Short Wave - The Peculiar Physics Of Wiffle Balls

Episode Date: April 6, 2020

Wiffle Balls are a lightweight alternative to baseballs, better suited for backyards then sports stadiums. The design of the Wiffle Ball guarantees you don't need a strong arm to throw a curve ball. But how does that happen? Engineering professor Jenn Stroud Rossman explains.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, everybody. Maddie Safaya here with Shortwave reporter, Emily Kwong. Hey, Maddie. Hey, Kwong. Are you ready to have some fun today? Heck yeah. We need it. Yeah, 100%. These past few weeks of social distancing have felt like an eternity. But spring is here. Yes. The season of bees, pollinating flowers, freshly mowed lawns,

and even now, my favorite, final exam season. Which, with many colleges and universities, canceling in-person teaching in response to the coronavirus, many classrooms have gone digital. Jen Stroud-Rosman is a professor of mechanical engineering at Lafayette College, and she and her husband, who is also an engineering professor, they tricked out their dining room with wooden slabs nailed together to keep the cameras straight for streaming their lessons. Not to mention an array of laptops, whiteboards, class notes, and mulberry. multiple cups of coffee. You're all set up. Good job. How long did it take for you to finalize the mobile classroom, the remote classroom in its final form? I mean, it's iterative, like all engineering design, right? So we might tweak it at any time and continue to prototype it. Classic engineering professor. Always prototyping. It's true. So Jen's specialty is fluid mechanics,

basically the behavior of liquids and gases. And her research focuses. on how blood flows through the body, where it slows down and where it starts swirling. Yeah, so I definitely always bring this up at parties. And strangely, whoever I'm talking to gets really thirsty and suddenly breaks for the bar. Who are these people? Why wouldn't you want to learn about blood physics? Well, luckily, ducking out of knowledge is not an option for Jen's undergraduate engineering students. So years ago, she figured out a way to make this whole topic more interesting by getting hands-on. I love baseball.

So I'm always looking for ways to share things I love with students, period. But the fact that I also love fluid mechanics meant that I was looking for ways to get students excited about fluid mechanics. And her teaching career is notable for combining the two. It started with baseballs, but Jen soon embraced the wiffle ball. And in 2002, she began using wiffle balls to teach fluid mechanics. Love it. To undergraduates and run experiments in a wind tunnel. So we're talking wiffle balls like baseball style plastic balls with holes in it?

Yes, but only the officially trademarked wiffle balls with the rectangular holes on just one side that are suited for backyards than stadiums manufactured in my home state of Connecticut. Weird, weird flex, but okay, go on. Listen, it's one of the few things I'm proud of being from Connecticut. it. But what's interesting about wiffle balls is you don't need a good pitching arm to make them curve, but not even the manufacturer knows the science of why. Their website says with a wink, quote, to this day, we don't know exactly why it works. It just does. Honestly, sounds like a research question. Exactly. A research question that Jen and her students tackled head on. So today on the show, the science of an American pastime, how one college,

professor and her students cracked the peculiar physics of the wiffle ball curve. Okay, Kwong, so I want to start with a brief history of the wiffle ball because where I grew up in Ohio, our favorite sport projectile is that little Nerf football that you throw and it screams as it goes through the air. You know what I'm talking about? Sure. Well, in Connecticut, my dad and I played this great game where I'd pitch him a wiffle ball and the goal, the only goal, was to hit it over the house and said me chasing after it. And you got screwed in this game, Kong. But that sounds right to me.

So who came up with these? So the story goes that in the summer of 1953, David and Malaney was watching his son pitch a perforated plastic golf ball in place of a regular baseball because they were nervous about breaking the windows. I mean, been there, go on. And his son's arm, it started aching from practicing some of those trick pitches you see in baseball, sliders and curveballs. And coming out of the post-war plastics boom and out of work himself, David Mullaney wanted to come up with a lightweight alternative to a baseball that would protect his

son's arm. Apparently, he was a semi-pro pitcher, so he had a sense of what to do. Honestly, what a good dad. Right? So he got plastic parts used to package perfume bottles, of all things, cut holes in it, and play tested different versions with his son. And they agreed that the ball with eight oblong holes on one side, that are kind of rectangle shaped, but with a rounded edge, worked the best. And the wiffle ball was born, and its design has not changed since 1953. Gotcha. Okay, so how exactly does the ball curve?

Well, if you look at the instructions inside the box, you'd see that it all depends on how you throw it, and which way the holes are facing when you do. For a curving up shoot, deliver sidearm with a wiffle holes on the top. For a major league drop, pitch sidearm with the holes on the bottom. It's that simple. Kwong, what is this? This is from my 1960 Wiffleball commercial with Yankees pitcher Whitey Ford, showing off the different pitches. Because what's remarkable about the wiffle ball from a physics standpoint is that the holes are on one side, right?

And so if you throw that properly, you're going to get this asymmetry in how the air flows around the ball. and that is going to result in the ball having a force on it that makes it go a different direction. Asymmetry. That's what makes the wiffle ball so dynamic. And a person who isn't super strong able to throw tough pitches and to curve the ball, Jen's favorite is when you point the holes directly at the batter and try to release it with as little spin as possible. Because the holes do disrupt the airflow around the ball, and because the wiffle ball is so very light, that is an extremely unstable trajectory. And so that's how you throw a knuckleball with a whiffle ball.

