Can You Add Inertias?

Moments of inertia for the parts of the body can only be added when they are taken about the same axis. The moments of inertia in the table are generally listed relative to that shape's centroid though. Because each part has its own individual centroid coordinate, we cannot simply add these numbers.

Can you add and subtract moment of inertia?

Moments of inertia of Composite areas

Composite area is made by adding or subtracting a series of “simple” shaped areas like rectangles, triangles, and circles. The Moments of Inertia of these “simpler” shaped areas about their centroidal axes are known.

How do you add mass moment of inertia?

If a body is composed of several bodies, to calculate the moment of inertia about a given axis one can simply calculate the moment of inertia of each part around the given axis and then add them to get the mass moment of inertia of the total body.