Measurements are presented of the Magnus force on a spinning baseball. The experiment utilizes a pitching machine to project the baseball horizontally, a high-speed motion analysis system to determine the initial velocity and angular velocity and to track the trajectory over of flight, and a ruler to measure the total distance traversed. Speeds in the range and spin rates (topspin or backspin) in the range were utilized, corresponding to Reynolds numbers of and spin factors in the range 0.090–0.595. Least-squares fits were used to extract the initial parameters of the trajectory and to determine the lift coefficients. Comparison is made with previous measurements and parametrizations, and implications for the effect of spin on the flight of a baseball are discussed. The lift coefficient is found not to depend strongly on at fixed values of .
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Among aerodynamicists the “Magnus force” is sometimes referred to as “lift,” which is why is called the lift coefficient.
For a two or four-seam fastball, the stitches on the ball intercept the air flow two or four times, respectively, during a single revolution.