NCERT Class 11 Physics Physics Part-II: Chapter 6 — 1 INTRODUCTION
This chapter introduces the concept of Oscillations in Physics, building upon previously learned motions like rectilinear and projectile motion. It distinguishes between non-repetitive and periodic motions, highlighting oscillatory motion as a specific type where an object moves to and fro about a mean position. Examples like a swinging cradle, a pendulum, and a boat tossing in water illustrate this concept. The chapter emphasizes the fundamental importance of studying oscillatory motion, linking it to phenomena in musical instruments, sound propagation, atomic vibrations, and AC power supply. It defines key concepts like period, frequency, displacement, and amplitude, which are crucial for understanding periodic and oscillatory motions. The text also differentiates between oscillations and vibrations based on frequency and introduces the idea of simple harmonic motion as the simplest form of oscillatory motion, driven by a force proportional to displacement.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Physics |
| Book | Physics Part-II |
| Chapter | Chapter 6 — 1 INTRODUCTION |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 5 minutes |
| Word count | 946 |
Learning outcomes
- Differentiate between periodic and oscillatory motions.
- Understand the concept of simple harmonic motion.
- Identify examples of oscillatory motion in daily life and physics.
- Recognize the importance of concepts like period and frequency.
Vocabulary
| Word | Meaning |
|---|---|
| Rectilinear motion | Motion along a straight line. |
| Periodic motion | A motion that repeats itself after a certain interval of time. |
| Oscillatory motion | A motion where an object moves to and fro about a mean position. |
| Equilibrium position | The position where no net external force acts on the body. |
| Damping | The gradual decrease in the amplitude of an oscillation due to dissipative forces like friction. |
| Period (T) | The smallest interval of time after which a periodic motion is repeated. |
| Frequency | The number of oscillations or cycles completed per unit time. |
| Amplitude | The maximum displacement of an oscillating object from its mean position. |
| Phase | A measure of the state of oscillation of a particle at a given instant. |
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Practice questions
- What is the difference between periodic motion and oscillatory motion? Answer: Every oscillatory motion is periodic, but every periodic motion is not necessarily oscillatory. Oscillatory motion involves to-and-fro movement about a mean position, while periodic motion simply repeats itself at regular intervals.
- Give two examples of oscillatory motion. Answer: Examples include a swinging pendulum, a child on a swing, and a boat tossing in water.
- Define the period of a periodic motion. Answer: The period is the smallest time interval after which the motion repeats itself.
- What is the SI unit of period? Answer: The SI unit of period is the second (s).
Practice MCQs
Q1. Which of the following is an example of periodic motion?
Explanation: Uniform circular motion repeats itself after a fixed time interval, making it periodic. The other options are generally non-repetitive or not strictly periodic in the context of oscillations.
Q2. Oscillatory motion is characterized by:
Explanation: Oscillatory motion is defined as the repetitive back-and-forth movement of an object around a central equilibrium point.
Q3. What is the term for the maximum displacement from the mean position in an oscillation?
Explanation: Amplitude is defined as the maximum extent of oscillation, measured from the position of equilibrium.
Q4. Which type of motion arises when the force is directly proportional to displacement and directed towards the mean position?
Explanation: Simple harmonic motion (SHM) is a specific type of oscillatory motion where the restoring force is directly proportional to the displacement and acts in the opposite direction.
Q5. The number of oscillations completed per unit time is called:
Explanation: Frequency is the measure of how often a repeating event occurs, in this case, the number of oscillations per second.
Frequently asked questions
What is the main difference between periodic and oscillatory motion?
Periodic motion repeats itself at regular intervals, while oscillatory motion is a specific type of periodic motion involving to-and-fro movement about a mean position.
What is an example of oscillatory motion from daily life?
A child swinging on a swing or a pendulum of a wall clock are common examples of oscillatory motion.
What is simple harmonic motion (SHM)?
SHM is the simplest form of oscillatory motion where the restoring force is directly proportional to the displacement from the mean position and directed towards it.
Why do oscillating bodies eventually come to rest?
Oscillating bodies eventually come to rest due to damping, which is caused by friction and other dissipative forces.
What are the fundamental concepts needed to describe oscillatory motion?
Key concepts include period, frequency, displacement, amplitude, and phase.
How are oscillations related to waves?
Collective oscillations of the constituents of a medium manifest themselves as waves, such as water waves or sound waves.
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NCERT Class 11 Physics — Physics Part-II — Chapter 6 — 1 INTRODUCTION. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.