Which of the following examples represent (nearly) simple harmonic motion and which represent periodic but not simple harmonic motion?
(a) the rotation of earth about its axis.
(b) motion of an oscillating mercury column in a U-tube.
(c) motion of a ball bearing inside a smooth curved bowl, when released from a point slightly above the lower most point.
(d) general vibrations of a polyatomic molecule about its equilibrium position.
(a) The rotation of the earth about its axis is a periodic motion(it has a period of 24 hours). But as it is not to and fro motion, it does not represent S.H.M.
(b) The mercury column which oscillates back and forth in a U-tube represents S.H.M.
(c) The ball bearing represents S.H.M as it oscillates to and fro in the bowl.
(d) The general vibrations of polyatomic molecule about its equilibrium position are periodic. But they do not represent S.H.M as it is a superposition of SHMs by individual atoms.