The Flight of a Baseball Alan M Nathan

The Flight of a Baseball Alan M. Nathan, University of Illinois a-nathan@illinois. edu http: //go. illinois. edu/physicsofbaseball • Introduction • PITCHf/x and HITf/x • Using baseball to learn about physics • Using physics to learn about baseball -how pitchers do what they do -how batters do what they do APS/DFD, Nov. 2009 1

Forces on a Spinning Baseball in Flight FM • Drag slows ball down FD • Magnus + mg deflects ball from straight line APS/DFD, Nov. 2009 mg 2

Real vs. “Physics 101” Trajectory: Effect of Drag and Magnus APS/DFD, Nov. 2009 3

PITCHf/x and HITf/x • Two video cameras @60 fps – “high home” and “high first” – tracks every pitch in every MLB ballpark • all data publicly available on web! – tracks initial trajectory of batted ball • Used for analysis, TV broadcasts, MLB Gameday, etc. Image, courtesy of Sportvision APS/DFD, Nov. 2009 4

So what good is a physicist in all this? • Minimal parametrization of the trajectory – Constant acceleration works very well for pitched ball – Batted balls: ? ? ? • Determining Magnus acceleration – “spin movement” important for studying pitching • Dealing with noisy data, miscalibrations, etc. • Keeping everyone honest – Measurements have uncertainties! APS/DFD, Nov. 2009 5

Baseball Analysis: Using PITCHf/x to discover how pitchers do what they do “Hitting is timing. Pitching is upsetting timing. ” APS/DFD, Nov. 2009 6

Ex 1: Mariano Rivera: Why is he so good? ? Home Runs home plate Three Reasons: Location, APS/DFD, Location Nov. 2009 7

Ex 2: “Late Break”: Truth or Myth Mariano Rivera’s Cut Fastball View from above: actual trajectory -------linear extrapolation - - APS/DFD, Nov. 2009 8

Ex 2 a: What makes an effective slider Josh Kalk, THT, 5/22/08 side view APS/DFD, Nov. 2009 This slider is very effective since it looks like a fastball for over half the trajectory, then seems to drop at the last minute (“late break”). 9

Ex 3: A Pitcher’s Repertoire LHP Jon Lester, August 2007 4 -seam fastball >90 mph 80 -90 mph <80 mph slider 2 -seam fastball curveball Catcher’s View APS/DFD, Nov. 2009 10

Ex 4 Jon Lester vs. Brandon Webb 15 inches Brandon Webb is a “sinkerball” pitcher: Almost no rise on APS/DFD, Nov. 2009 his fastball 11

Ex 5 The Knuckleball Tim Wakefield is a knuckleball pitcher: Chaotic Movement APS/DFD, Nov. 2009 12

Studies of Batted Balls • HITf/x v 0, , • Hittracker (Greg Rybarczyk) – Landing point – Flight time • Together these constrain the full trajectory APS/DFD, Nov. 2009 13

Hitting a Long Fly Ball R vs. v 0 R vs. 0 USEFUL BENCHMARK 400 ft @ 103 mph ~5 ft per mph APS/DFD, Nov. 2009 peaks @ 25 o-35 o 14

What Constitutes a Well-Hit Ball? w/o home runs BABIP home runs V 0>90 HR APS/DFD, Nov. 2009 15

Putting Spin on Batted Balls • undercutting/overcutting backspin/topspin – upward/downward Magnus force • In front or behind sidespin – sideways Magnus force friction v normal force friction APS/DFD, Nov. 2009 16

Some Familiar Effects Due to Spin • Balls hit to left/right break toward foul line APS/DFD, Nov. 2009 17

Extract sidespin vs. from trajectory LF CF RF LHH RF LF RF break to right RHH break to left • Balls break toward foul pole • Break increases with angle • Ball hit to CF slices LHH/RHH asymmetry. APS/DFD, Nov. 2009 Tilt in bat 18

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Some Familiar Effects Due to Spin • Balls hit to left/right break toward foul line • Topspin makes line drives nose-dive • Backspin keeps fly ball in air longer • Tricky popups to infield ? ? ? APS/DFD, Nov. 2009 20

Paradoxical Popups APS/DFD, Nov. 2009 for bounce of ball Watch for fielder’s confusion and 21

HITf/x+hittracker Analysis: The “carry” of a fly ball (379, 20, 5. 2) • Motivation: does the ball carry especially well in the new Yankee Stadium? • “carry” ≡ (actual distance)/(vacuum distance) for same initial conditions APS/DFD, Nov. 2009 22

HITf/x + hittracker Analysis: 4354 HR from 2009 Denver Cleveland APS/DFD, Nov. 2009 Yankee Stadium 23

Summary We are on the verge of major breakthrough on our ability to track baseballs and determine the aerodynamic effects The new tools I have discussed are already revolutionizing baseball analysis And the tools are getting better…. So, fun times ahead for me… …shown here doing experimental baseball physics APS/DFD, Nov. 2009 24