Hot, humid air is also less dense than colder air and slightly reduces drag. This helps explain baseballs traveling farther when hit in hotter weather. As the temperature rises, gas molecules in the air move faster and farther apart, lowering resistance to moving objects. And contrary to what many people think, humid air is lighter, not heavier, than dry air because water vapor displaces weightier nitrogen and oxygen molecules.
In places near sea level, like Tokyo, the combination of heat and humidity should result in about a 3 percent reduction in air density (as compared to a 25 percent difference between sea level and the 7,300-foot altitude in Mexico City, the site of the 1968 Summer Olympics), Chapman said.
“Would a 1- to 3-percent change in air density end up affecting performance? It has to,” he said. “It’s just a question of what’s the magnitude and how does that magnitude compare to the 57 other things that can influence an athlete’s performance from mental to physical to everything else?”
The main concerns for sprinters in Tokyo will be remaining properly hydrated and rested; staying out of the sun as much as possible and expending as little energy as necessary to advance through the preliminary rounds.
They might also want to pray for rain.
At the 1968 Olympics, Bob Beamon’s startling long jump, which broke the existing record by nearly two feet, came just before a storm. So did Wyomia Tyus’s world record in the women’s 100 meters. Clearly, altitude influenced those performances. But Powell’s jump that broke Beamon’s record in 1991 also came before a storm, in Tokyo, which is only 130 feet above sea level.
Usain Bolt of Jamaica first broke the world record in the 100 meters following a rainstorm at a meet in New York before the 2008 Beijing Olympics. A light rain followed the setting of his current world record, 9.58 seconds, at the 2009 world championships in Berlin, observers said.
“My focus was always on executing the race and I didn’t care too much about the weather,” Bolt said.
