Question

Which of the following are examples of periodic motion?
A. Oscillations of a pendulum
B. The motion of a swing
C. Motion of the Earth around the Sun
D. All of the above

Answer 1

Objects can either be at rest or in motion. In periodic motion, the motion is repeated at an equal interval of times. In simpler terms, the object or body repeats its motion and traces the same path again and again at equal intervals of time. Periodic motions are different from oscillatory motion.

Complete step by step answer:
Let us first understand what periodic motion is and how it is different from oscillatory motion.
Periodic motion is when the motion repeats itself after a fixed interval of time. This motion can be in any form; linear motion, circular motion, parabolic motion or any other motion which repeats itself in equal intervals of time.
Oscillatory motion is the to and fro motion of the body about some fixed position. For a motion to be oscillatory, there must be a fixed position around which the body can perform to and fro motion.
A pendulum performs an oscillatory motion around a fixed position which is at the center of its motion. The pendulum repeats its motion in a fixed interval of time. Therefore, it is an example of periodic motion.
The motion of a swing is much similar to the motion of a pendulum. In case of swing, the swing performs to and fro motion where its motion repeats at a regular interval of times. Therefore, the swing of a pendulum is also an example of periodic motion.
Motion of Earth around the Sun: We experience different weathers on Earth due to the motion of the Earth around the Sun. As we see that weathers repeat year after year thus, the motion of Earth around Sun is also periodic. The time period for this motion is a year.
Clearly, as all them are examples of periodic motion.

So, the correct answer is “Option D”.

Note:
Periodic motion is different from oscillatory motion.
All periodic motion is not necessarily oscillatory.
Period is the smallest time interval after which the motion repeats itself.
Periods have the same SI units such as time.
The motion of swing is periodic only if no external unbalanced force is applied to the system.