Baseball Aerodynamics: What do we know and how do we know it Alan M' Nathan University of Illinois a

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Baseball Aerodynamics What do we know and how
do we know it?Alan M. Nathan University of
Illinois at Urbana-Champaigna-nathan_at_uiuc.eduww
w.npl.uiuc.edu/a-nathan/pob

• Introduction
• Qualitative Effects of Drag and Lift
• Measurements of Drag and Lift
• Summary

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IntroductionForces on a Spinning Baseball in
Flight

• gravity physics 101
• drag wind resistance
• lift Magnus force on spinning baseball

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IntroductionForces on a Spinning Baseball in
Flight

• drag is opposite to direction of motion
• lift is in direction that leading edge is
  turning

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Effect of Drag and Lift on Trajectories

• drag effect is huge
• lift effect is smaller but significant

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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

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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.

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Some Effects of Lift
Balls hit to left/right curve toward foul pole
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Some Effects of Lift
Tricky popups with lots of backspin
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Lets Get QuantitativeMeasurements 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

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Experiment 1 Tracking Trajectory(UC/Davis
Illinois)
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Motion Capture Geometry
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• 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

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Typical Data
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Results for Lift Coefficient CL
FL 1/2?ACLv2 Sr?/v 100 mph, 2000
rpm ?S0.17
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Results for Drag Coefficient CD
FD 1/2?ACDv2
Conclusion Major disagreements for v 70-100
mph
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Experiment 2 SportvisionA 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
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Sportvision Data
batters view
225o
Backspin up and in to RHH
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Sportvision Data
batters view
135o
Backspin up and away to RHH
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Sportvision Data
game pitches
warmup
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Synthesis of Results
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Synthesis of Results
Uncertainty in drag ? 50 ft!
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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 vgt100 mph
• Dependence of drag/lift on seam orientation?
• Is the spin constant?