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Alan M. Nathan,University of Illinois

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Medicine & Science in Sports & Exercise 34(10): 1675-1684; Oct 2002 ... Can a curveball be hit farther than a ... Mont Hubbard, AJP 71, 1152-1162 (2003) ... – PowerPoint PPT presentation

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Title: Alan M. Nathan,University of Illinois


1
Some Topics in the Physics of Baseball
  • Alan M. Nathan,University of Illinois
  • a-nathan _at_uiuc.edu

2
Some Topics in the Physics of Baseball
  • Can a curveball be hit farther than a fastball?
  • Some aerodynamics
  • Physics of the ball-bat collision
  • Why does aluminum outperform wood?
  • How does a baseball bat work?

3
1. Can a curveball be hit farther than a
fastball?Some Aerodynamics
(in direction leading edge is turning)
CD, CM 0.2-0.5
4
Measurements of Lift and DragJoe Hopkins, Lance
Chong, Hank Kaczmarski, AMN
5
Experiment MoCap Data
y ½ ayt2
topspin?aygtg
6
Effect of Spin on Baseball Trajectory
  • Lift
  • scales approx. linearly with ?
  • has major effect on trajectory

7
Oblique CollisionsPutting Spin on the Ball
  • Sliding friction
  • reduces transverse velocity
  • increases ?
  • sliding-to-rolling transition
  • Results
  • Balls hit to left/right break toward foul line
  • Topspin gives tricky bounces in infield
  • Pop fouls behind the plate curve back toward
    field
  • Backspin keeps fly ball in air longer

f
8
Undercutting the ball ? backspin
trajectories
9
? ? larger for curveball
10
In summary.Can a curveball be hit farther than
a fastball?
  • Higher pitch speed ? higher hit ball speed on
    fastball
  • Butmore backspin on curve ball
  • Net result curveball goes farther
  • by a little bit
  • Mont Hubbard, AJP 71, 1152-1162 (2003)
  • See also February 2005 issue of AJP for a debate
    Hubbard vs. Adair

11
Physics Description of Ball-Bat Collision
  • forces large (gt8000 lbs!)
  • time is short (lt1/1000 sec!)
  • ball compresses, stops, expands
  • bat compresses ball
  • ball bends/compresses bat
  • lots of energy dissipated
  • distortion of ball
  • vibrations in bat
  • ball-bat COR related to energy dissipation
  • why is aluminum better?

Courtesy of CE Composites
12
(No Transcript)
13
Wood versus Aluminum
  • Aluminum has thin shell
  • Less mass in barrel
  • easier to swing and control ?
  • but less effective at transferring energy ?
  • Hoop modes
  • trampoline effect
  • larger COR ??

14
The Trampoline Effect A Simple Physical
Picture
  • Two springs mutually compress each other
  • KE ? PE ? KE
  • PE shared between ball spring and bat spring
  • PE in ball mostly dissipated (80!)
  • PE in bat mostly restored
  • Net effect less overall energy dissipated
  • ...and therefore higher ball-bat COR
  • more bounce

15
Trampoline Effect
16
Experimental Modal Analysis
Impact hammer (force transducer) 35 points along
length
Accelerometer fixed location on barrel
FFT Analyzer
Frequency Response Function (accel / force)
Dan Russell, Kettering U.
17
Hoop Modes of Hollow Bats
Lowest hoop mode --that annoying ping
--trampoline effect
18
COR correlated with fhoop
Wood bat
30 on long fly ball
Courtesy of Dan Russell www.kettering.edu/druss
ell/bats
19
SummaryWhy Does Aluminum Outperform Wood?
  • Trampoline effect reduces energy dissipation
  • More pop
  • Longer fly ball

20
Final Summary
  • Physics of baseball is a fun application of basic
    (and not-so-basic) physics
  • Check out my web site if you want to know more
  • www.npl.uiuc.edu/a-nathan/pob
  • a-nathan_at_uiuc.edu
  • Go Red Sox!
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