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What Have We Learned from a Decade of Bat Research?

Alan M. NathanUniversity of Illinois, a-nathan@illinois.edu

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NCAA Trends in Home Runs

Q1: Why does aluminum outperform wood?Q2: What changed in 2011?

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“You can observe a lot by watching”---Yogi

Collision is very inefficientBat speed matters a lotBat slows down

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Quantifying “bat performance”

Batted Ball Speed (BBS) under game conditions

BBS depends on–Pitch Speed

• a little–Bat Speed

• a lot– “collision efficiency”

• joint property of ball and bat

What determines collision efficiency?

1. Coefficient of Restitution2. Bat weight

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1. Coefficient of Restitution (COR)

“Bounciness” of ball– ~1/2 for baseball

• Bounces to ¼ of initial height

– bat matters also

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Contribution of Bat to COR:Vibrations and the Sweet Spot!

“sweet spot” outside

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Vibrations, BBCOR, and the “Sweet Spot”

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1234nodes

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Vibrations, BBCOR, and the “Sweet Spot”

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1234nodes

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Why are aluminum bats better?The trampoline effect

Net Result: BBCOR larger Better performance

demo

2. Weight of bat

• Not the actual weight (“swing weight” or “MOI”)– Larger when weight concentrated in barrel– Larger for wood than aluminum

• Higher swing weight means more weight in barrel– Higher collision efficiency

• Higher BBS• Higher swing weight means lower bat speed

• Lower BBS• Two offsetting factors roughly cancel out

– Leaving BBCOR as primary property determining BBS

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An aside: Corking the Bat

• Corking the bat…– increases bat speed– decreases collision efficiency

• Which one “wins”?

Aside: A curious feature• Bat struck at barrel

– Handle starts to move only after noticeable delay

– When reflected wave reaches barrel, collision is over

• Therefore, nothing on handle end matters– knob, handle, grip, …

• Batter could just as well drop bat just before impact!

And here’s the proof:Todd Frazier’s No-Hands HR

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The New NCAA Standard• BBCOR is “surrogate” for BBS

– Since swing weight mostly doesn’t matter• Where to “draw the line”

– 0.500…just barely above wood

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Measuring BBCOR in Lab

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NCAA Trends in Home Runs

science works!~10% reduction in max BBCOR factor of ~2 reduction in HR

Other Issues

• Dealing with composite bats–BBCOR improves with use– “Accelerated Break-In” or ABI

• Effect of ball on bat performance

The bottom line:We know much more than we did 10 yrs ago about how to characterize, measure,

regulate performance of bats

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webusers.npl.illinois.edu/~a-nathan/pob

Thanks for your attention