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## PowerPoint Slideshow about 'Introduction: Forces on a Spinning Baseball in Flight' - mike_john

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Presentation Transcript

FM

Fd

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Introduction:Forces on a Spinning Baseball in Flight- gravity: “physics 101”
- drag: “wind resistance”
- lift: Magnus force on spinning baseball

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Introduction:Forces on a Spinning Baseball in Flight- drag is opposite to direction of motion
- “lift” is in direction that leading edge is turning

Effect of Drag and Lift on Trajectories

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

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

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.

Some Effects of Lift

Balls hit to left/right curve toward foul pole

Some Effects of Lift

Tricky popups with lots of backspin

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

Motion Capture System

ATEC 2-wheel pitching machine

Baseball with reflecting dot

Experiment #1: Tracking Trajectory(UC/Davis; Illinois)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

Results for Lift Coefficient CL

Conclusion: data qualitatively consistent (~20%)

FL= 1/2ACLv2

S=r/v

100 mph, 2000 rpm

S=0.17

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

Synthesis of Results

Uncertainty in drag 50 ft!

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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