This equation computes the drag force on a football.
The equation for drag force is `F_d = 1/2 * rho * A *C_d * v^2`
We use the vCalc equation, Force of Drag, where we have set the air density, `rho`, to be a default air density of 1.2754 `(kg)/m^3`.
We use the drag coefficient for a cone (see again the Force of Drag vCalc equation) of 0.50.
The cross sectional area of a football, `A`, is defined by the vCalc constant, Maximum Football axis_1 or axis _2 - NCAA, (which we call `R`) and we use `R` as the radius of the cross sectional area. So, the area is defined as `A = pi * R^2`.
From the paper by Horn and Fearn, we estimate the default velocity of a well-thrown football to be `20 m/s`