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Study of Spin Effects on Batted Baseball Trajectories

Explore the influence of spin on batted baseball trajectory, spin types, spin mechanisms, angular momentum, and final spin results. Discover insights on backspin, topspin, sidespin, and more.

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Study of Spin Effects on Batted Baseball Trajectories

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  1. Spin of a Batted Baseball Alan M. Nathana, Jonas Contakosa, Russ Kesmana, Biju Mathewb, Wes Lukashb aUniversity of Illinois at Urbana-Champaign bRawlings Sporting Goods

  2. Spin Affects Batted Ball Trajectories FM Familiar Effects: • Backspin keeps fly ball in air longer • greater distance • Topspin makes line drives nosedive • and leads to grounders with tricky bounces • Sidespin makes ball slice or hook toward foul pole • Backspin sometimes leads to “paradoxical popups” Fd mg

  3. 2000 fps

  4. normal force v friction Mechanism for Batted Ball Spin • Rolling: ex=0 • Sliding: ex<0 • Gripping: ex>0 • Superball: ex ~ 0.8 • “usual” assumption ex=0 • Low speed: ex~0.16

  5. Scattering Geometry Measure v1, v2, 1, 2,  Infer  • v1: 85-120 mph • 1: 0, 1000-3000 rpm

  6. Normalized Final Spin vs. Incident Angle to Normal () Incident backspin Incident backspin Incident backspin Zero incident spin Incident topspin Incident topspin Incident topspin Final spins depend on , ~independent of initial spin

  7. Final vs. Initial Tangential Speed Incident backspin Zero incident spin Incident topspin Slope = -ex • Data consistent with ex=0.3 (gripping) • Data inconsistent with ex=0 (rolling) • For >400, “gross slip” ensues

  8. Angular Momentum Conservation about Contact Point

  9. CoF and Ratio of Tangential to Normal Impulse Data consistent with very low CoF, ~0.15

  10. Summary of Conclusions • Final spin for given vTi nearly independent of initial spin • Data consistent with ex=0.30, implying considerable “overspin” • Data consistent with angular momentum conservation • Data consistent with very low CoF • puzzling!

  11. …and finally v0 = 96.6 mph,  = 30.5o, R = 374 ft b = 3300 rpm s = 425 rpm The Grip Doesn’t Matter!

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