The most stunning change in baseball bats in the past thirty years started in the 1970s, when bats made from tubes of aluminum began to appear. These tubes are machined to vary the wall thickness and the diameter, and produce bats that are light, strong, and hollow, as opposed to the solid wood.

"At first," says George Manning, "the aluminum bat was just a metal copy of a wooden bat. They were just more durable, so they were cheaper to use." But manufacturers and players soon discovered that there were other differences as well.

"Aluminum bats are quite different than wooden ones. They're much lighter - -more than five ounces. The barrels are bigger, and because they are lighter they can be swung faster than a wooden bat." In addition, the hardness and resilience of aluminum can result in much greater speeds when the ball comes off the bat. Major league baseball has required that its players use wooden bats, but the aluminum bat has come to dominate the lower levels of baseball, from Little League to the college game.

According to George Manning, the most significant difference between wooden and aluminum bats is that "with an aluminum bat, a phenomenon occurs called the 'trampoline effect.' The walls of the bat are thin enough that they deform or flex when the ball hits the bat. Some of the energy (of the collision) is transferred into the bat instead of the ball. That energy is almost totally elastic; it is given back, or bounces back, almost 100 percent. The energy absorbed when the ball is deformed is almost 75 percent lost to heat, and thus wasted as far as propelling the ball. Because of this trampoline effect, you can hit the ball somewhat faster, and somewhat farther. In fact, when the NCAA approved the use of aluminum bats in 1974, we started comparing statistics and found that the team batting averages went up about twenty points, and the home-run production about doubled."

The primary reason that wooden bats are required in the pros is due to this performance difference. "The pro leagues want to protect their historical records, and they want the performance of the game to be the result of human ability, rather than the technology of the bats," says Manning.

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