Question

Moment of inertia of circle about centroidal axis

Answer 1

The second moment of area, also known as area moment of inertia, is a geometrical property of an area which reflects how its points are distributed with regard to an arbitrary axis. ... If the piece is thin, however, the mass moment of inertia equals the area density times the area moment of inertia.

List of second moments of area - 

Answer 2

Rotational inertia is important in almost all physics problems that involve mass in rotational motion. It is used to calculate angular momentum and allows us to explain (via conservation of angular momentum) how rotational motion changes when the distribution of mass changes.