Heat Fuels World Series Home Runs

By Tom Risen|October 31, 2017

Heat and low air density are great for hitting baseballs but tough for airplane engines.

Baseball players have long understood that hot days are better for hitting home runs than a cold day, and a new generation of radar and analytics programs like Statcast that monitor Major League Baseball games are making it easier to quantify the effects.

By drawing on those data sources, Alan Nathan, professor emeritus of nuclear physics at the University of Illinois who studied particle accelerators, has spent his retirement perfecting an equation on the average physics of temperature and baseball. Nathan estimates that a 1-degree increase in temperature during a baseball game means that a ball on average will fly one-third of a foot farther, so that if the temperature is 30 degrees warmer at a game, then on average the ball will travel 10 feet farther.

Tuesday’s World Series Game 6 in Los Angeles should be a good test of Nathan’s equation. The game-time temperature is predicted to be about 40 degrees cooler than last week’s opening game temperature in Los Angeles of 103 degrees at first-pitch.

Temperature can be “the difference between a long out and a fence clearer,” Nathan says.

Why does temperature have so much influence on a baseball? Aerospace engineers have no trouble answering this question. The distance a baseball in motion travels depends on the drag from air molecules it has to push through as it moves through the air, so home runs face less resistance from the lower air pressure of high altitudes, or hot temperatures that decrease molecule density in the air. Even humidity decreases air density and drag because water molecules in the air during misty games are lighter than the heavier oxygen and nitrogen that are more numerous in the air during dry weather.

These effects are well-known among aircraft designers. Aircraft wings face less drag gliding through air that is hot or has low air pressure. On the other hand, aircraft engines are challenged by less dense air, says Nicholas Borer, an advanced air vehicle configurator technical lead at NASA’s Langley Research Center in Virginia. Engines need ample oxygen for combustion, so they generate less thrust when conditions such as heat or high altitude lower air density are at play. That’s why runways in high-altitude cities like Denver are built longer: Engines need more time to generate the flight speed necessary for a plane to take off..

Things are similar in baseball circles, where “it’s widely discussed that you might see more runs on a hot day playing the Colorado Rockies than you’re going to get in October in Boston,” Borer says. That said, when it’s cooler at game time, the advantage can flip to the pitcher, because the density increases the effect of putting force or a spin behind a pitch, he says.

“I would also posit that on a hot day at high altitude that pitchers would get less movement on their balls, which means if you have a curveball pitcher, that pitch would be less effective,” he says. “The other thing is that on a dense day your fastball will be slower.”

Of course, no equation exists to explain why so many of the home runs in the record-setting 2017 Series have come in the covered and climate-controlled Minute Man Park in Houston.