This may straddle more advanced physics, but I thought it leaned toward introductory. 1. The problem statement, all variables and given/known data I have been told to find the net energy of a damped pendulum. 2. Relevant equations Obviously the equation of energy for an undamped pendulum is just: E = KE + PE = .5mv^2 + mgh = 0 I know the equation of angular motion for damped pendulum is: ø'' - (g/L)sin(ø) - cø' = 0 3. The attempt at a solution As for the Energy Equation of damped pendulum..I'm not certain. I assume it must be along the lines of E = .5mv^2 + mgh - ∫Fds. where the damping force is some -cv, or cø'. But unlike a damped harmonic oscillator, we're dealing with two dimensions here and that keeps on confusing me. As you can see it's a mess of different variable and I can't quite figure out how to structure a decent equation. To make matters more interesting, after I write the equation I have to take the derivative with respect to time. All points in the right direction appreciated.