Which of the following examples represents (nearby) shm and which represents periodic but not shm.
(i) The rotation of earth about its axis.
(ii) Motion of an oscillating mercury column in a U-tube.
(iii) Motion of a ball bearing inside a smooth curved bowl when released from a point slightly above the lowermost position.
(iv) General vibration of a polyatomic molecules about its equilibrium configuration.

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.