  We investigate whether storing baseballs in a controlled humidity environment
significantly affects their aerodynamic properties. To do this, we measure the
change in diameter and mass of baseballs as a function of relative humidity
(RH) in which the balls are stored. We then model trajectories for pitched and
batted baseballs to assess the difference between those stored at 30% RH versus
50% RH. The results show that a drier baseball may be expected to curve
slightly more than a humidified one for a given pitch velocity. We also find
that the aerodynamics alone would add ~2 feet to the distance a moister ball is
hit. However, this is compensated by a ~6 foot reduction in batted distance due
to the well known change in coefficient of restitution of the ball. We discuss
consequences of these results for baseball played at Coors Field in Denver,
where baseballs have been stored in a humidor at 50% RH since 2002.
