Rotational Motion – Stage 1 (Page 1)

Introduction & Basic Concepts (Intermediate + IIT JEE)

Rotational Motion is the natural continuation of Centre of Mass & System of Particles. In this chapter, instead of studying motion of a point, we study motion of a rigid body about an axis.

1. What is Rotational Motion?

A body is said to be in rotational motion if every particle of the body moves in a circle about a fixed axis.

Examples:
• Ceiling fan
• Wheel of a bicycle
• Earth rotating about its axis

2. Translational vs Rotational Motion

Translational Motion:
All particles have same velocity at any instant.

Rotational Motion:
Different particles have different velocities, but same angular velocity.

3. Fixed Axis of Rotation

In rotational motion, the axis may be:

Passing through the body (fan)
Outside the body (door hinge)

Important: Choice of axis is very important in problem solving.

4. Angular Displacement (θ)

Angular displacement is the angle through which a body rotates about a fixed axis.

• SI unit: radian (rad)
• Vector quantity (direction by right-hand thumb rule)

⚠ Common Student Mistakes

❌ Mixing linear and angular quantities
❌ Ignoring axis of rotation
❌ Treating rotation like straight-line motion

Why This Chapter Is Important for IIT-JEE

• Direct continuation of COM
• High conceptual depth
• Frequent multi-concept questions
• Foundation for rolling motion

Next: Stage 1 – Page 2
Angular Velocity & Angular Acceleration

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🔄 Rotational Motion – Phase 3 (Exam Mastery Series)

Advanced exam-oriented thinking series focusing on traps, execution, pressure handling, and topper strategies.

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