1. How Does a Baseball Bat Work? Rotary Club, April 17, 2002 Page 1 How Does a Baseball Bat Work? Alan M. Nathan, UIUC a-nathan@uiuc.edu www.npl.uiuc.edu/~a-nathan/pob l My day job…  experimental nuclear/particle physics  high-speed collisions between subatomic particles l Nights and weekends...  physics of baseball  high-speed collision between baseball and bat

2. How Does a Baseball Bat Work? Rotary Club, April 17, 2002 Page 2 Hitting the Baseball “...the most difficult thing in sports” --Ted Williams BA:.344 SA:.634 OBP:.483 HR: 521 #521, September 28, 1960

3. How Does a Baseball Bat Work? Rotary Club, April 17, 2002 Page 3 Here’s Why….. l 90 mph fastball takes about 0.40 sec to reach batter  ~0.20 sec needed to “observe, process, decide”  ~0.15 sec needed for swing  half of “break” occurs in last 0.10 sec l if batter mis-estimates speed by  1.5 mph (0.007 sec)  swing will be early/late by 1’  elevation of ball misjudged by  1”  backspin/topspin makes ball fall less/more l Warren Spahn (greatest lefthander?) said:  “Hitting is timing. Pitching is upsetting timing.” l 30% success rate gets you in Hall of Fame!

4. How Does a Baseball Bat Work? Rotary Club, April 17, 2002 Page 4 The Ball-Bat Collision l forces large (>8000 lbs!) l time is short (<1/1000 sec!) l ball compresses, stops, expands l bat compresses ball….ball bends bat  bat is very flexible! l hands don’t matter! l GOAL: maximize hit ball speed  1 mph  4-5 ft

5. How Does a Baseball Bat Work? Rotary Club, April 17, 2002 Page 5 What Does Hit Ball Speed Depend On? l Pitched ball speed and swing speed of bat  bat matters much more l Weight of bat  also the weight distribution l Bounciness of ball  is it “juiced”? l Impact location along bat  “sweet spot”

6. How Does a Baseball Bat Work? Rotary Club, April 17, 2002 Page 6 Wood versus Aluminum Thin shell …. fatter barrel, thinner handle “trampoline” effect golf drivers tennis rackets corked bats? “ping” vs. “crack” lighter CG closer to hands…easier to swing Regulation of bat performance tennis ball/racket

7. How Does a Baseball Bat Work? Rotary Club, April 17, 2002 Page 7 Summary l Lots of physics in baseball-bat collision l Knowledge of physics helps understanding of game l And it’s fun too….