Moment of Inertia – Class 11 | Chapter – 7 | Physics Short Notes Series PDF for NEET & JEE

Moment of Inertia: Moment of inertia is a physical property of a body that quantifies its resistance to rotational motion. It is a measure of how difficult it is to change the rotational motion of an object. Moment of inertia depends on the mass and the distribution of mass around the axis of rotation.

The moment of inertia of a rigid body can be calculated using the formula:

I = ∫ r2 dm


  • I is the moment of inertia
  • r is the perpendicular distance from the axis of rotation to the element of mass dm, and
  • the integral is taken over the entire mass of the body.

Applications of Moment of Inertia

The concept of moment of inertia is important in various areas of physics and engineering. Here are some of its key applications:

  • Rotational Motion: Moment of inertia plays a key role in the study of rotational motion. It is used to calculate the rotational kinetic energy of an object, which is given by K = (1/2)Iω^2, where ω is the angular velocity of the object.
  • Stability of Structures: The moment of inertia is an important factor in determining the stability of structures. By designing structures with a higher moment of inertia, engineers can increase their resistance to bending and buckling under external loads.
  • Design of Rotating Machinery: Moment of inertia is also important in the design of rotating machinery, such as turbines and engines. By designing components with the appropriate moment of inertia, engineers can ensure that these machines operate smoothly and reliably.
  • Dynamics of Systems: The moment of inertia is an essential parameter in the dynamics of systems that involve rotational motion, such as the motion of planets around the sun or the motion of gyroscopes.
  • Conservation of Angular Momentum: The moment of inertia is a key factor in the conservation of angular momentum. In a closed system, the total angular momentum remains constant, and changes in the moment of inertia can result in changes in the angular velocity of the system.

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By Team Learning Mantras