1. The problem statement, all variables and given/known data http://imgur.com/a/X7mWA 2. Relevant equations 1. ΣF = m a 2. Στ = Iθ" 3. The attempt at a solution First , assuming small motion, all movement of the scale can disregard x components (so the spring stretches only in vertical direction without an impact from the x directional movement). I summed torque around the pin, point O, which would be equal to the mass moment of inertia * theta double dot. so... mgL2 - kx1 = I0θ" (mass force positive since displacement is positive in the negative y direction) x1 is the spring movement upwards, however we want to relate that to the x displacement downwards with the mass, which we'll just call x. Now, using like triangles, x1=(L1/L2)x. Then I know x = rθ, differentiate with time twice to get x" = r θ" so then θ" = x"/r, where r = L2. Now we have ... (I0/L2)x" - k(L1/L2)x= mgL2 ===> (I0)x" + k(L1)x = mgL22 This answer just doesn't feel right. I feel like I may not have correctly applied newtons 2nd law or maybe didn't correctly set up the kinematics. Any input would be helpful, thanks.