System of Particles and Rotational Motion is Chapter 6 of the Class 11 Physics NCERT textbook. This chapter takes things a step forward by introducing motion not just in a straight line, but around an axis. It explains how systems of multiple particles move together, how to calculate centre of mass, and what happens when rigid bodies rotate. Concepts like torque, angular momentum, and the famous Newton’s laws in rotational form are introduced in this chapter.
I decided to write about this chapter because many students find it difficult at first, but once understood, it becomes one of the most scoring topics in Physics. This chapter has strong connections to real life — from wheels rotating to athletes spinning in sports. Also, questions from this topic are regularly asked in JEE, NEET and board exams. Understanding this chapter properly helps in tackling chapters like Gravitation and Oscillations later. Since the NCERT book is the best place to start, having access to the full PDF along with a clear explanation of the content makes it easier to revise and practice.
NCERT Class 11 Physics Chapter 6: System of Particles and Rotational Motion – Overview
This chapter begins by dealing with systems of particles and then moves into the concepts of rotational motion in rigid bodies. It combines the ideas of mass, motion, forces and rotation, giving a solid base for further Physics study.
Key Topics Covered
1. Centre of Mass
- What is centre of mass
- Motion of centre of mass
- Centre of mass of two/more particles
- Centre of mass of rigid bodies
2. Linear Momentum and Angular Momentum
- Conservation of linear momentum
- Torque and angular momentum
- Angular momentum in vector form
- Conservation laws
3. Moment of Inertia
- Definition and significance
- Radius of gyration
- Theorems of perpendicular and parallel axes
- Calculation of moment of inertia for simple objects (rod, disc, ring, sphere)
4. Rotational Dynamics
- Torque as the rotational equivalent of force
- Newton’s second law for rotation
- Rolling motion
- Relationship between angular and linear quantities