature affects the coefficient of restitution, which is why players
warm their bats before coming up to the plate [7]. The energy from heat transfers
into the ball on contact, which increases the likelihood of a long distance shot.
Overall, the coefficient of restitution can help measure the difference in velocity
between balls hit by an aluminum bat versus balls hit by a wooden bat. Every batter
wishes to maximize the outgoing velocity of a hit ball. However, this does not always
result in success; a hard hit line drive could very easily wind up in the hands of a
defender. Years ago this would simply be attributed to bad luck. Nowadays, baseball
statisticians have the ability to document almost every facet of the game. This
includes differentiating between hard hit balls and fly balls.
Contact can happen anywhere on the bat, but every hitter’s desire is to strike
the sweet spot. Attacking the sweet spot maximizes the ball’s outgoing speed postcollision and is measured by the coefficient of restitution. Most bats have a different
location for a sweet spot; the average sees it resting roughly five to seven inches
from the end of the barrel [6]. Hitting this point also minimizes the stinging
sensation typically suffered in the batter’s hands. Many manufacturers insist that
aluminum bats are designed with a wider sweet spot, but that comes without any
significant scientific backing [6].
Regardless of bat type, the center of percussion is a point that has
consistently been recognized as the sweet spot. This position can be identified by
pivoting the bat about a point on the handle six inches from the knob, followed by
measuring the period of oscillation necessary for the bat to swing back and forth
through one cycle [6]. The center of percussion is affected by another important
determinant, the moment of inertia [6]. The distance between the pivot point and
the center of mass also makes an impact formulating the center of percussion [6].
Any collision in this area results in zero net force at the pivot point, and for that
reason minimizes stinging in the hitter’s hands. This is the ideal location where a
batter wants to make contact. Perfectly striking the sweet spot will almost always
result in a well-hit ball. Hitters will also reflect on the degree of pain experienced
during contact. It acts like a reference point, helping them make future adjustments
at the plate.
Consistently attacking the sweet spot is a difficult task for any baseball
player. Typically, hitters make contact with the other segments of the bat. As
collision gets closer to the handle, translational force will increase at the pivot and
hurt the batter’s hands accordingly. Contact closer to the barrel end will cause the
bat to rotate about its center of mass, producing a force in the opposite direction at
the pivot point [6]. When striking a ball in the center of percussion, however, these
two opposite forces become even and will almost always produce a successful hit.
The center of percussion cannot consistently be the sweet spot because it is not a
fixed point on the bat [6]. It depends on the location of the pivot point, which may
vary between bats. When bat and ball meet, the pivot point actually shifts outside of
the handle while the center of percussion simultaneously moves in the same
direction [6]. If this is the case, how can the methods of testing consistently label the
pivot point as six inches? The actual pivot point moves with impact and will often
stray from the six inch point regularly referenced [6]. The factors that determine the
sweet spot are highly variable by nature. They are unique to each player and cannot
be applied on a general basis. While this may be a testament to the unpredictably of
baseball, it also supports the notion of a level playing field.
The sweet spot lacks a truly universal definition. Another popular theory
highlights the position in the barrel end node of the first bending mode of vibration
[6]. This explanation specifically targets the diminishing sting in a player’s hands. It
does not offer insight into how a player should go about improving contact. Collision
away from the sweet spot offers subpar results because the ball looses energy into
bending modes [6]. While theoretically plausible, the reality is that a collision is
simply not enough time to establish any viable vibration patterns. Vibrations are
cultivated by the structure and boundary conditions of the bat itself [6]. Therefore, a
batter’s hands will have no effect on the vibration impulse; its arrival comes after
the ball has already left the bat.
Bat Structure
The structural differences between wooden and aluminum bats run deeper
than simple aesthetic design. Dissimilarities can be identified the moment there is
contact with a baseball. Wooden and aluminum bats alike, the barrel end bends
backwards after contact [1]. This creates strain energy that is transmitted into the
ball after the bat bounces back [1]. The hollow barrel of an aluminum bat creates a
hoop-deformation mode, which adds a pocket of strain energy that is not found in a
solid wooden bat; without any deformation, the wooden bat simply cannot release
as much energy as an aluminum bat can [5]. As the interior walls of a hollow
aluminum bat cave in and retract, vibrations arise in the shape of a hoop or ring [7].
The ring gradually morphs into an anti-node that creates the location of the sweet
spot [7]. The result of this hoop vibration is the development of a trampoline effect
during the 1-to 1.5-millisecond period [1]. First, the flexibility of the hollow
aluminum bat causes less deformation in the ball and as a result conservation of
energy; the energy used to compress the barrel subsequently shoots back into the
ball on the rebound, thus spring boarding it even further [5]. The energy stored in
the deformation of a solid wooden bad is at 2% during collision, where as the energy
stored in an aluminum bat during collision is roughly 10% [2]. The design of an
aluminum bat is naturally engineered to outperform a wooden bat. Altering barrel
diameter, wall thickness, and swing weights are just several tactics manufacturers
use to improve the effectiveness of their product [5].
Conclusion
The phrase “baseball is a game of mechanics” is familiar to most fans of the
sport. While that may be true, it is guaranteed that most can only scratch the surface
of why such a slogan exists. There is no sport other than baseball that is modeled on
such unique conceptions such as structural engineering, mechanics, and physics.
Without these core building blocks, the sport would be in a different place than it is
today. These conceptions have helped define baseball since the very beginning, and
will remain a part of the game in the foreseeable future. Advances in technology can
affect the aluminum bat, but its wooden counterpart will always stay the same.
Professional baseball is permanently associated with this country’s history. It is a
national tradition that will be forever known as America’s pastime.
References
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Baseball Bats Using Experimental and Finite Element Methods.” University of
Massachusetts: Baseball Research Center. http://m5.eng.uml.edu/umlbrc/publications/Characterizing%20the%20Performance%20of
%20Baseball%20Bats%20using%20Experimental%20and%20Finite%20Element
%20Methods.pdf
[2] L. P. Fallon and J. A. Sherwood. “A Study of the Barrel Constructions of Baseball
Bats.” University of Massachusetts: Baseball Research Center.
http://www.uml.edu/docs/A%20Study%20of%20the%20Barrel%20Constructions
%20of%20Baseball%20Bats%20by%20Fa…_tcm18-60852.pdf
[3] L. Smith and J. Sherwood. “Engineering Our Favorite Pastime.” American Society
of Mechanical Engineers. January 2001. http://www.asme.org/kb/news--articles/articles/applied-mechanics/engineering-our-favorite-pastime
[4] D. A. Russell. “Physics and Acoustics of Baseball and Softball Bats.” The
Pennsylvania State University. http://www.acs.psu.edu/drussell/bats.html
[5] A.D. Sutton, J.A. Sherwood. “Using Vibration Analysis to Investigate the Battedball Performance of baseball Bats.” Procedia Engineering. 2 (June 2010) 2687-2692
[6] D. Russell. “The Sweet Spot of a Hollow Baseball or Softball Bat.” Kettering
University. http://www.acoustics.org/press/148th/russell.html
[7] D. Ghista. Applied biomedical engineering mechanics. CRC Press, 2008.