Lesson: Moment of Inertia Physics • 9th Grade

In this lesson, we will learn how to calculate the angular mass, called the moment of inertia, of rotating objects of various regular shapes.

Lesson Plan

Students will be able to

use the formulae for the moment of inertia of a hoop, disk, sphere, hollow sphere, rectangular prism, cylinder, rod held at its center, rod held at one end, and a point mass orbiting about an axis to calculate moments of inertia,
compare the dimensions of different objects that have equivalent moments of inertia.

Lesson Video

Lesson Worksheet

Q1:

Which of the following formulas correctly relates the moment of inertia of an object, , to the mass of the object, , and the distance of the object from the axis around which it rotates, ?

Q2:

Which of the following correctly shows the SI unit for the moment of inertia?

Q3:

A thin hoop has a radius of 1.25 m and a mass of 750 g. The hoop can rotate around an axis that intersects the hoop at the points A and B, as shown by the blue arrow in the diagram. The hoop can also rotate around an axis that intersects the midpoint of the line from A to B and does not intersect the hoop, as shown by the orange arrow. What is the difference in the moment of inertia of the hoop around these two axes?