What s the deal with the humidor
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Alan Nathan University of Illinois a-nathan@illinois.edu. What’s the Deal with the Humidor?. El Tiante. Humidors in the News. First this. Then this. Some of the News is Controversial. Tim Lincecum. Even Scientists Get in the Act. Why the Humidor in Denver?.

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What s the deal with the humidor

Alan Nathan

University of Illinois


What’s the Deal with the Humidor?

El Tiante

Humidors in the news
Humidors in the News

First this

Then this

Why the humidor in denver
Why the Humidor in Denver?

Thin air means better “carry”

  • Mile high  air density 80% of sea level

  • More home runs!

  • Let’s take a look

The carry of a fly ball


The “carry” of a fly ball

  • “carry” ≡ (actual distance)/(vacuum distance)

    • for same initial conditions

What s the deal with the humidor

HITf/x + Hittracker Analysis:4354 HR from 2009


Thin air more carry more home runs
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?

Home runs and humidors
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
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?

Effects of humidity on ball properties
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

These effects can be measured

So here s the plan
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

Physics alert
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

Summary of findings with rh increased from 30 to 50
Summary of Findingswith RH increased from 30% to 50%

  • Weight increases by 1.6%

  • COR decreases by 3.7%

  • Diameter change negligible

  • 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
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

Final result
Final Result

  • Actual reduction = 25%

  • Calculated reduction = 27.5±4.3 %

  • The agreement is amazingly good


And what about phoenix
And what about Phoenix?

  • If RH goes from 20% to 50%

    • HR reduced by 37.0±6.5 %

    • A very big effect!

More stuff from nick


More Stuff from Nick….


Final summary
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