The Science of Swing

The batter steps into a slightly inside fastball in the bottom of the ninth, with his team behind two runs and two runners on base. After hearing the crack of the bat, everyone immediately knows the result: It’s a home run.

Fans may barely think about it, but between the release of the pitch and the sight of the ball leaving the field, science takes hold.

As the Red Sox head back to Fenway Park and Boston University’s softball team takes to the field, science plays an enormous role at the plate, on the field and behind the scenes.

HAVING A BALL

The Diamondbacks’ Randy Johnson can throw it at speeds of more than 100 mph. The Red Sox’ Tim Wakefield can make it unpredictably dip and dive. But before any pitcher can throw a baseball, science reveals how the spheres are created.

James Sherwood, the director of baseball research at the University of Massachusetts at Lowell, knows baseballs so well that Major League Baseball hired him to investigate the “juiced ball” controversy that followed a record number of home runs in spring 2000.

Sherwood and a team of scientists traveled to baseball factories in Costa Rica and Ludlow, Vt. to study the intricate processes that take place during the creation of baseballs.

A baseball’s center has three major components, Sherwood said. The ball’s core, which consists of rubber mixed with cork particles, is surrounded by a layer of black rubber and a layer of red rubber.

This part of the ball must rebound from a hard surface within strict guidelines.

The ratio of the differences in the ball’s velocity before and after the collision, which measures its bounce, must fall between .544 and .578, he said. This is called the coefficient of restitution.

Machines then roll a four-ply gray yarn around the three layers of rubber before adding a white wool thread and a three-ply yarn, Sherwood said. The machines then add a cotton thread to the rubber and yarn, and workers glue on the leather cover and hand-stitch the trademark red yarn around the ball.

Sherwood and his team ripped apart baseballs from the Costa Rican factory in their investigation but found every ball met Major League specifications, putting an end to the “juiced ball” debate.

“It was just the hitters were getting better,” Sherwood said. Today, he continues to check baseballs for quality control for Major League Baseball.

CARRY A SMALL STICK

Another crucial piece of equipment, bats, must also meet strict specifications before ending up in sluggers’ hands.

“Ballplayers are very specific about their needs,” said Anne Jewell, director of the Louisville Slugger Museum in Louisville, Ky. “Each bat is custom made to order with a certain weight, length, handle, knob and other characteristics. If a bat is off just a little bit, the player can tell.”

Most baseball bats are made from either white ash or maple wood, and the best wood comes from forests on the border of Pennsylvania and New York because of the damp, cool climate, Jewell said. This is where most Louisville Slugger bats – manufactured since 1884 – originate, she said.

While traditional white ash is the choice of many players, Jewell said maple bats are becoming popular among top Major Leaguers.

“Ash has been the most predominantly used wood for many years because of its weight, strength and resistance to shock,” Jewell said. “Maple is the choice among a growing number of players. It is harder than ash and a little heavier with less elasticity.”

Regardless of what their bats are made of, many players often find themselves awing fans by shattering a bat after a particularly hard swing.

Because maple bats “shock,” or vibrate heavily, they tend to break more easily than ash bats, Jewell said.

Daniel Russell, an associate professor of applied physics at Kettering University in Flint, Mich., said broken bats can also result from a player “thinning” a bat – slightly shaving off some of the wood.

“The newer bats are really thin,” Russell said. “The only way you can make a bat lighter is by cupping the end, or gouging out a bunch of wood like a teacup. Thinning makes it more likely to break.”

Modern bats are also much lighter than in the days of Babe Ruth or even Mickey Mantle. Jewell said most players in the early 20th century believed the ball would go farther off of a heavier bat.

While Ruth used a 40-ounce bat to hit 60 home runs in 1927, Jewell said today’s bats only average about 32 ounces.

IF IT AIN’T

GOT THAT SWING

But how does it all come together?

The connection of a light rubber ball and a heavy wooden stick is as basic as bouncing off a trampoline, Russell said, an action he calls the “trampoline effect.”

“Basically I tap a bat with a hammer, measuring the force with an accelerator, and I measure frequencies and shapes of vibrations,” Russell said. “On a wood bat the ball comes in, hits the bat and the bat doesn’t give … it’s solid.”

While wooden bats force the ball to compress without a trampoline effect, he said aluminum bats have much more give, which allows the ball to travel farther.

Russell said an aluminum barrel compresses due to the trampoline effect, which takes responsibility off the ball to compress. Since the ball does not waste energy compressing, it rebounds off the bat faster.

“Aluminum will outperform wood, no question,” he said.

Still, Major League Baseball only allows wooden bats, so players have learned the best place on a bat to hit a ball. However, Russell said the sweet spot can be defined 15 different ways.

“If you hit it at the sweet spot – about seven inches from the end of barrel – the bat doesn’t vibrate,” Russell said. “When you hit at the sweet spot, it’s going to feel like a good hit.”

The vibration many batters feel occurs when the ball is hit away from the middle of the bat, and Russell said it’s strongest when a ball strikes near the end of the barrel.

“There’s a two- to three-inch range where it feels good, and that’s about four to seven inches from the barrel at the end of the bat,” Russell said.

THE CORKING QUESTION

But sometimes a broken bat can have consequences players never imagined.

Last June, perennial Chicago Cubs standout Sammy Sosa broke a bat, revealing cork he had manually drilled into the bat. Corking – drilling into the bat and filling it with an external substance – is illegal.

Because Sosa has hit more than 50 home runs in multiple seasons, a national controversy caused experts to question corking’s effects.

With a team of scientists, Russell took three baseball bats and hollowed out two of them. He filled one of the bats with cork and the other with super-balls – small rubber balls Chicago White Sox player Norm Cash used inside his bat in 1972 and 1973.

Russell’s team then swung the two corked bats and the un-corked bat at 150 mph fastballs from a pitching machine. They measured the speeds of the batted balls and came to an interesting conclusion.

“Corking made no difference at all,” Russell said. The slightly quicker speed of the lighter, corked bat “may give you an extra six feet of ball travel before you can commit to swinging, but to most players that’s barely noticeable.”

Russell said he believes corking a bat only gives a player a psychological advantage.

“If you know it’s a corked bat, you may be inclined to swing better,” he said. “I thought it may be fun to take a collection of bats -some corked, some not – and have guys play and see if they can tell the difference.”

Russell noted that Cash won the American League batting championship in 1972, but in 1973 – with his bat still corked – his hitting slumped dramatically.

While corking is one of baseball’s most scientific issues of the last 10 years, pure superstition may be just as important as science.

“Baseball is a very superstitious sport,” Russell said. “[Red Sox shortstop] Nomar Garciaparra steps up to the plate with his little ritual doing and undoing his batting gloves. As long as they keep their rituals, they feel good.”