Effects of angle and velocity of incidence, surface, and surface condition on the rebound behavior of a baseball

Vita.The purpose of this study was to determine and compare the effects of surface (SRF), angle (ANG) and velocity of incidence (VEL), and surface condition (SFC) on the angle of rebound (AR), horizontal velocity of rebound (HVR), and velocity of rebound (VR) of rebounding baseballs. A Locam high-speed camera operating at 200 fps was employed to record on film the incidence and rebound trajectories of baseballs colliding with three different surfaces under wet and dry conditions. The three surfaces consisted of an artificial turf, an infield dirt surface, and an infield grass surface. Thirty-six Rawlings RO-R® baseballs were projected from an ATEC pitching machine at three different angles of incidence and at three different velocities of incidence onto the three surfaces under both wet and dry conditions. A total of 162 observations were recorded on film. Three observations were filmed for each SRF x ANG x VEL x SFC combination. Film analysis was performed through use of a Vanguard Motion Analyzer. Kinematic quantities determined from Vanguard X and Y coordinates included ANG, VEL, AR, HVR, and VR. For each dependent variable (AR, HVR, and VR), a 3 x 3 x 3 x 2 ANOVA with repeated measures on the last three factors was utilized to test for significant differences at an adjusted (Bonferroni) alpha level of .0167. Results of the ANOVA omnibus tests revealed a three factor interaction (SRF x ANG x SFC) for AR, four two-factor interactions (SRF x ANG, SRF x VEL, ANG x VEL, and ANG x SFC) for HVR, and a four factor interaction (SRF x ANG x VEL x SFC) for VR. Simple main effects analyses were used to identify differences within the interaction profiles. When appropriate, an SNK procedure was utilized to identify differences within the levels for significant simple main effects profiles. Results of this study indicate a number of factors in combination influence the rebound behavior of baseballs. Significant main effects for any single factor were not directly interpretable due to significant interactions