Acoustics and Vibration of Baseball and Softball Bats

“Acoustics and Vibration of Baseball and Softball Bats,” Acoustics Today, 13(4), 35-42. https://acousticstoday.org/acoustics-vibration-baseball-softball-bats-daniel-russell-2/

Author: Daniel A. Russell

Published: Winter 2017

In this episode, we speak with Daniel Russel of the Graduate Program in Acoustics at The Pennsylvania State University, about his article, “Acoustics and Vibration of Baseball and Softball Bats,” which appeared in the Winter 2017 issue of Acoustics Today. In this interview, we discuss all the ways acoustics and vibration affect a bat’s performance, including how the bat’s sound relates to its performance, the physical properties that create the “sweet spot” of a bat, and the role vibration plays in cheating attempts.  

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Intro/Outro Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022

“Take Me Out to the Ballgame” played on baseball bat piano, courtesy of Daniel A. Russell. See the full video at https://www.youtube.com/watch?v=r4KTGj-2trQ&t=1s.

Transcript

Kat Setzer (KS)

Welcome to Across Acoustics, the official podcast of the Acoustical Society of America’s Publications Office. On this podcast, we will highlight research from our four publications, the Journal of the Acoustical Society of America, also known as JASA. JASA Express letters, Proceedings of Meetings on Acoustics, also known as POMA, and Acoustics Today. I'm your host, Kat Setzer, Editorial Associate for the ASA.

[Musical interlude: “Take Me Out to the Ball Game” on a piano made of baseball bats.]

KS

01:03

That rendition of “Take Me Out to the Ballgame” was played by our guest on today's episode, Daniel Russell of the Graduate Program and Acoustics at The Pennsylvania State University. What you may not realize is that he performed that song using a piano made entirely of baseball and softball bats. Today we'll be discussing his article, “Acoustics and Vibration of Baseball and Softball Bats,” which was published in the winter 2017 issue of Acoustics Today. Thank you for joining us today, Dan. How are you doing?

Dan Russell (DR)

01:26

I'm doing great. Thank you so much for having me on this program.

KS

01:29

We're really excited to have you. First, tell us a little bit about your background.

DR

01:34

So I have a bachelor's degree in piano performance and a bachelor's degree in physics from Bradley University, and the combination of piano and physics was what got me into the field of acoustics. I did a master's degree in applied physics from Northern Illinois University, studying with Tom Rossen, who's an expert on the acoustics of musical instruments. And my master's thesis had to do with the physics of piano hammers, marrying my love of pianos and physics together. Then I got my PhD in acoustics from Penn State, focusing on structural vibration. Then after graduating, for 16 years I was on the physics faculty at Kettering University in Flint, Michigan. That's where I started doing research on baseball bats and sports equipment, where my students gave me the nickname “Batman,” and then for the last 10 years, I've been on the acoustics faculty at Penn State.

KS

02:20

Awesome, thank you. So what do acoustics and vibration have to do with a baseball or softball player’s choice of bat?

DR

02:29

Well, surprisingly, this is a surprise to me, the three things that most strongly influence player perception of any handheld sports—baseball, softball, tennis, golf clubs, anything that involves a handheld object hitting a ball—the three things that matter the most are the sound that the implement makes with impact on the ball, the way it feels in the hands after impact, and the perception of the initial path that the ball takes. So the sound and feel are the two things, that if it doesn't feel right doesn't sound right, a player doesn't want to use that bat/racquet/club, regardless of whether or not that bat, racket, or club hits the ball. Well, it's the sound in the field that are the most prominent determiners of whether a player really likes this bat, or that racket or that club.

KS

03:17

That's really interesting. So what are flexural bending modes, and what do they have to do with bat performance?

