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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
FM

Fd

mg

Introduction:Forces on a Spinning Baseball in Flight
  • gravity: “physics 101”
  • drag: “wind resistance”
  • lift: Magnus force on spinning baseball
introduction forces on a spinning baseball in flight2
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
Effect of Drag and Lift on Trajectories
  • drag effect is huge
  • lift effect is smaller but significant
some effects of drag
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
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.
slide6
Some Effects of Lift

Balls hit to left/right curve toward foul pole

slide7
Some Effects of Lift

Tricky popups with lots of backspin

let s get quantitative measurements of drag and lift
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
experiment 1 tracking trajectory uc davis illinois
Motion Capture System

ATEC 2-wheel pitching machine

Baseball with reflecting dot

Experiment #1: Tracking Trajectory(UC/Davis; Illinois)
slide10
~15 ft

Joe Hopkins

Motion Capture Geometry

slide11
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 c l
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 c d
Results for Drag Coefficient CD

FD= 1/2ACDv2

Conclusion:

Major disagreements for v= 70-100 mph

experiment 2 sportvision a potential new tool
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
Sportvision Data

batter’s view

225o

Backspin:

up and in to RHH

sportvision data17
Sportvision Data

batter’s view

135o

Backspin:

up and away to RHH

sportvision data18
Sportvision Data

game pitches

warmup

synthesis of results20
Synthesis of Results

Uncertainty in drag  50 ft!

summary
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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