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 position. (d) General vibrations of a polyatomic molecule about its equilibrium position.

Answer

`(i)` A polyatomic molecule has a number of natural frequencies and its general motion is the result of the superpositions of simple frequencies. It is found that the resultant motion is harmonic motion.
`(ii)` it is simple harmonic motion.
`(iii)` it is simple harmonic motion.
`(iv)` it is periodic but not simple harmonic motion.