1. The problem statement, all variables and given/known data I have to derive equation of motion for this system. I want to use a moment of force, but i have a problem with moment of force spring. 2. Relevant equations 3. The attempt at a solution What i've done is: M(Fg)=-mgLsinα M(N)=0 M(Fb)=mω^2 Lsinα*Lcosα mL^2*α''=ΣM M(Fs)=?