Leveling the playing field
by Jeff Wolfe '03 | © Washington State University
In softball, success or failure happens when the ball meets the bat. The faster a batted ball travels, the greater the likelihood of a batter's success. Softball bat manufacturers are using technology to create bats that hit the ball harder than ever-but not everyone is pleased with the results.
Recent advances in softball bat performance raised concerns with the Amateur Softball Association (ASA) that softball bats generating high batted ball speeds were giving individuals an unfair advantage in competition and creating safety problems, says Lloyd Smith, an associate professor in the School of Mechanical and Materials Engineering at Washington State University.
Since 2000, the ASA, the national governing body of softball in the United States, has required softball bats to be ASA-certified before use in sanctioned play. Certification is based on the ball speed a softball bat can produce . However, the ASA discovered the bats they tested and certified were performing noticeably better in competition than their tests had predicted. In the summer of 2002, the ASA asked Smith, who had previously tested baseball bats, to figure out why the test was failing.
Smith started his search for an answer at an ASA championship tournament.
Using high-speed cameras and players with different skill levels, he discovered the weight of a bat does not affect its swing speed. Players swung a 28-ounce bat just as fast as a 26-ounce bat. Instead, Smith found swing speed to be dependent on a bat's mass moment of inertia (MOI).
"Imagine you're swinging a pole that has adjustable weights attached to it," says Smith. "If you move all the weight close to your hands, you will swing the pole much faster than if you moved all the weight to the end of the pole. The MOI describes this effect."
Currently, the ASA uses a test created by the American Society for Testing and Materials (ASTM) to certify bats. Smith says that one reason the ASA test doesn't accurately predict a bat's performance is that it uses a bat's weight instead of its MOI to determine batted ball speed.
Smith found other flaws in the test as well-for example, selection of where the ball hits the bat during testing. In the ASTM test, the ball strikes each tested bat in a location known as the center of percussion. It was believed that a bat's center of percussion corresponded with its "sweet spot," a location that provides the highest batted ball speed. Smith found, however, that while manipulating the distribution of weight within a bat (changing the bat's MOI) changes the location of the center of percussion, the location of the sweet spot remains the same. As a result, bats that show similar performance in current laboratory tests don't necessary perform at the same level in competition. "My job is to put the brakes on that," says Smith.
Smith has built a bat-testing lab at WSU to more accurately predict the performance of bats. The results obtained from preliminary testing are being used to recommend changes to ASA's current testing method. There are currently two labs certified to test softball bats for the ASA. WSU will likely have the third certified lab by the end of 2003, says Smith.
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