DR

03:26

So the entire bat can bend along its length, kind of like if you were to take a ruler in your hands and flex it, you know, put a hand at each end of the ruler and bend it to try to flex it; a baseball bat will do the same thing. It's kind of like the way that a string on a guitar vibrates when you pluck it. And a bat has a large number of vibrational mode shapes, ways that it will bend back and forth, up and down along its length. Each of those shapes has a unique frequency. And as the bat vibrates, each of those individual shapes that it vibrates with has points along the bat where there is no vibration. We call them nodes. And essentially, it's on one side of that node point the bat’s moving up, and on the other side the bat’s moving down. And so that point in the middle is the point that doesn't move while the bat kind of that, that location, the bat kind of rocks back and forth around that point. Those node points on the bat are what have to do with this thing we’ll later on talk about, a sweet spot. These flexural bending modes play a role in defining the sweet spot of the bat in terms of feel. Because if you hit the bat at one of the places where the bat doesn't vibrate, then that particular vibrational shape and that particular frequency won't get excited.

KS

04:38

Oh, interesting. Okay. So how do you study vibrational mode shapes and frequencies in the lab?

DR

04:46

So in the lab, I used an experimental technique called “experimental modal analysis.” I take a really small, tiny accelerometer, a device that measures vibration, and I attach it, usually with wax to the barrel, near the end of the barrel, and then I strike the bat with a special force hammer that measures the amount of force when you impact it. Then I use a frequency analyzer to capture something called the “frequency response function.” That is a ratio of the acceleration, the vibration at one location on the bat, due to a force impact at another location on the bat. And then that frequency response function provides me with information about the frequencies that which the bat vibrates the relative direction and amplitudes of the vibration at the measurement point. And if I collect a whole bunch of pairs of these points along the length of the bat, I use special software that takes all that data and then curve fits it and then produces animation showing me how the bat structure as a whole vibrates at each of those different unique frequencies.

KS

05:45

Wow, that's really cool. Interesting. So how well does what you do in the lab correlate with what actually happens when a person is swinging the bat on a baseball field?

DR

05:56

So we use this information about the bending vibrations and the bending frequencies to help understand how players sense the feel in their hands, and especially the sense of sting. Most people who've played baseball, especially when you're a kid, would remember hitting the ball badly, and your bat stings and your hands hurt. You shake your hands after a bad hit. The reason that it hurts in the hands is because the bat is vibrating in some of these flexural mode shapes. And so understanding how the bat vibrates, understanding where on the barrel should I hit the bat so that it doesn't vibrate, and understanding what frequencies is the bat vibrating with, it helps us understand what's going on in the hands of the player. That the complete relationship between what I measure in the lab and what is measured in the field, we're still studying that, trying to get a sense of exactly what makes a player think the bat hurts or doesn't hurt or what makes them feel that they like the weight feels better than others. But I have worked with a number of manufacturers to develop for aluminum and composite bats to develop vibration absorbers that remove the sting, remove the vibration for badly hit balls, so that little kids, when they're playing don't get stung every time they hit the ball badly. And those have tended to work out pretty well.

KS

07:09

That's really neat. Um, so how do bats’ bending frequencies vary based on the types of materials used?

DR

07:18

So the thing that determines the frequency of a bat—two properties—frequency is always determined by mass and stiffness. Those are the two properties that determine the vibration frequency of any object. Mass for most bats is not that different; most bats have a weight about the same value, but the material that it's made out of has a big impact on the stiffness, big influence on the stiffness of the bat. So aluminum bats, for example, tend to have much higher frequencies than wood bats. Because aluminum is a much stiffer material with a higher elastic property, a stiffer elastic property—we call it a Young's modulus, a higher Young's modulus of the material— so that aluminum bat will have a much higher frequency than a wood bat. Composite bats are unique or interesting because you can design the composite material to have a pretty wide range of stiffnesses. So you can make a bat that has the same weight but has a, pretty much a large variation in the amount of flexing or the amount of flexibility, the amount of stiffness that the bat would have in the handle. So a lot of manufacturers will make a variety of bats that have stiff handles or flexible handles out of composite materials depending on player preferences.

