Also needed in equations (1) and (2) are the drag and lift coefficients, CD and CL,
respectively. These aerodynamic coefficients are, in general, functions of both Re and Sp. For
CD, we made use of wind-tunnel experiments [3] on Teamgeist soccer balls. The goal of this
work is to obtain CL for various Re and Sp.
Figure 1 shows the experimental data [3] we used for CD. We note that the data shown in
that figure are for balls with no spin. So that we could extract CD values for speeds that do not
coincide with data points, we created a fitting function ([11], see also [20]3) given by