3.2 The drag force for 10^3 < Re < 10^5

For 10^3 < Re < 10^5, let CD have the constant value 0.5. Then the drag coefficient is


  fdmid = fdeqn[[1,1,2]] /. f[d rho v/m] -> 0.5

Then FD equals k2 v^2, where


  k2 = 0.25 a rho

or, expressing the area of a circle, a, in terms of the diameter, d


  k2 = k2 /. a -> 1/4 Pi d^2

Up to 3. Two Models for the Drag Force