Introduction: Forces on a Spinning Baseball in Flight

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# Introduction: Forces on a Spinning Baseball in Flight - PowerPoint PPT Presentation

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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Presentation Transcript
FM

Fd

mg

Introduction:Forces on a Spinning Baseball in Flight
• gravity: “physics 101”
• drag: “wind resistance”
• lift: Magnus force on spinning baseball
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
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)
~15 ft

Joe Hopkins

Motion Capture Geometry

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= 1/2ACLv2

S=r/v

100 mph, 2000 rpm

S=0.17

Results for Drag Coefficient CD

FD= 1/2ACDv2

Conclusion:

Major disagreements for v= 70-100 mph

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

Sportvision Data

batter’s view

225o

Backspin:

up and in to RHH

Sportvision Data

batter’s view

135o

Backspin:

up and away to RHH

Sportvision Data

game pitches

warmup

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?