Wimbledon Weatherwatch: high humidity and the Wimbledon tennis championships

When the new Centre Court roof was brought into action at Wimbledon, Andy Murray complained about an increase in humidity. This led to speculation about what physical effects high humidity has on a game of tennis. And contrary to what you might expect, humid air is less dense than dry air, as water molecules are lighter than the oxygen and nitrogen molecules they displace. Air resistance is closely related to density, so the ball suffers less drag and flies fractionally faster in humid air. The lower air density also reduces the Magnus Effect, which causes a spinning ball to swerve in flight and makes a ball with topspin dip downwards. However, in conditions of high humidity the surface of the ball becomes damp and it picks up weight. It bounces less well, and because it weighs more, a given stroke will not propel a wet ball as fast as a dry one. Humidity actually slows things down. It also affects the playing surface; Daniel Gimeno-Traver slipped while playing Murray because the grass was slick with condensation. These are fairly minor effects compared with the impact on the players themselves. Murray said it felt like being "in a bath." Humidity prevents perspiration from evaporating, so players feel hot and sweaty, and dehydration is more of an issue. But the All England Club later claimed that the humidity inside the enclosed court was actually lower than outside during Murray's match. So perhaps it was not the humidity at all.