Question

Which one of the following is not a periodic motion?
A) Rotation of the earth about its axis
B) A freely suspended bar magnet displaced from its ${\text{N - S}}$ direction and released
C) Motion of hands of a clock
D) An arrow released from a bow

Answer 1

Hint: If an object repeats its motion along a particular path, about a certain point, during a fixed of your time, the motion of such an object is understood as periodic motion.

Complete step by step answer:
1. Rotation of the earth about its axis: The rotation of earth about its axis is periodic because it repeats after a regular interval of time. The rotation of earth about a fixed point, hence its motion is not SHM.
2. The motion of a freely suspended magnet, because the magnet oscillates about its position with a definite period of time.
3. Motion of hands of a clock: The hand of the clock is both circular and rotational motion as it’s also a periodic motion. If it has all three-rotational, periodic and circular motion, then the hands of a clock move.
4. An arrow is released from a bow: The string of the bow being stretched, the amount of energy that it took to stretch the string is stored in the string as long as the force keeping it string is intact. When the force is released, the stored P.E. is converted to K.E. which is that the energy of motion.

An arrow released from a bow moves only in the forward direction. Hence, this motion is not periodic.

So the correct answer is option (D).

Additional Information: Difference between Oscillatory Motion and Periodic Motion
Periodic motion is defined because the motion that repeats itself after fixed intervals of your time. Oscillatory motion is defined because the to and fro motion of the body about its fixed position.

Note: Examples of periodic motion, Periodic motion, in physics, motion repeated in equal intervals of your time. For example, a water wave, a rocker, a vibrating implement a swing in motion, the planet on its orbit around the Sun, and a bouncing ball.