Physics 199BB The Physics of Baseball

1
Physics 199BBThe Physics of Baseball

• Fall 2007 Freshman Discovery Course
• Alan M. Nathan
• 403 Loomis
• 333-0965
• a-nathan_at_uiuc.edu
• Week 6

2
Miscellaneous Topics from Adair,Chapters 2 and 4

• Chapter 2 The Flight of the Baseball
• Chapter 4 Pitching

3
Some Topics I Will Cover

• Effect of wind
• Effect of altitude and temperature
• Estimating home run distances
• Keeping the batter off balanced
• The knuckleball

4
Effect of Wind

• on a batted ball see Wind.xls
• example 100 mph, 30 deg, 2000 rpm backspin
• distance with no wind 395 ft
• distance with 10 mph 375/413 ft
• hence, average effect is about 2 ft for each 10
  mph
• note headwind increases drag but also increases
  Magnus
• on a pitched ball lets estimate

5
Effect of wind on pitched ball

• Headwind or tailwind
• drag vf ? 0.9v0
• with wind (vf /- vw) 0.9(v0 /- vw)
• for headwind/tailwind
• vf 0.9v0 -/ 0.1vw for headwind/tailwind
• example 10 mph wind
• 1 mph effect on vf
• ½ mph effect on average velocity
• ball arrives at plate 4 inches (later/sooner)
• See Adair, p. 66
• not very significant

6
Effect of wind on pitched ball

• Sidewind (10 mph)
• sideward component to drag
• if head-on drag ? weight of ball
• sideways drag is 1/9 of weight of ball
• sideways break is 1/9 drop due to gravity
• 3 ft/9 0.33 ft ? 4 inches
• see Adair, p. 66
• this could be significant

10 mph
90 mph
7
Effect of wind on pitched ball

• Effect of headwind on curveball
• Magnus force proportional to v
• v is larger with a headwind
• therefore, greater break with headwind
• estimate
• v75 mph, vw10 mph
• Magnus force larger by 85/751.13
• Break is 13 greater (2-3 inches)
• well known to discus throwers!

8
(No Transcript)
9
Effect of Altitude and Temperature

• FD ½CD?Av2
• FM ½CM?AR?v

• air density ? reduced by 4 per 1000 ft
• elevation
• 10o F change in temperature changes ? by 2
• changing pressure affects both drag and Magnus

see pressure.xls
10
PITCHf/x Data Toronto vs. Denver
11
How Far Did That Home Run Travel?
-time of flight can remove the ambiguity -see
HomeRunDistance.xls
12
Hitting is timing. Pitching is upsetting
timing. Effect of varying the speed
13
Hitting is timing. Pitching is upsetting
timing. Effect of varying the spin
14
What about the knuckleball?

• Surface roughness induces turbulant air flow
• Turbulant airflow reduces drag
• thats why golf balls have dimples
• Stitches on baseball reduce drag
• for spinning ball, drag is symmetric
• for non-spinning ball, drag can be asymmetric
• for slowly spinning ball, force can change
  directions
• Such force responsible for the swing of a
  cricket ball
• Scuff ball can be effective too

15
(No Transcript)
16
(No Transcript)
17
(No Transcript)