Tracking a Spinning Ball, With Math From tennis pros to cricket bowlers, athletes have long known that wind will influence the trajectory of a spinning ball. But until now, research on the topic has tended to focus on topspin or underspin - movement perpendicular to the direction in which the ball is moving. Balls in play rarely behave so well. Two Australian physicists - brothers and lifelong cricket fans - have now devised equations based on Newton's second law of motion that they say explain the influence of wind on balls that are spinning in arbitrary directions. The researchers used computer models to solve the equations, which are written in x, y, z component form, and are intended to help predict the trajectory of a variety of spinning balls in windy conditions. The equations can be applied equally to a number of sports, though the focus in this study was on golf and cricket. For example, they found that a cricket ball thrown by a right-handed bowler with an "off-spin" delivery (in which the ball curves away from a right-handed batsman) will exhibit a lift in the presence of a wind coming from the "off-side" (the right side of a right-handed batsman), but will dip in the presence of a wind coming from the "leg," or left side. The purpose of the paper, which was published in the journal Physica Scripta, is not to help athletes improve their play, but for the love of science and sport, say the researchers, Garry and Ian Robinson. Professional athletes "know empirically many and possibly all of the phenomena exhibited in the modeling work we have done, so we are not trying to tell them their business," Ian Robinson said.