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Introduction: Forces on a Spinning Baseball in Flight

F M. F d. mg. Introduction: Forces on a Spinning Baseball in Flight. gravity: “physics 101” drag: “wind resistance” lift: Magnus force on spinning baseball. F M. F d. mg. Introduction: Forces on a Spinning Baseball in Flight. drag is opposite to direction of motion

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Introduction: Forces on a Spinning Baseball in Flight

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  1. FM Fd mg Introduction:Forces on a Spinning Baseball in Flight • gravity: “physics 101” • drag: “wind resistance” • lift: Magnus force on spinning baseball

  2. FM Fd mg Introduction:Forces on a Spinning Baseball in Flight • drag is opposite to direction of motion • “lift” is in direction that leading edge is turning

  3. Effect of Drag and Lift on Trajectories • drag effect is huge • lift effect is smaller but significant

  4. Some Effects of Drag • Reduced distance on fly ball • Reduction of pitched ball speed by ~10% • Asymmetric trajectory: • Total Distance  1.7 x distance at apex • Optimum home run angle ~350

  5. Some Effects of Lift • Backspin makes ball rise • “hop” of fastball • undercut balls: increased distance, reduced optimum angle of home run • Topspin makes ball drop • “12-6” curveball • topped balls nose-dive • Breaking pitches due to spin • Cutters, sliders, etc.

  6. Some Effects of Lift Balls hit to left/right curve toward foul pole

  7. Some Effects of Lift Tricky popups with lots of backspin

  8. Let’s Get Quantitative:Measurements of Drag and Lift • What do we know? • How do we know it? • How well do we know it? • Two types of experiments: • Wind tunnel • Measure forces directly • Video tracking of trajectory • “You can observe a lot by watching” • Infer forces from measured acceleration

  9. Motion Capture System ATEC 2-wheel pitching machine Baseball with reflecting dot Experiment #1: Tracking Trajectory(UC/Davis; Illinois)

  10. ~15 ft Joe Hopkins Motion Capture Geometry

  11. Motion Capture System: • 10 cameras • 700 frames/sec • 1/2000 shutter • very fancy software • www.motionanalysis.com • Pitching Machine: • project horizontally • 50-110 mph • 1500-4500 rpm

  12. Typical Data

  13. Results for Lift Coefficient CL Conclusion: data qualitatively consistent (~20%) FL= 1/2ACLv2 S=r/v 100 mph, 2000 rpm S=0.17

  14. Results for Drag Coefficient CD FD= 1/2ACDv2 Conclusion: Major disagreements for v= 70-100 mph

  15. Experiment #2: Sportvision—A Potential New Tool • Track pitched baseballs with 2 cameras • High-speed not necessary • Tracking of MLB game pitches • Used by ESPN for K-Zone • From trajectory, determine • lift,drag,spin axis • Spin rate not measured Thanks to Marv White, CTO, for providing a wealth of data

  16. Sportvision Data batter’s view 225o Backspin: up and in to RHH

  17. Sportvision Data batter’s view 135o Backspin: up and away to RHH

  18. Sportvision Data game pitches warmup

  19. Synthesis of Results

  20. Synthesis of Results Uncertainty in drag  50 ft!

  21. Summary • We have much empirical knowledge of lift and drag • …and some promising new tools for future research • Things we would like to know better: • Better data on drag • “drag crisis” • Spin-dependent drag? • Drag for v>100 mph • Dependence of drag/lift on seam orientation? • Is the spin constant?

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