Title: Baseball Aerodynamics: What do we know and how do we know it Alan M' Nathan University of Illinois a
1Baseball 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
2IntroductionForces on a Spinning Baseball in
Flight
- gravity physics 101
- drag wind resistance
- lift Magnus force on spinning baseball
3IntroductionForces on a Spinning Baseball in
Flight
- drag is opposite to direction of motion
- lift is in direction that leading edge is
turning
4Effect of Drag and Lift on Trajectories
- drag effect is huge
- lift effect is smaller but significant
5Some 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
6Some 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.
7Some Effects of Lift
Balls hit to left/right curve toward foul pole
8Some Effects of Lift
Tricky popups with lots of backspin
9Lets 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
10Experiment 1 Tracking Trajectory(UC/Davis
Illinois)
11Motion Capture Geometry
12- 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
13Typical Data
14Results for Lift Coefficient CL
FL 1/2?ACLv2 Sr?/v 100 mph, 2000
rpm ?S0.17
15Results for Drag Coefficient CD
FD 1/2?ACDv2
Conclusion Major disagreements for v 70-100
mph
16Experiment 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
17Sportvision Data
batters view
225o
Backspin up and in to RHH
18Sportvision Data
batters view
135o
Backspin up and away to RHH
19Sportvision Data
game pitches
warmup
20 Synthesis of Results
21 Synthesis of Results
Uncertainty in drag ? 50 ft!
22Summary
- 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?