Determination of the drag coefficient by analysing the trajectory of a football

Abstract

Two different types of motion were analysed based on video footage using the free software tool named Tracker. One of them involved dropping the football vertically without any spin, the other type was the projectile motion resulted from a goalie punt. The analysis consisted of fitting the time dependence of the coordinates using a sixth order polynomial, then using these functions and other parameters to obtain the drag coefficient as a function of speed and Reynolds number. Similarly to previous works, the drag coefficient showed large differences for the different speeds. The irregularities and asymmetry of the ball also caused the results to be different for the different trials depending on the orientation of the ball, as well as the slight horizontal spin of the ball during its projectile motion. This method can prove to be a useful tool for further studies in a more controlled environment with higher quality new balls.