UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 1

Hitting Home Runs:How a Physicist Thinks About Baseball

Alan M. NathanUniversity of Illinois at Urbana-Champaign

a-nathan@uiuc.edu

http://www.npl.uiuc.edu/~a-nathan/pob

My day job… experimental nuclear/particle physics

high-speed collisions between subatomic particles

Nights and weekends... physics of baseball

high-speed collision between baseball and bat

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 2

Hitting the Baseball

“...the most difficult thing in sports”

--Ted Williams

BA: .344SA: .634OBP: .483HR: 521

#521, September 28, 1960 Aerodynamics of ball The ball-bat collision

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 3

Here’s Why…..(Courtesy of Robert K. Adair)

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 4

Trivia 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 Williamscorrect

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 5

The Ball-Bat Collision

forces large (>8000 lbs!) time is short (<1/1000 sec!) ball compresses, stops, expands bat compresses ball….ball bends bat hands don’t matter! to hit a home run, you need...

large hit ball speed

the right take-off angle

backspin

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 6

Trivia TimeoutWho 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

correct

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 7

What Does Hit Ball Speed Depend On?

Pitched ball speed & bat swing speed

bat speed matters much morevhit = 0.2 vball + 1.2 vbat

Weight and weight distribution of bat what is ideal bat weight?

Bounciness of ball is it “juiced”?

Impact location along bat “sweet spot”

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 8

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 9

The Sweet Spot

60

70

80

90

100

2 3 4 5 6 7 8 9distance from knob (inches)

Hit Ball Speed (MPH)

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 10

Who is this guy and what was his number?

Trivia Timeout

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 11

Wood versus Aluminum

Thin shell …. Lighter CG closer to hands…easier to swing fatter barrel, thinner handle “trampoline” effect

golf driverstennis racketscorked bats?

Net result:

higher batted ball speed

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 12

Trivia 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

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 13

Aerodynamics of Ball in Flight

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 14

The Flight of the BallReal Baseball vs. Physics 101 Baseball

Role of Drag

Role of Spin

Atmospheric conditionsTemperatureHumidityAltitudeAir pressureWind

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 15

Spin on the Hit Ball

Friction induces spin for oblique collisions

Spin => 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

batball

topspin ==>F down backspin==>F up

sidespin ==> hook

bat

ball

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 16

The Home Run Swing

• Ball arrives on 10o downward trajectory

• Big Mac swings up at 10o-15o

• Undercuts ball by 1”-1.25”

• Ball takes off at 35o with lots of backspin

The optimum home run swing!

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 17

Who is this guy?

A) Joe Torre

B) Don Zimmer

C) Lou Skizas

D) Roger Maris

Trivia Timeout

correct

UIUC Alumni Associations, Orlando and Tampa Chapters, March 2002 Page 18

Summary

Lots of physics in baseball

Knowledge of physics helps understanding

of game

And it’s fun too….