more on the grip ….5

Evidence #5: batted-ball speed for pivoted, swung (hand-held) and free bats

So far we’ve looked at a baseball bat experiment with very questionable results, an experiment which compared the vibrational frequencies of bats in different grip conditions, a simple experiment bouncing superballs off aluminum beams, and a computational model of the bat-ball collision. The last three studies agree in their predictions that grip conditions should have no affect on bat performance. However, is would be really nice if there was an experimental study players and realistic grip conditions. Fortunately such a study exists! In September 2004 I attended the 5th International Conference on Engineering of Sports and saw a very nice paper presented by Keith Koenig[10] and his colleagues from the University of Mississippi. Koenig’s laboratory is responsible for some of the early research which led to the development of the current ASTM test methods for comparing and measuring bat performance. They conducted the most comprehensive study I have seen so far regarding the effect of hand grip on baseball performance. They investigated three grip conditions. The first condition was free-free, with the bat simply balancing on two small posts about 9.5 inches from each end of the bat. Upon impact the bat was free to go flying away. The second grip condition was modeled after the clamped-pivot used for ASTM testing of bats. The bat was clamped in a fixture about two inches wide and centered at a location on the handle; two locations were chosen: 4.75″ and 5.75″ from the knob (ASTM standards use a location 6″ from the knob). The pivot was completely free to rotate about a fixed axis, allowing the bat to recoil and pivot about this axis, but not translate. The third condition was a hand-held grip in which four players (three experienced college and one semi-professional) swung the bat at a ball on a tee. In the first two cases (free and clamped/pivot) they fired balls from an air compression cannon towards a stationary bat, with incoming ball speeds varying between 50 and 110 mph. For the hand-held/swing-hit case they measured the bat swing speed at the impact location just prior to impact with a stationary ball. In all three cases care was taken to ensure that all impacts occured at the same location on the bat barrel, approximately 4-inches from the end of the barrel. This ensured that any differences in “batted-ball speed” would be due only to differences in grip conditions, not due to variations in impact locations.

The data in the figure below shows the combined results of all three tests (two pivots, free-free, and swing-hit). The fact that all of the data points appear to fall on a straight line indicates that grip conditions have absolutely no affect on batted-ball speed. If grip did affect performance, then we would expect to see three or four straight lines, one for each data set. Koenig’s results, however, show that there is no noticeable difference in the performance of a bat which is clamped in pivot, free-free, or gripped with the hands and swung by a player.

Koenig’s measured batted-ball speed as a function of pitched-ball speed (or bat swing speed) for a variety of grip conditions.

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