The effect of spin on the flight of a baseball

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 5m of flight, and a ruler to measure the total distance traversed. Speeds in the range v=50–110mph and spin rates ω (topspin or backspin) in the range 1500–4500rpm were utilized, corresponding to Reynolds numbers of Re=(1.1–2.4)×105 and spin factors S≡Rω∕v 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 CL is found not to depend strongly on v at fixed values of S.