Principal Axes

The product of moment of area is about principal axes.

There will be 2 directions of principal axes which are perpendicular to each other.

Note

For a shape with more than 2 axis of symmetry, all axes through the centroid is a principal axis.

Principal second moments of area

Second moments about the principal axes.

About principal axes second moments of area will be at minimum and maximum.

Centroidal principal axes

Principal axes through the centroid.

Note

Any axis of symmetry is a centroidal principal axis.