July 2011, Week 1


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Mon, 4 Jul 2011 02:16:37 -0400
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The Physics of Cheating in Baseball 
Corked bats and juiced balls have long plagued baseball,
but do they really help a player's game? Four scientists
found surprising answers
By Christopher Solomon
June 24, 2011

Cheating in sports might be as old as the race between
the tortoise and the hare. But not all trickery actually
works, especially in baseball.

A corked bat can hit the ball farther, right? That's a
myth, say physicists studying the national pastime. And
can making a baseball moister really thwart a slugger
from putting one in the bleachers? Well, maybe-depending
on how hot it is outside.

To separate fact from fiction, four scientists from
three universities spent days firing baseballs at bats.
The results are published in "Corked Bats, Juiced Balls,
and Humidors: The Physics of Cheating in Baseball" in
the June issue of the American Journal of Physics.

To Cork or Not to Cork

In June 2003, Chicago Cubs slugger Sammy Sosa was caught
using an illegal corked bat-hardly the first time it's
happened in the Major Leagues. A corked bat is one in
which a cavity is drilled out of the barrel and filled
with a lightweight material such as cork.

It was scandalous, but does it work? That's the question
that intrigued Alan Nathan, a professor emeritus of
physics at the University of Illinois (and a die-hard
Red Sox fan). "There was some anecdotal information from
players that there's something like a `trampoline
effect' when the ball bounces off a corked bat," says
Nathan, one of the authors of the new study. So the
researchers hollowed out a bat, stuffed it with bits of
cork and fired a ball at the bat from a cannon. If
anything, the ball came off the corked bat with a slower
speed than off a normal bat. Less velocity means a
shorter hit. Their conclusion: the trampoline effect was

But there was another way corking might work: a corked
bat is a few ounces lighter than an unadulterated one,
and a lighter bat means a batter can swing faster, which
means he can generate more force and hit the ball
farther. Right?

Not quite, as it turns out.

A batter indeed can swing a lighter bat faster, but a
lighter bat has less inertia. So there's a trade-off,
says Lloyd Smith, an associate professor of engineering
at Washington State University and a co-author on the
paper. By once again firing a ball at a bat at WSU's
Sports Science Laboratory, the researchers found that a
heavier bat still hit the ball harder (and therefore
farther) than a lighter, corked bat. "Corking will not
help you hit the ball farther," says Smith.

"That's not to say that baseball players are dumb,"
Smith is quick to add. Players may have another reason
to cork their bats: to make the bats lighter so players
can, in baseball argot, "get around on a pitch" quicker,
allowing them to wait a split second longer before
swinging, which gives them more time to judge a ball's
path and to make adjustments during the swing. "So,
while corking may not allow a batter to hit the ball
farther, it may well allow a batter to hit the ball
solidly more often," the researchers write.

Smith summarizes it this way: "If your goal is to hit
more home runs, you should have a heavy bat. If your
goal is to have a higher batting average, you should
have a lighter bat."

Keith Koenig, a professor of aerospace engineering at
Mississippi State University and a fellow baseball
researcher, trusts the paper's results but cautions that
a bat-swinging machine can never fully predict what
might actually happen out on the diamond when real
batters swing bats. "If we allow corked bats in the
Major Leagues, would there be more home runs?" Koenig
muses. "That's the kind of question that can't be
answered just from lab tests."

Good Hitters-or a Juiced Baseball?

Every few years, during the month of April, Nathan says,
batters start hitting home runs and the cry goes up: The
baseball isn't what it used to be! It must be juiced!
(Why always in April? "Because in April there's not
enough data to be statistically significant.and people
start to speculate," Nathan says wryly.) The issue of
juiced balls surfaced again in 2000 when the first two
months of the season saw home runs hit at a notably
higher rate than the same period the previous year.

To test the speculation that something had changed with
the balls, the researchers compared the bounciness of
balls from 2004 with a box of unused balls from 1976 to
1980. They shot the balls at a steel plate or a wooden
bat at 60, 90, and 120 miles per hour and measured their
bounciness after a collision-what physicists call the
coefficient of restitution.

The result? "There was no evidence that there was any
difference in the coefficient of restitution of the
different balls," says Nathan. One caveat: the
scientists can't say that balls made in other years
aren't livelier.

How times change, though: these days we'd more likely
attribute a rash of home-run slugging to performance-
enhancing drugs, not the ball.

The Humidor: Not Just for Cigars Anymore

Coors Field, home of the Colorado Rockies in mile-high
Denver, is a pitcher's nightmare and a batter's nirvana.
The air is only 80 percent as dense as air at sea level,
and because there's less air resistance, balls fly
farther and pitches cannot curve as much. That means
more hits and more home runs. For the first seven
seasons at Coors Field, there were 3.2 home runs per
game, compared with 1.93 home runs at the Rockies' away

To try to discourage the mile-high bonanza, in 2002 the
Rockies started storing game balls in a humidor that
kept the balls at a constant 70 degrees Fahrenheit and
50 percent relative humidity instead of Denver's typical
30 percent humidity. The idea was that higher humidity
reduces the bounciness of the ball and slightly
increases its weight. Indeed, the average number of home
runs at Coors Field dropped 25 percent from 2002 through

But is the humidor really to thank (or blame) for the
decrease in home runs?

To test the theory, the authors placed several dozen
balls in conditions ranging from 11 percent to 97
percent relative humidity for weeks, and temperatures
from the 30s to nearly 100 degrees, then fired them
against metal cylinders that approximate bats. Again
measuring the coefficient of restitution, they found
that the colder and moister a ball was, the less bounce
it had. Translation: a ball hit on a hot dry day at an
Arizona ballpark will go noticeably farther than the
same ball hit on a frigid, foggy day at Boston's Fenway

As for Denver's Coors Field, the researchers calculate
that a humidity increase from 30 percent to 50 percent
would take 14 feet off a 380-foot fly ball-enough to
decrease the chances of a home run by 25 percent.

Not long ago, Nathan says, a reporter in Arizona
contacted him and told him that the Arizona Diamondbacks
were considering installing a humidor at their stadium,
too. Nathan did the math-this time starting at the
desert-air base-line of 20 percent relative humidity,
and conditioning balls to 50 percent relative humidity.
"That would be an even greater reduction in the number
of home runs, more like 37 percent," he says.

The Diamondbacks later put those plans on hold.
Everybody, it seems, likes at least a few homers between
their peanuts and Cracker Jack.


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