KS

08:26

Oh, that's really cool too. So do bats have to be just wood or aluminum? Could you use a plastic bat, for instance? And again, would these have any advantage?

DR

08:37

So Major League and minor league baseball require bats to be made from a single piece of wood. NCAA, college, youth baseball, high school, youth baseball, Little League Baseball those allow bats have a lot of variety of materials, so you can use aluminum bats, composite materials; there are not as many rules in terms of what it can be made out for those leagues. So youth bats, college age, high school youth bats, there are bats that are one piece aluminum, there are bats that are two piece aluminum— so aluminum barrel, aluminum handle, attached in the in the middle—there bats that are aluminum barrel with a composite handle, bats with a composite barrel and a different composite handle. Lots and lots of varieties of, you can have a bat that has it the same barrel but has a composite handle that's either stiff or flexible depending on player preference. You asked about plastic bats. I do have a couple of prototypes that are made of nylon plastic. They hurt really badly, so they never made it into production because they have such a strong vibration that they just, they hurt almost to the point that you're you can't pick anything up afterwards, playing it.

KS

09:47

Okay, so this kind of ties into that. Can you use a multi-material bat, then?

KS

09:52

So for Major League and Minor League, no. It has to be one piece of wood. But for every other league of the sport, from high school, college, all the way down to youth, you can use pretty much, you know, there's I don't think there's any rules as to what it can be made out of. There are woods, there are bats that are, you know, aluminum barrels/composite handles, there are bats that are all composite single piece, composite single piece aluminum, there are bats that have—I've even seen a bat that has a bamboo hitting, bamboo solid barrel, and an aluminum handle. So the advantages are wood bats—so we see this in the Major Leagues—quite often a wood bat will break in the handle. And pitchers who knows this will sometimes try to pitch inside to make you hit the ball in the inside in the middle of the bat, which makes it break more likely. So there was a study a number of years ago looking at maple bats, which were having a huge problem with shattering and breaking upon impact. And so they're trying to figure out why maple bats were breaking; it has to do with the grain structure and the alignment of the grain in the wood bats. Aluminum bats don't break in the handle, at least very, very rarely do they break in the handle, so you they you don't have to worry about hitting and breaking your bat when you're playing with aluminum. That's the big difference between the two.

KS
11:02

Okay, that makes sense. Yeah. So we talked about this a little earlier, what exactly is the “sweet spot” in a baseball bat and what causes it?

DR

11:09

So depending on who you talk to, there are at least two different definitions of a sweet spot for baseball bats. It’s similar with tennis rackets as well. One of the definitions is it's a location on the barrel where the ball leaves the bat with the fastest speed. The other definition that's really important is it's the location on the barrel where an impact results in the least amount of vibration in the handle. Most of the time, those two points on the bat, those two locations are very close together, but they're not always the same location. You can design the bat to move those two parts, you know, independently of each other, depending on how you design the weight distribution, the shape profile of the bat, and its material properties to determine its frequency. Usually though, those two sweet spot locations are within a couple of inches of each other, but they're within the width of a baseball of each other. So we talked about a “sweet zone,” rather than a “sweet spot,” because it's not like a point on the bat, it's a range of about between five to seven inches from the end of the barrel, is the spot that if you hit it there, the ball will come off relatively fastest, and it will cause the least amount of vibration in the handle. So we call it a “sweet zone,” about five to seven inches from the end of the barrel, doesn't make the bat vibrates and the ball rebounds with the largest velocity.

KS

12:27

Okay, that's really interesting. So what about the “crack” of a wooden bat or the “ping” of an aluminum bat? How does the noise of the baseball bat relate to the sweet zone?