It just bobbles and dances all over the place in a much less predictable way than the other trick pitches. Wow. Okay. So whiffle balls curve, all kinds of ways. But like how? Because you mentioned earlier, you know, the company said, we don't even know why this works, but you should buy it. It's great marketing, honestly. So this has been the topic of intense debate.

on Wiffle Ball Chat Rooms Online. The question being, how do the holes impact the ball's trajectory? This is clearly what the Internet is for. Yes, to air the topics of our day. So the thing is, there's this whole hot rod culture of modifying wiffle balls where people scuff or scratch up the plastic or knife the ball, modifying the size and shape of the holes. Wow, wow, wow.

Yeah, there's tutorial videos like these where we, see Kyle Schultz, a founding member of Major League Wiffleball, plop a Wiffleball smooth side down on his driveway. I make sure to get every... Wait, is there a major league Wiffleball league? Oh, Sophia, you have no... Are you just going to gloss over that? There's a major league for Wiffleball? You have no idea. Play the tape. I make sure to get every single part of the ball scuffed. What this does is

makes for better control. The ball will move more predictable as opposed to where it's unscuffed, and that's what we really want for our pitchers in this league. Honestly, if you ain't cheating, you ain't trying, Quang. But it's not cheating. It's a part of wiffle ball culture. Sure, okay. No one had really scientifically researched how the holes and any subsequent modifications

affect the ball until Jen Sturrowd Rossman came along. It was a whole new mystery for me to unravel and explore. So, in the early aughts, she and her students began running experiments. using the wind tunnel on the Lafayette College campus. They skewered wiffle balls to hold them in place at different angles and manipulated airspeed and spin rate to measure the subsequent forces on the ball. I am so jealous of this class. I had zero wind tunnels in my education.

Right? And the research paper that earned Jen this reputation as a foremost scientist of wiffleball aerodynamics came out in 2007 in the American Journal of Physics. So like 60 years after the Wifflebone. ball was made. Yes, it took a while, but Jen zeroed in on what was happening in the air that went through the holes and got trapped inside the ball, which she and her co-author, Andrew Rao, found a way to measure. And so we put something called a hot wire anemometer inside the ball as well. So it's in the wind tunnel and now we're measuring what's happening over it on it and inside of it. Yeah, yeah, sure.

No, physics stuff. Way to stick with it, Sophia. Okay. So, so. This air, inside the ball, created what she called a trapped vortex effect. Yep, I'm familiar. Basically, air recirculating and creating vortices that act on the ball from the inside. And her research, it not only showed that these vortices exist, but how their effect on the ball was driven by, one, the speed at which the ball was thrown, and two, the orientation of the ball when it was pitched. And so you could see that as the speed of the ball changed, the sort of battle, between outside effects and inside effects was shifting.

A battle like between the air moving outside the ball and inside the ball? Exactly. I'm nailing this. And with computer modeling, Jen and Andrew showed in detail how that battle plays out. And whether external or internal airflow has a greater effect on the ultimate trajectory of the ball. Okay. Give me like an example. Sure. Well, if you throw the ball at a certain angle and at a fast enough speed,

that internal airflow can actually cause the ball to curve away from the starting position of the holes, resulting in you throwing a sinker. Oh, like that annoying pitch where the ball drops right before it gets to you and it's tough to hit? Yes. Scuffing changes the flight paths of wiffle balls entirely. People who do that are basically amateur physicists experimenting with airflow. Okay. So basically the speed and the angle of the throw determine how the battle of the air inside and outside the ball plays out. And scuffing it up plays a role too. Yes. And Jen, by the way, she loves the DIY culture of souping up wiffle balls. For years, players have sent her their scuffed up wiffle balls. The first one, she remembers very clearly, it came wrapped in like lunch bag paper. And hand labeled on it was Professor Rossman. And inside there was just a note with this ball. And very small little scrap of paper, the note said, see if you can figure this one out.

I feel like that's a weird science ransom note. You know what I mean? Sure. Your mind goes to really weird places. But yes, she'll run these donated wiffle balls through her wind tunnel. And she and her students, they're actually now putting together a kind of atlas of scuffing and knifing patterns and their corresponding aerodynamic performance. For her, the wiffle ball, it's the perfect way to blend formal education with some fun

experimentation. Sometimes science gets taught as if it's like this monolithic body of knowledge that was inscribed in stone. And we forget to tell the stories of, no, people made this knowledge. And they did so by stumbling around and trying things and having the wrong idea and learning from that over and over again. And the more human you can make it, the more it's possible for any student, I think, to see themselves as potentially a doer of science. Quang, you really taught me some new things today, which, to be fair, is very easy when it comes to physics. But here's the

thing. We're all social distancing right now. So you and I, we're not wiffleballing anytime soon. No, it's probably best to play sports with people in your household, right? Who you are already sheltering at home with. I would check your local and state regulations, too, about park access. And if you have a backyard, obviously, that's your kingdom. You can do whatever you want there. And if you do want to toss a ball around, NPR sports correspondent Tom Goldman suggests you wash your hands before and after you play and polish that wiffle ball or whatever sport projectile you're using with an antibacterial wipe. But getting outside in a safe way and having fun, it's a really good thing to do at a time like this.

All right, Emily Kwong. Thank you for this little moment of wiffleball joy. Anytime, Maddie. Anytime. This episode was honestly produced somehow by Rebecca Ramirez, edited by Viet Le and fact-checked by Emily Vaughn. I'm Maddie Safaya. And I'm Emily Kwong. We'll see you back tomorrow with more shortwave from NPR.