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Viscous damping is not an accurate representation of the resistance experienced by a body that is moving through a low-viscosity fluid such as air or water. Experiments indicate that the damping force is proportional to the square of the velocity. For a simple pendulum consisting of a 25 mm sphere of mass 70 g attached to a 0.5 m long massless link the equation of motion is:

A. $\theta'' + \frac{g}{l}\theta = 0$
B. $\theta'' + \frac{g}{l}\theta - \frac{cl}{m}\theta'^2 = 0$
C. $\theta'' + \frac{g}{l}\theta - \frac{cl}{m}\theta'^2 = F_1 \sin(\omega t)$
D. $\theta'' + \frac{g}{l}\theta = me \omega^2 \sin(\omega t)$