DR

12:38

So let me just demonstrate that sound for listeners at home too. So I can't swing in my lab without hitting balls and breaking things. But I can take a bat and hold it. [DR hits wooden bat with ball.] So that's the crack of a wood bat, as opposed to—[DR hits aluminum bat with ball.]—the ping of an aluminum bat. And there's lots of people out there who hate the “ping” sound, they just detest that sound. There was, there are sometimes when in the early 1990s, when some different materials came out, that a titanium softball bat was introduced. [DR hits titanium bat with ball.] That has a very, very uniquely different sound that really bothered a lot of players. Composite bats tend to have a little bit different sound—[DR hits a composite bat with a ball.]—more of a pop than a crack. And there are players that can tell the difference on, in even in the in the field of playing. You asked what it has to do with the relationship to the sweet spot. Wood bats with solid barrels tend to make the crack sound. And there is a difference. If you listen really closely, when you hit it at the sweet spot, the crack is a bit more crisp, a bit sharper. I'm not using the right words to describe the sound. But it's it is a little bit clearer crack than if you hit it at the end or the inside of the sweet spot. A good fielder, a player who's been in, you know, the Major Leagues for a while, without even able to see the contact can usually tell whether it was a well hit or poorly hit ball, just by the sound alone. In fact, there are some players that will use that initial sound of the impact, the initial crack sound, to help them figure out in the outfield, do I run in towards the bat, you know, the infield, or do I run out, you know. They can tell just by the sound of the bat, whether I should move in or move out to tell whether it's going to be a far hit or a long hit ball. Before they start looking at their visual clues to figure out where the ball is actually going, they can use the sound of the bat. To do that with aluminum bats, it's a little bit more difficult because anywhere along the barrel that you hit the aluminum bat, you're going to get the same ping sound. So there's less difference in the ping, really doesn't depend on the sweet spot, it's going to be there wherever you hit it on the barrel for an aluminum bat, which is a little different than the wood bats. You can kind of tell a difference for wood bats, but you really can't tell a difference for an aluminum bat, where you hit it compared to the sweet spot.

KS

14:54

Okay, that's really interesting. Now, I'm not much of a sports person, but I'm pretty sure that there aren't any hoops or trampolines in baseball, but you do mention the trampoline effect and hoop mode and your article. So what are those?

