Physics Lesson 7.2.2 - Moment of Inertia

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Welcome to our Physics lesson on Moment of Inertia, this is the second lesson of our suite of physics lessons covering the topic of Dynamics of Rotational Motion, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

Moment of Inertia

Moment of inertia, I in the rotational motion is the analogue of mass. It is a quantity expressing a body's tendency to resist angular acceleration, i.e. to change in the actual state of rotation. Moment of inertia is the sum of the products of the mass of each particle in the body with the square of its distance from the axis of rotation. Moment of inertia therefore is quantitative measure of the rotational inertia of a body.

Mathematically, we have:

I = m × r2

Obviously, the unit of moment of inertia is [kg × m2] as mass is measured in kg and radius in metre (radius here is raised at power two).

Look at the figure:

Physics Tutorials: This image provides visual information for the physics tutorial Dynamics of Rotational Motion

Example 1

A 2 kg object rotates around a fixed axis at 3 m away from it as shown in the figure above. What is the moment of inertia of this object?

Solution 1

Applying the equation of moment of inertia, we obtain:

I = m × r2
= 2 kg × (3 m)2
= 18 kg × m2

You have reached the end of Physics lesson 7.2.2 Moment of Inertia. There are 8 lessons in this physics tutorial covering Dynamics of Rotational Motion, you can access all the lessons from this tutorial below.

More Dynamics of Rotational Motion Lessons and Learning Resources

Rotation Learning Material
Tutorial IDPhysics Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
7.2Dynamics of Rotational Motion
Lesson IDPhysics Lesson TitleLessonVideo
Lesson
7.2.1Moment of Force as Analogue of Force in Translational World
7.2.2Moment of Inertia
7.2.3Moment of Inertia in Different Systems of Rotational Motion
7.2.4Newton's Second Law for Rotational Motion
7.2.5Angular Momentum
7.2.6Work in Rotational Motion
7.2.7Kinetic Energy in Rotational Motion
7.2.8Power in Rotational Motion

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