Welcome to Physics Friday! I would be happy to receive suggestions for future topics based on questions YOU have relating to baseball and science/physics/mechanics: you can drop them in the comments below or reach me at michael@btoolbox.org.

As mentioned by everyone from Dr. Alan Nathan on Twitter to Ben on the latest episode of Effectively Wild, the sweltering temperatures in Los Angeles during Games 1-2 of the 2017 World Series might very well have contributed to enhanced distance on a few home runs that otherwise would have found gloves or grass.

Using the same approach I employed in an earlier post on FanGraphs Community Research, let’s consider how the dimensions of Dodger Stadium could be “scaled” in different meteorological conditions. I had previously done this analysis when comparing the warm, dry March conditions in Cactus League spring training games compared to the cool, humid April conditions most teams will experience at their first few games of the regular season.

Air expands at higher temperatures, decreasing density. A ball traveling through warm air will have to push fewer air molecules out of the way of its path (molecules that cause drag on the ball in flight) than a ball traveling through cold/dense air. As a simple way of accounting for the enhanced fly ball distance, I changed the “effective distance” to the walls in an attempt to keep the number of home runs constant. This approach builds in the spirit of the spectrum spanning No-Doubter to Lucky Homer you can see on the ESPN Home Run Tracker.

If our reference temperature is (for example) 75 degrees, the fences would effectively come in when the temperature is warmer and go out when the temperature is colder. Balls hit to the warning track in 75-degree weather would be much more likely to leave the field if the same contact occurs when the air is 95 degrees. Let’s consider all of the postseason home runs hit in Dodger Stadium so far.

Some of the home runs hit were true No-Doubters. Balls hit 450 feet to straight center will be out of the park in nearly every situation. If we look at the World Series Games 1-2 home runs by launch angle and exit velocity (colored by pitch velocity, thanks to the wonderful tools at MLB Baseball Savant), we can see what the stadium overlay (and the eye test!) showed us: some were well-struck, some were quite weakly hit.

That ball hit at 107 mph and 32 degrees was the lead-off home run hit by Chris Taylor, and the video can confirm that it was absolutely crushed. But many of the other home runs were potentially marginal even in the sweltering heat. How would they have done in a cooler evening?

Using the same calculations I employed in my FanGraphs piece on temperature and humidity and the Trajectory Calculator made by Alan Nathan, I determined that an identically struck fly ball in Dodger Stadium will have an increased distance of approximately 1.7% when the air temperature increases from 75 degrees (climatological average for KLAX on October early evening) to 95 degrees (indicative of the actual air temperatures in Games 1 and 2). Since the fence of Dodger Field doesn’t actually move, in order to understand where fly balls would have ended up if the temperature was 20 degrees cooler, I have scaled the fence outward by about 2% in the graphic above. Lots of those first-row home runs now look like they might be on the other side of the fence. This isn’t conclusive by any means, and each home run could be explored in terms of the instantaneous temperature at the moment of bat-ball contact; however, the popular narrative that the ball is “definitely” juiced seems less likely than the simple fact that hitters were getting an assist from Mother Nature.

Another angle that I wanted to pursue when brainstorming this article was whether the change in home field advantage made any difference this season. Would these balls have been played any differently at Minute Maid Park? If the dome was closed and the temperature was controlled, there wouldn’t be much need to scale the walls according to the weather.

It’s quite possible that some of the wall-scrapers to center and center-right would have instead been doubles off the Houston wall. However, nearly everything sent to left field would have likely been a home run anyway. It’s possible that many other fly balls sent to left would have also left the field of play, but that kind of analysis might be more interesting once the entire series is done.

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Michael is a PhD Candidate in Atmospheric Science in the Department of Earth, Atmospheric, and Planetary Science (EAPS, Course 12) at MIT. Along with three other sports-inclined MIT friends, he co-founded the baseball toolBOX (www.btoolbox.org) research venture, which aims to use analytical methods from fields such as atmospheric science and electrical engineering to discover actionable insights in baseball physics and mechanics. You can reach him with comments, questions, and juiced-ball conspiracy theories at michael@btoolbox.org

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