Title: Baseball 101: A Primer on the Physics of Baseball Alan M. Nathan Saturday Physics Honors Lecture Oct
1- Baseball 101 A Primer on the Physics of
BaseballAlan M. NathanSaturday Physics Honors
LectureOctober 21, 2000
- Introduction
- When Ash Meets Cowhide
- The Aerodynamics of Baseball
- The Art of Pitching
- Summary
2REFERENCES
- The Physics of Baseball, Robert K. Adair (Harper
Collins, New York, 1990), ISBN 0-06-096461-8 - The Sporting Life, Davis and Stephens (Henry Holt
and Company, New York, 1997), ISBN 0-8050-4540-6 - http//www.exploratorium.edu/sports
- ME!
- a-nathan_at_uiuc.edu
- http//www.npl.uiuc.edu/a-nathan/pob
3Baseball and Physics Murderers Rows of 1927
4Hitting the Baseball
- ...the most difficult thing to do in sports
- --Ted Williams,
- Professor of Hitting
BA .344 SA .634 OBP .483 HR 521
all time leader
5Heres Why..
(Courtesy of Robert K. Adair)
6Trivia Timeout
- Rogers Hornsby is one of only two players to have
won the Triple Crown twice. Who is the other
player? - A) Hank Aaron
- B) Mickey Mantle
- C) Carl Yastrzemski
- D) Ted Williams
7When Ash Meets Cowhide
- A violent collision!
- forces large (gt8000 lbs!)
- time is short (lt1/1000 sec!)
- ball compresses, stops, expands
- kinetic energy ? potential energy
- lots of energy dissipated (friction)
- hands dont matter!
- GOAL maximize ball exit speed vf
- vf ? 105 mph ? x ? 400 ft ?x/?vf 4-5
ft/mph
What aspects of collision lead to large vf?
8Speed of Hit BallWhat does it depend on?
- The basic stuff (kinematics)
- speed of pitched ball
- speed of bat
- weight and weight distribution of bat
- The really interesting stuff (dynamics)
- bounciness of ball
- vibrations of bat
9What Determines Batted Ball Speed?
- How does batted ball speed depend on ...
- pitched ball speed?
- bat speed?
-
For typical collision on fat part of bat, ?0.2
1 ? 1.2
Conclusion Bat Speed Matters Much More!
Question What properties of ball/bat determine
??
10What Determines Batted Ball Speed?
11What Determines Batted Ball Speed?
12What is the Ideal Bat Weight?
Conclusion More data needed to determine
optimum bat weight.
13Trivia Timeout
- Who is this guy and what was his number?
Eddie Gaedel1/8
14The Coefficient of RestitutionEnergy
Dissipation in Ball
- COR measures bounciness of ball
- Final speed/Initial speed
- For baseball, COR? 0.5
- hf/hi 3/4
- 3/4 energy lost!
- Is the ball juiced?
-
15COR and the Juiced Ball Issue
- MLB COR 0.546 ? 0.032
- _at_ 58 mph on massive rigid surface
16Effect of Bat on CORTrampoline Effect
- Energy shared between ball and bat
- Wood Bat nearly incompressible
- 2 of energy stored in bat
- Efficiently restored to ball
- BPF 1
- Aluminum Bat
- 10-20 energy stored in bat
- Efficiently restored to ball
- Result trampoline effect
- BPF 1.1-1.2
- Ball flies off the bat!
Bat Performance Factor COReffective/COR
new NCAA rules ?lt.228
17Trivia Timeout
- Who is this guy?
- A) Joe Torre
- B) Don Zimmer
- C) Lou Skizas
- D) Roger Maris
18Effect of Bat on COR Bat Vibrations
- Collision excites bending vibrations in bat
- Ouch!! Thud!!
- Sometimes broken bat
- Energy lost ? lower COR
19Vibrational Modes of Bat Louisville Slugger R161
(33, 31 oz)
This can be measured!
20Putting it all together.
