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Physics 199BB The Physics of Baseball

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Physics 199BB The Physics of Baseball

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    1. Week 5 1 Physics 199BB The Physics of Baseball Fall 2007 Freshman Discovery Course Alan M. Nathan 403 Loomis 333-0965 a-nathan@uiuc.edu Week 5

    2. Week 5 2 Forces on a Baseball in Flight Gravity Already discussed Drag (“air resistance”) Force Already discussed Magnus Force Already discussed

    3. Week 5 3 Review: Here are the formulas FMx = FM {sin (?)vz/v-cos(?)vy/v} FMy = FM cos (?)vx/v FMz = -FM sin(?)vx/v aMx=2.09x10-6 CM?g {sin(?)vz-cos(?)vy} aMy=2.09x10-6 CM?gcos(?)vx aMz=-2.09x10-6 CM?gsin(?)vx

    4. Week 5 4 The PITCHf/x Tracking System MLB Gameday

    5. Week 5 5 How Does PITCHf/x Work? Two video cameras track baseball in 1/60-sec intervals usually “high home” and “high first” third CF camera used establises ht. of strike zone for each batter Pattern-recognition software to identify “blobs” Camera calibration to convert pixels to (x,y,z) 9-parameter fit to trajectory constant acceleration for x(t),y(t),z(t) Use fit to calculate lots of stuff

    6. Week 5 6 Example: Bond’s 756th home run

    7. Week 5 7 What kind of “stuff”? Pitch speed at release Pitch speed at home plate (~10% less) Location of pitch as it crosses home plate “break” of pitch—deviation from straight-line trajectory Release point of pitch ball Initial velocity direction

    8. Week 5 8 And the good news is…. …all these data are freely available online! to learn how to do it, see http://webusers.npl.uiuc.edu/~a-nathan/pob/pitchtracker.html Example: Jon Lester (Red Sox) vs. Seattle, Aug. 3, 2007

    9. Week 5 9 “movement” vs. “break”

    10. Week 5 10 pfx_x and pfx_z (“movement”) Deviation of trajectory due to spin of baseball Calculated by setting ax=0 (no sideways acceleration) az = -g (vertical acceleration only from gravity) calculate location of ball as it crosses home plate compare with actual location pfx_x, pfx_z = actual-calculated pfx=sqrt(pfx_x2 + pfx_z2)—reported on Gameday screen

    11. Week 5 11 “break” vs. “movement” Fastball with lots of backspin has lots of “movement” but little “break” Any ball dropping more than a fastball has more vertical “break” Baseball people prefer “break” to “movement” Physicists prefer “movement”

    12. Week 5 12

    13. Week 5 13 Using PITCHf/x to obtain drag and Magnus forces

    14. Week 5 14 Pitch Classification

    15. Week 5 15 Pitch Classification

    16. Week 5 16 Pitch Classification

    17. Week 5 17 New Topic: Discussion of the “Chemical Bonds” Paper

    18. Week 5 18 Topics for Next Time (Adair, Chapter 4) Knuckleball and scuff balls Gyroballs

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