Baseball is harder than soccer

Damp balls fly more predictably in baseball - but for a different reason than previously assumed. It is not the slight increase in size and weight that makes the difference in aerodynamics, but the rougher surface.

Boulder (USA) - Dry mountain air changes the flight behavior of baseball balls. But in order to adapt the game situation in the Denver stadium to that in the rest of the USA, the balls have been stored in high humidity for some time before the game. Like expensive cigars, the balls absorb some of the moisture. In fact, as flying objects, this makes them more predictable; launchers, for example, can now control the flight curve better than before.

"In fact, batsmen counted on the so-called 'Denver advantage' (Coors Field advantage) for more successful strokes. Throwers, on the other hand, feared Denver because they blamed the thin air for the failure of bow throws and other typical throwing tricks," says Edmund R Meyer and John L. Bohn. The physicists from the University of Colorado, Boulder, report in a preliminary publication of the information system "ArXiv.org". Denver, Colorado is way higher than any other playing field in the nation: 1,600 feet above sea level, so the air there is far thinner and drier. In order to bring the game situation into line with the rest of the venues, in 2002 the balls were stored in a humidor - a room with a high level of humidity - before games at Coors Field Stadium in Denver. In fact, there was a slight but clear effect on the game statistics afterwards: The previously above-average number of successful hits and home runs decreased as desired, the games became more predictable for away teams.

However, the reason was not, as is generally expected, that a light, dry ball flies further than a heavy, moist ball. The mountain air itself also has no direct influence on the flight line. The aerodynamic properties changed only slightly as a result of the moisture, report Meyer and Bohn. Rather, the throwers now have a better grip, can give the ball a more targeted spin and more precisely influence the flight characteristics. The physicists analyzed the flight characteristics of five baseballs each, which had been stored at 30 percent and 50 percent humidity. The former corresponds to the mountain air in Colorado, the latter to the average atmosphere in the rest of the USA. Analyzes showed that the wetter balls were 0.24 percent larger and 1.6 percent heavier than the drier balls. However, this had only a minor influence on the calculation of the aerodynamic forces that act during the flight. A heavier ball flies a little further, but a larger ball is slowed down a little more by friction. In the end, the wet ball only flies about half a meter further than the dry one, says Bohn.

Instead, the researchers suspect that the air humidity makes the surface of the ball rougher and therefore easier to grip. Throwers had reported that they gave the dry balls less spin and thus had less influence on the direction. Spin effects corresponding to the "banana flank" in soccer were therefore less possible. So it is now the more targeted throws of the throwers that spoil the batsmen's successful strokes. In addition, it is possible that the heavier, slightly less elastic balls now bounce off the racket more slowly and absorb a little less energy when hitting. More research is needed, say the researchers.