E N D
1. Week 5 1 Physics 199BBThe 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 SystemMLB 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: Bonds 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 pitchdeviation 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