A Physicists Approach Alan M Nathan University of Illinois anathanillinoisedu pobguy baseballphysicsillinoisedu From Ben Lindbergh The Ringer 2 Possible Reasons for Surge ID: 638037
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Deconstructing the Home Run Surge:A Physicist’s Approach
Alan M. Nathan, University of Illinois a-nathan@illinois.edu @pobguy baseball.physics.illinois.edu
From Ben Lindbergh, The RingerSlide2
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Possible Reasons for Surge
Increased COR of baseballBall carries betterBatters alter swing Slide3
1. Increased COR (“bounciness”)Increased CORhigher exit speeds-> more HRI discussed this topic in my 2016 Saberseminar presentationSee Lindbergh/MGL Ringer article, May 2017I won’t further discuss here 3Slide4
lift
gravity
drag
2. Better “carry”
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Physics 101 (vacuum!):
Fly ball distance
completely determined by EV,
LA
Real life: drag and
lift…
Properties of air
Properties of ball
Ball carries
better when travels farther for identical initial conditions
i.e., EV
, LA, direction, spin, spin axisSlide5
Reasons for different carryAtmospheric conditions changedTemperature, altitude, wind, …Can control for this w/covered stadiumProperties of ball changedDrag or lift coefficients CD, CLSize of ball AWant to control the first to study the second5Slide6
CD Variation from PITCHf/x(controlled for atmospheric effects)6Lots of variation of drag coefficientSlide7
MMP Experiment(Saberseminar 2015)7EV=96 mphLA=280
80-ft spread!Slide8
Physics InterludeCD is largest on smooth ball (“laminar flow”)CD is smaller on rough surface (“turbulant flow”)Plumbing: corregated pipes improve flowGolf: dimples reduce dragBaseball: seams reduce dragBut….But if seams too high, CD increases
Where is crossover?8Slide9
Drag and Seam Height9NCAAMiLBMLB
EV=96 mphLA=28
0Slide10
Rob Arthur’s AnalysisUse PITCHf/x or Trackman pitch-tracking data to extract average CD valuesLook at correlation with HR/FB10Slide11
11Slide12
My Approach12Use Trackman batted-ball trajectories from TBAatmospheric effects constantUse 2016-b data to fix model for CD and CL “training” data 5 parameters for dependence on spin, speedWith fixed model & given initial conditions, calculate trajectory for 2015-E, 2015-L, 2016-a, 2017-ECompare calculated with actual landing pointSpeed, angles, spin rate, spin axisSlide13
Fitting to Training Data13153 batted ballsEV>90 mph, LA=200-350
rms=2
ftSlide14
The Results: Actual-Calculated14~ 5 ftSlide15
Some CommentsThere is considerable ball-to-ball variation in CDOnly makes sense to compare averagesEach data set has 100-200 trajectoriesData shows ~5 ft increase from 2015-E to 2016, then constantEstimate: 5 ft~15% more HR15
~5
ftSlide16
Into the weeds….16CD = 0.02 (distance) ~8.5 ft
~25% more HR
sSlide17
ConclusionThere is evidence suggesting some (~15%) of increase in HR between 2015 and 2016 is due to reduced dragReminder: atmospheric effects held constant at TBABetter carry must be due to properties of ballData are consistent with no change in drag from 2016 to 201717Slide18
AfterthoughtOriginal motivation for this analysis was to build a new 3D Trajectory CalculatorSpreadsheet to calculate trajectories, given EV,LA,SA,spin rate,spin axisBeta version is readybaseball.physics.illinois.edu/TrajectoryCalculator-new-3D.xlsxFeedback welcome18Slide19
3. Batters alter swing19Slide20
wOBA vs. EV-LA(actually, wOBAcon)20Launch Angle (deg
)
Exit Speed (mph)Slide21
Possible Hitting StrategiesTo get 1Bhit hard and 100-150To hit xBHhit hard and 250-300To minimize timing errorsswing “level”
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Question: How does batter adjust swing to optimize outcome?Slide22
Issues for swinging the bat(*things I will consider)*TimingGetting bat in right place at right timeSwing speedHigh!*Aim—where on bat impact occursAlong axis of bat (“sweet spot”)*Perpendicular to axis of bat (“offset”)*Swing plane22Slide23
Ball-Bat Collision Model(2D version)23Batter controls: = swing plane (attack angle)E= offset (“aim”)~Max EV when =
CL
Physics Model: (,E)EV,LASlide24
Swing Plane + Offset EV+LA24
HR
1BSlide25
25Max wOBA:~240 swing plane
~1.1” offsetSlide26
Ex 1: Kris DaviswOBAcon=0.48826200
~20
0 swing planeSlide27
Ex 2: Ryan Zimmerman wOBAcon=0.3462770~100
swing planeSlide28
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“level”
uppercut
Timing &
Swing Plane
Suppose swing mistimed by ~±3
ms
, or ~±4”
“Level” swing: E does not change
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0
swing:
E
changes by ~
±0.8”
(!)
popup
weak grounderSlide29
29popupgrounder
Timing &
Swing Plane±0.8”Slide30
SummaryLA for max EV related to swing planeIn general, for given max EV, wOBA increases as swing plane increasesI have not done a complete statistical analysisWork in progress30Slide31
And finally….The beat goes on with the COR storySome evidence for reduced drag starting in 2016New Trajectory Calculator a by-productEV-LA a potentially useful toolMy view: The question of why the HR surge is still not fully answered31Slide32
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