Trajectory analysis is an alternative to using wind tunnels to measure a soccer ball’s aerodynamic
properties. It has advantages over wind tunnel testing such as being more representative of game
play. However, previous work has not presented a method that produces complete, speed-dependent drag
and lift coefficients. Four high-speed cameras in stereo-calibrated pairs were used to measure the
spatial co-ordinates for 29 separate soccer trajectories. Those trajectories span a range of launch
speeds from 9.3 to 29.9 m s −1 . That range encompasses low-speed laminar flow of air over a soccer
ball, through the drag crises where air flow is both laminar and turbulent, and up to high-speed
turbulent air flow. Results from trajectory analysis were combined to give speed-dependent drag and
lift coefficient curves for the entire range of speeds found in the 29 trajectories. The average
root mean square error between the measured and modelled trajectory was 0.028 m horizontally a…