Question

Which of the following is an example of oscillatory motion?
A) Heartbeat of a person.
B) Motion of earth around the sun
C) Motion of Halley’s comet around the sun.
D) Oscillations of a simple pendulum.

Answer 1

Hint: We need to understand what actually an oscillatory motion is in order to understand and distinguish between the different types of motions given in the option of this problem and find the correct oscillatory motion among the given options.

Complete step by step answer:
We know that an oscillatory motion is a type of periodic motion. Any motion that repeats after a regular interval of time is defined as a periodic motion. The periodic motion can be any motion irrespective of the path followed by the body in motion or irrespective of a starting and finishing point.
An oscillatory motion, on the other hand, is a periodic motion in which a body follows a definite to-and-from motion along a path between two distinct points or passing through a mean position after each completion of the oscillation due to a fixed axis. This makes the distinction between any periodic oscillation and the oscillation motion.
 

The planets revolving around the sun is a periodic motion which repeats yearly. Whereas, the periodic motion of a simple pendulum is a to-and-fro motion about its fixed point is an oscillation motion. So, we can see that the motion of the planets or the comets around the sun or the heartbeat of a person are not an oscillation.
The oscillations of the simple pendulum is the only oscillatory motion among the given options.

So, the correct answer is “Option D”.

Note: The oscillatory motions, the harmonic motions or the periodic motions are often mistreated due to their similarity in the definition of the repetition after a regular interval. But the oscillations involve a fixed axis of motion, which brings in the necessary difference.