DR

15:09

So the trampoline effect is a, it's actually a carryover from golf clubs, golf drivers. So back when, when hollow metal drivers began to replace old wood drivers, solid wood drivers, it became apparent that the face of the hollow golf club, the hollow driver, acted like a trampoline to launch the ball after impact. We  call it a “trampoline effect” because when you're jumping on a trampoline, you can jump a whole lot higher than if you try to jump on the ground. You jump on the ground, it's your legs that are pushing you up; when you jump on a trampoline, it’s the trampoline that's actually throwing you up in the air. So the understanding was from golf clubs is that when the ball hits the face of the golf club, it was the face of the club that was actually springing, acting like a spring, launching the ball forward, rather than it just rebounding with the ball itself. So when a ball hits, when a baseball hits a solid wood bat, if you've ever seen high speed footage of this, there's a couple of YouTube channels that do high speed things that show really cool videos of this. When a ball hits a wood bat, the ball squishes to about half its size, and it loses about half of its total energy during that compression, squishing, due to heat and internal friction. And when it rebounds, it comes off with a velocity, but it's not nearly as great as it would, could if it didn't squish and lose all that energy during the collision. When the ball hits a hollow cylindrical bat barrel, like an aluminum bat, or a composite bat, the barrel squishes like a trampoline. And so the barrel squishes, which means the ball doesn't squish as much. So when the spring, the barrel springs back, it throws the ball forward, and the ball actually can leave the barrel with much higher speed because the barrel is launching the ball rather than just the ball bouncing itself. There have been, you can visualize this, the trampoline effect, in the hoop mode. The hoop mode. I mentioned this thing called the “hoop mode.” The hollow cylindrical barrel of a bat has its own family of vibrational patterns, vibrational mode shapes, just like the whole barrel will bend and flex. That causes these bending vibrations that lead to the sting and the sweet spot. The barrel of the bat will vibrate in a whole bunch of ways, and the easiest way to visualize is to take a styrofoam coffee cup and to squish it. When you squish like the top and the bottom of the cup, the sides bulge out. And then if you squish the sides in, the top and the bottom bulged out. That's what the barrel is doing. In this lowest frequency barrel, cylindrical barrel vibration pattern, we just we call it a hoop mode, because it kind of looks like a hoop as it vibrates. So the entire barrel is squeezing and squishing that way. And this hoop frequency, this trampoline mode, allows us to understand the basic physics of how the barrel and the bat interact with, the barrel and the ball interact with each other during a collision. So we do a simple model—we model it theoretically as a mass spring system, and the ball has a mass and a spring part to it, and the barrel, the hoop mode, the lowest frequency vibration mode of the barrel, has a frequency and mass spring like behavior to it, and the springiness is what helps throw the ball, launch the ball afterwards. There have been some manufacturers of composite bats. With composite materials you can design that hoop frequency, that hoop mode, pretty much however you want to. There are some bats that are extremely high performing; most are illegal for play now because they hit balls too fast. So in college baseball right now, composite aluminum bats have been regulated, so that whatever trampoline effect is there is almost zero. So aluminum composite bats in NCAA college baseball have to perform pretty much the same as wood. So there's really no hitting advantage from a trampoline effect. Now, that hoop frequency, I think I mentioned the “Take Me Out to the Ballgame” video at the beginning of the interview. The hoop frequency of a hollow barrel can have a wide variation. I've got bats in my lab with hoop frequencies as low as 1000 hertz in some frequencies as high as 3500 hertz. So there's a large number of them, you can have a large variation. So here's two— [DR hits two different composite bats with ball, playing slightly different tones.]— that musical person would identify that almost as a semitone. So there's the difference in those two frequencies. So when I in order to make that, in order to make that bat piano, I just grabbed enough baseball/softball bats out of my collection that I had enough frequencies to make an entire musical scale. And then I clamped them all by the handle and just tapped the barrels, and I had enough that I could actually play music with these bats. 

KS

19:47

That’s so fun. That's really cool. So how does hoop mode frequency relate to actual performance?

DR

19:54

So first of all, the hoop mode is what makes the ping sound; that that ping for an aluminum bat is purely because of the of the hoop mode. And you can tune the frequency of that cylindrical vibration that we call the hoop mode, so that the vibration of the barrel almost exactly matches the contact time with the ball. So you can play around with the material properties. And you can tune that frequency so that it's vibration, normal natural vibration, is about the same as the amount of contact time that the ball is in contact with the barrel during a collision. And if you do that, you get a really, really high-performance bat. All those bats that can do that well are illegal, so that we've discovered this, you know, manufacturers, as we're figuring out how to do this and understand the physics of the bat, the bat ball collision, we know how to make a an extremely high-performing bat. They're just not legal for play in any league because they just hit balls way too fast. So most any bat that you could buy in the market right now is not going to be tuned for maximum performance, because it just it makes the balls come off the bat way too fast. The basic idea is that the softer the spring, the softer the barrel, to an extent, the better it's going to catch the ball and throw it back. So bats with a lower hoop frequency, tend to hit balls faster, if everything else about the bat is equal. Currently, the NCAA uses what's called a BBCOR standard, the bat ball coefficient of restitution, they, they fire, baseballs out of a cannon at about 160 miles an hour towards a bat, a baseball bat that's in a, it's clamped in a handle that's allowed to pivot. So the ball gets shot out of a cannon, hits the bat, the bat swings backwards, the ball rebounds, you know, back in the other direction, and they measure the incoming and outgoing ball speeds and the bat rebound speed. And they can determine this thing called this bat ball coefficient of restitution. It's effectively an elastic property of the bat-ball together. And they regulate that. And currently, they are regulating it so that a, a certified bat that's allowed for playing NCAA college baseball, and high school baseball, has to perform essentially the same as wood. So there's no effective trampoline effect that gives you an advantage over a wood bat. It still has a ping sound; it's a very high-frequency ping sound, usually around 2000 to 2500 hertz. The bats that hit the balls really, really well are the ones with frequencies around 1000 hertz, and those are just not legal for play anywhere anymore.

