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.

Explanation

(i) During its rotation about its axis, earth comes to the same position again and again in equal intervals of time. Hence, it is a periodic motion. However, this motion is not simple harmonic. This is because earth does not have a to and fro motion about its axibr.
(ii)An oscillating mercury column in a U mercury moves to and fro on the same path, about the fixed position, with a certain period of time.