Rotational Motion – Meaning, Terms, and Formulas

What is Rotational Motion?
When a body spins or rotates around a fixed axis , it is said to be in rotational motion.
Example: A spinning top, wheels of a car, Earth rotating on its axis.

Important Terms:

1. Axis of Rotation – The fixed line about which a body rotates.

2. Angular Displacement (θ\thetaθ) – The angle through which a body rotates.

   • Measured in radians .

3. Angular Velocity (ω\omegaω) – Rate of change of angular displacement.

   
   • Unit: rad/s

4. Angular Acceleration (α\alphaα) – Rate of change of angular velocity.

   
   • Unit: rad/s²

5. Moment of Inertia (III) – Resistance of a body to change its rotational motion (like mass in linear motion).

   
   • Unit: kg·m²

6. Torque (τ\tauτ) – Rotational equivalent of force.

   
   • Unit: N·m

Equations of Rotational Motion (Similar to Linear Motion):

Rolling Motion:

A combination of rotational and translational motion.
Example: A rolling ball moves forward (translation) and spins (rotation).

Daily Life Examples:

• Ceiling fan blades.
• Ferris wheel in an amusement park.
• Earth’s rotation causing day and night.

Summary:

Rotational motion occurs when an object spins around a fixed axis. Key quantities are angular displacement, angular velocity, angular acceleration, torque, and moment of inertia.