Physics of Broken Bat Home Runs

I was listening to the Yankee yesterday, well for no real reason, as Jesus Flores hit a broken bat double off the wall. This was the third moment of a power hit this season due to a broken bat. Earlier in June Giancarlo Stanton hit a broken bat homerun and this past week Chris Davis of the Orioles hit one too.

So this got me thinking, what’s with all the broken bat homers?

Believe it or not, these types of hits are not as rare as you would think. Doing an informal google search shows that a broken bat home run happens about once every season or two.

Being a Physics teacher, I get slightly upset at the television or radio whenever they talk about the strength of the batter, and why he was able to hit a broken bat home run, because the batter strength is only part of this story that goes deep into mechanics.

To be clear, these announcers are absolutely correct about the strength. Stanton is one of the strongest players in baseball and Davis, although lesser known, is developing into a power hitter for the Baltimore Orioles. The force applied to the baseball is a huge contributing factor whether a baseball is going to fly out of the ball park or not.

Ultimately what the batter does to a baseball is he changes the ball’s momentum. Momentum is measured by the mass and velocity of the baseball, mass being a scalar value (a value of only magnitude) and velocity being a vector (having both magnitude and direction). It doesn’t take rocket scientist to realize that when the batter makes contact with a baseball, he is changing the direction of the baseball, thus changing the momentum.

Now there is a more technical term in this, Impulse. Impulse is measured as the change of momentum. However, momentum is really just force multiplied by the change in time.

In a non-abstract example, the longer the bat stays on the ball, the more impulse, more change of momentum etc. So while force plays a role in homeruns, so does bat and ball contact. The more time on the bat, there is more opportunity for an energy transfer from the bat to the ball.

Watch the video from Chris Davis broken bat blast.

With a lot of broken bat hits, that bat shatters immediately. However if you watch this video, Davis is almost done his swing when the main part of the bat comes flying off. Also by looking at how his bat broke, there is a lot of evident energy transfer that occurred.

Finally, look where Davis made contact. He still got the barrel on the bat. If he was jammed inside, we would have a much different result. Jamming inside depletes the amount of torque applied to the ball, increases the chance of the bat being broken, and decreases the amount of time and surface area the bat and ball make. All three lead to a diminished amount of energy transfer.

The last factor that all three of the hits talked about earlier here have in common would be the time of year. It’s June. It’s warm out. The ball flies better in this weather.

At the end of the day, Announcers are correct when they say that it is the strength of the batter that drives the ball out of the park on a broken bat hit, however the time the ball spends on the bat, the amount of torque , and the weather are also factors that contribute to this rare play in baseball.