When will the motion of a simple pendulum be simple harmonic?
As consider a pendulum of length l and mass bob m is displaced by angle θ as shown is figure. The restoring force =F=−mgsinθ If θ is small then sinθ=θ=radiusarc=lx ∴F=−mglx or Fα(−x) (∵m, g, l are constants) Hence the motion of simple pendulum will be simple harmonic for small angle θ.
