Thin Air More Carry More Home Runs Coors Field in Denver: –Pre-humidor (1995-2001): Rockies home: 3.20 HR/game away: 1.93 HR/game That is a huge effect Since 2002, baseballs stored in humidor –What effect has that had on HR’s? 9
Home Runs and Humidors Coors Field in Denver: –Pre-humidor (1995-2001): Rockies home: 3.20 HR/game away: 1.93 HR/game –Post-humidor (2002-2010): Rockies home: 2.39 HR/game away: 1.86 HR/game 25% Reduction!
Summary and Outline of Talk Thin air results in lots of HR in Denver Humidor has reduced HR by 25% Two questions: –Can science account for the reduction? –Can we predict what might happen in Phoenix? 11
Effects of Humidity on Ball Properties Humid air makes the ball “less bouncy” –“Coefficient of Restitution” (COR) decreases – Ball isn’t hit as hard Humid air make the ball heavier –Ball isn’t hit as hard –But carries better Humid air makes the ball larger –Doesn’t carry as well 12 These effects can be measured
So Here’s The Plan: Measure in lab how RH affects ball properties Use physics of ball-bat collision to predict change in batted ball speed Use aerodynamics to predict change in fly ball distance From all this, we can estimate change in home run production 13
Physics Alert!!! The next few slides will have some details that may bore you Hang in and I’ll tell you when to pay attention again 14
Summary of Findings with RH increased from 30% to 50% Weight increases by 1.6% COR decreases by 3.7% Diameter change negligible 16 For typical long fly ball (100 mph, 30 deg) - Batted ball speed decreases by about 3 mph - Fly ball distance decreases from 415 ft to 402 ft
What about Home Runs? We have full record of every home run hit during 2009 and 2010 (336 total) –Total distance –Batted ball speed and launch angle –Good approximation to full trajectory With changed balls, can ask whether the ball would have cleared the fence –Only 265 make it 17
Final Result Actual reduction = 25% Calculated reduction = 27.5±4.3 % The agreement is amazingly good –SCIENCE WORKS 18
And what about Phoenix? If RH goes from 20% to 50% –HR reduced by 37.0±6.5 % –A very big effect! 19
Final Summary Storing the baseballs in a humidor has resulted in a big reduction in home runs at Coors Field in Denver We understand very well the effects that lead to that reduction We can apply our understanding to predict an even larger reduction if a humidor is employed at Chase Field in Phoenix I like to think that our analysis led the Dbacks to postpone their decision 21 QUESTIONS?
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