KS

22:25

Okay, that makes sense.

DR

22:26

So if I have if I have two bats, so when I when I go to sporting goods stores, you know, I, my kids and my wife always think I'm crazy, because I'll be picking up bats and tapping them. Because if I can, if I can hear the sound that the bat makes, then you know, comparing two bats, I can usually tell you which one's going to perform better, which one's going to hit the ball faster, just by listening to the sounds of what the bat does.

KS

22:48

Okay, so would that be, then if it's a higher ping, it's a…

DR

22:52

So higher ping is, is a worse bat. A lower ping is the better bat. But most of the bats you'll find in the stores today are going to be within a pretty small range because they're all regulated to be legal. So there's not a lot of variation anymore in what's possible. In softball bats, it's a little bit more variation. A few years ago, 10 years ago, there was a lot more variability out there and the amount of in the hoop frequency you can find for bats on the market.

KS

23:18

Okay, interesting. Does the trampoline effect have anything to do with the corked wood bat or other ways Major League Baseball players try to cheat?

DR

23:28

So the last high-profile Major League Baseball player that I'm aware of who got caught with a cork bat was Sammy Sosa; I think that was back in 2003. And he had a bat that had a hole drilled in the, in the barrel, along the length of the barrel down the center. Actually it wasn't quite the center it was drilled off center, which made it a really even worse thing. But it was a hole drilled along the center. And the idea is that if you, the idea for that was that if you drill the hole out you make the barrel somehow more springy. We didn't have his bat, but we have tested bats wood bats in the lab, with and without holes drilled down to center, with and without cork filled in the holes, with without super balls filled in the holes. And the results of the tests, we do the same kind of testing that we do to test all the other baseball/softball bats on you know, on play, the same kind of tests in Major League Baseball uses to determine bats, the same tests that NCAA uses determine the performance of bats. And we found absolutely no improvement with a corked bat. In fact, the corked bat actually hit balls worse, because there was less weight in the barrel, so it didn't have as effective a collision with the with the ball. So it actually performed worse. So it's very much a psychological thing, that if a player thinks they're modification, modified bat is going to help them swing better, then maybe they will probably swing better and maybe they'll be more confident maybe make contact with the ball more. The problem where we really see a lot of cheating is not in Major League Baseball, it's in amateur softball, especially men's slow pitch, and youth baseball now, because players are taking these composite bats that are that meet the standards and are legal for play. And they'll do something to it to modify that. Sometimes they'll take off the end and they'll shave out the inside of the bat and lathe it to make the walls thinner, make the hoop frequency lower, make the barrel more springy, so it'll hit balls faster. And some of them are getting very creative at ways of trying to break in their bats or alter the stiffness of the barrel to try and lower the hoop frequency or effectively increase the spring performance. So I have had some students in the past that have been working on ways of detecting it, a little handheld device that would actually measure the hoop frequency to try and detect an illegally altered bat. There's a number of other techniques out there. But it's a huge problem with the Amateur Softball Association trying to detect and and police these illegally altered bats that try to make the hoop frequency and the trampoline effect stronger, better by doing something to the barrel to change its performance.

KS

26:01

Oh, that's really interesting. So do bats have to be axisymmetric? Can they have an off-balance weighting? And if so, what would be the advantage?