21Possible Physics Sweet Spots
- Center of Percussion (6)
- Node of lowest vibration (6)
- Maximum hit ball speed (5)
- Minimum total vibrations (5)
Question Where is batters sweet spot?
22Advantages of Aluminum
- Length and weight decoupled
- Can adjust shell thickness
- Fatter barrel, thinner handle
- Lighter
- Higher bat speed
- More of weight closer to hands
- Easier to swing
- Less rotational recoil
- More forgiving on inside pitches
- More compressible gt springier
- Trampoline effect, higher COR
- Stiffer for bending
- Less energy lost due to vibrations
23Trivia Timeout
- Who is the only player to steal five bases in one
game? - A) Ricky Henderson
- B) Lou Brock
- C) Tony Gwynn
- D) Ty Cobb
24Aerodynamics of a Baseball
- Forces on Moving Baseball
- No Spin
- Boundary layer separation
- DRAG!
- Grows with v2
- With Spin
- Ball deflects wake
- action/reaction ? Magnus force
- Force grows with rpm
- Force in direction front of ball is turning
25The Flight of the BallReal Baseball vs. Physics
101 Baseball
- Role of Drag
- Role of Spin
- Atmospheric conditions
- Temperature
- Humidity
- Altitude
- Air pressure
- Wind
26The Role of Friction
- Friction induces spin for oblique collisions
- Spin gt Magnus force
- Results
- Balls hit to left/right break toward foul line
- Backspin keeps fly ball in air longer
- Topspin gives tricky bounces in infield
- Pop fouls behind the plate curve back toward field
27The Home Run Swing
- Ball arrives on 100 downward trajectory
- Big Mac swings up at 250
- Ball takes off at 350
- The optimum home run angle!
28The Art of Pitching
- Don Larsen, 1956 World Series
- Last pitch of perfect game
- Hitting is timing. Pitching is upsetting
timing - ---Warren Spahn
- vary speeds
- manipulate air flow
- orient stitches
29Trivia Timeout
- Who is standing behind Don Larsen?
- A) Bobby Richardson
- B) Tony Kubek
- C) Billy Martin
- D) Yogi Berra
- Don Larsen, 1956 World Series
- Last pitch of perfect game
30How Much Does the Ball Break?
- Depends on
- Magnitude and direction of force
- Time over which force acts
- Calibration
- 90 mph fastball drops 3.5 due to gravity alone
- Ball reaches home plate in 0.45 seconds
- Half of deflection occurs in last 15
- Drag reduces fastball by about 8 mph
- Examples
- Hop of 90 mph fastball 4
- Break of 70 mph curveball 16
- slower
- force larger
31Example 1 Fastball
85-95 mph 1600 rpm (back) 12 revolutions 0.46
sec M/W0.1
32Example 2 Split-Finger Fastball
85-90 mph 1300 rpm (top) 12 revolutions 0.46
sec M/W0.1
33Example 3 Curveball
70-80 mph 1900 rpm (top and side) 17
revolutions 0.55 sec M/W0.25
34Example 4 Slider
75-85 mph 1700 rpm (side) 14 revolutions 0.51
sec M/W0.15
35Effect of the Stitches
- Obstructions cause turbulance
- Turbulance reduces drag
- Dimples on golf ball
- Stitches on baseball
- Asymmetric obstructions
- Knuckleball
- Two-seam vs. four-seam delivery
- Scuffball and juiced ball
36Trivia Timeout
Who said...
- "Baseball is 90 mental. The other half is
physical." - "You can observe a lot by watching."
- "If the people dont want to come out to the
park, nobodys going to stop them." - "No one ever goes to that restaurant any more.
Its too crowded."
37Summary
- Much of baseball can be understood with
- basic principles of physics
- Conservation of momentum, angular momentum,
energy - Dynamics of collisions
- Trajectories under influence of forces
- gravity, drag, Magnus,.
- There is probably much more that we dont
understand - Dont let either of these interfere with your
- enjoyment of the game!