Bat design and ball exit velocity in baseball: Implications for player safety
R.L. Nicholls* , B.C. Elliott & K. Miller
University of Western Australia
This study investigated the effect of bat design on linedrive speed. The selection of wood or metal materials promotes considerable design differences between bats. The greater density of aluminium alloys means the bat must be shaped as a hollow tube to maintain the same weight as a solid ash bat, whose mass is distributed throughout the implement, with a greater proportion of mass located in the hitting region (barrel). Resistance to angular acceleration is determined by the distribution of bat mass with respect to its axis of rotation. As a first class lever rotating about the hands against the resistance of the barrel weight, for a given torque the “end-heavy” wood bat will achieve less angular acceleration than a metal bat. Such a bat also requires greater impulse to produce a change in bat speed, resulting in decreased linear velocity of the barrel, thereby imparting less velocity to the ball (Noble, 1998; Hay; 1973).
Statement of the Problem
To develop effective standards for equipment and maximise player safety in baseball, the effect of bat design on ball exit velocity must be quantified. Metal bats are currently certified”“safe” before commercial sale using robotic swing testing. The purpose of this study was to quantify the effect of bat weight distribution on ball exit velocity from metal and wood bats swung by high-performance hitters.
Baseball bats: One metal bat and one wood bat were selected for analysis. Bat specifications are listed in Table 1 (expressed in both SI and empirical units as is traditional in baseball). Bats were selected as representative of the length and mass of bats used in high school and collegiate baseball. The metal bat was constructed from an alloy of heat-treated zinc, magnesium and aluminium. The wood bat was a solid northern white ash bat. Although sold as conforming to NCAA mass and length restrictions (which state the empirical length-to-weight differential must not exceed 3), the metal bat was approximately 30 g lighter than the certified weight. While the bats were virtually identical in length and similar in mass, the primary difference between the two bats was the location of the centre of mass (CM). The theoretical point around which the mass of the metal bat was distributed was located using a knife-edge balance technique (Hay, 1973), and was found to be approximately 5 cm closer to the handle than that of the wood bat.
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