DR

26:11

So axisymmetric, I think that we're talking about around the circumference of the bat. Bats have to be cylinders, has to be a cylinder, circular cross section in the barrel. And I think that's true across the board anywhere. I have seen some historical bats from the early 1900s that had like a triangular, so it had a flat face. But that's really hard to make sure you're hitting the bat and the ball in contact and not hitting it wrong. So bats always have to be circular. The handle does have some options, though. So the handle of the bat doesn't necessarily have to be triangular, there is an axe-handle shaped bat that allows you to grip the handle a little bit more like an axe handle. So it's, the grip is a little different. There are some grips on the handle that have like a V shape, so you can put your knuckles in your fingers in a certain position. So the handle has some variety, but the barrel of the bat has to be has to be circular. And it really there wouldn't be any advantage to weighting around the circumference of the bat. There are, there are ways that you can weight, change the weight along the length of the bat, but there would be no advantage of doing something around the circumference of the bat. In fact, a lot of times players will try to soften up the barrel of the bat to try and make it soft at a point. That's what tends to make composite bats break, is if you hit—usually on a composite bat, you want to rotate the bat slightly. And you're, in fact, I think some manufacturers actually have little dots on the handle to help you rotate the bat, so that you're not hitting on the same point on the barrel, every impact you kind of even it out around the circumference. So, you make the bat perform uniquely well all the way around, not just at one location.

KS

27:44

Okay, yeah, that makes sense. So what about the weight distribution from the handle to the far end? How much can that vary? And again, what are the advantages if there are any?

DR

27:54

So that that's a one of the ways that you'll find the most variation in bats right now. It really doesn't have anything to do with the acoustics and vibration of the bat, but it does greatly affect the way that the bat performs and swings. So one of the things that matters the most about how fast a bat can hit a ball is bat swing speed, how fast the player can swing the bat, how fast the bat is moving at the moment it impacts the ball. That's a huge predictor on—you want to hit balls faster, strengthen up, bulk up so you can swing the bat faster. So that's one way. The faster you take a given bat to a you know, identical bat, two people swinging it, the person who swings the bat faster will hit the ball faster and farther. Okay. Secondly, if you, the bats have weights, but the weight is not uniformly distributed; it's a thin handle and a thicker barrel. And you can actually, even for wood bats, you can modify things so that you some players will do a little cup out of the barrel of the bat, um, but especially for composite/aluminum bats, you can vary the weight distribution along the length of the bat quite a bit. So I have, I have two bats, the two extremes that I have in my lab are, they're both 34-ounce bats. So they have the same total weight, same total mass. The balance point, or the “center of mass” for a physics term, the balance point would be the place where you get, you know, put your finger up and balance the bat and it would just balance on your finger while you're holding it in front of you. That point on the two bats is four inches different. So one bat that bounce point is four inches further away from the handle, further toward the barrel end of the bat, than the other one. So even though they have the same weight—  In baseball, we talked about a swing weight. What does it feel like when you swing? The swing weight. In physics, we call it a “moment of inertia.” It's the relationship between where the mass, not just how much mass, but where is that mass compared to the pivot point in your hands when you're trying to swing the bat. The further away that balance point is from your hand, the harder it is to swing the bat. The more difficult it is to swing the bat. But the farther away the weight that mass balance point is from your hands, the more effective it's going to hit a ball. So that's the trade off. More, we call an end-loaded or balanced bat. A bat that is end loaded has more mass toward the end of the barrel, so it's more difficult to swing. So you can't swing it as fast, but it hits the ball more effectively. So for a lot of players that trade off completely washes out. And that's why the NCAA uses this bat-ball coefficient of restitution, they measure the barrel stiffness, the barrel properties, the hoop mode property, because the swing speed is offset. If you, if it's too heavy, you can't swing it fast enough, which means you're not hitting the balls effectively. So a really strong bulked-up player will take as end-loaded a bat as possible and swing it as fast as they can and you'll hit the ball faster and farther.

KS

30:53

Okay, cool. That's very interesting. Well, fantastic. Thank you again for joining us today. It was great having You want to Across Acoustics. I'm sure our listeners will be very happy to learn so much about the acoustics of the baseball bats.

DR

31:06

Thank you so much for having me. This is a lot of fun. I enjoyed it very much.

KS

31:14

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