The dependence of baseball lift and drag on spin

Abstract

This study measured the drag and lift of baseballs in free flight as a function of back spin for two spin axes. While others have measured baseball lift and drag, the mechanisms for their dependence on spin have not been explained. For increasing spin, drag was observed to initially decrease then increase at higher spin. The inflection point appears to occur when the flow on the bottom ball surface becomes fully turbulent. At low spin the lift of the four-seam spin axis was nearly constant and three times larger than the two-seam spin axis. The lower lift of the two-seam spin axis was shown to be due to a periodic reverse Magnus effect observed at low spin rates. At higher spin the lift of both spin axes increased at similar rates with spin. As observed with drag, the lift transition point appears to be associated with the bottom of the ball becoming fully turbulent.