Dear Tom,
When a baseball is hit by a player, does the ball travel farther in hot weather or in cool weather?
— Allen Dickerson
Dear Allen,
Actually, four factors affect the distance a baseball will travel: wind, humidity, temperature and air pressure. Wind blowing toward (as opposed to with) a baseball slows its forward motion and causes it to fall sooner. Air with a higher humidity (actually, a higher dew point) is slightly less dense than drier air, and so the higher the humidity, the farther a ball will travel. And in answer to your question, the density of air decreases with increasing temperature. Therefore, the higher the temperature, the farther a baseball will travel. Finally, air pressure is also a factor. Lower air pressure (as, for example, at higher elevations) means air is less dense and will result in longer baseball flight distances.
