Area Moment of Inertia
Moment of force about a point is product of the force (F) and perpendicular distance (d) between point and line of action of that is F.d. This moment is also called as 1^{st} moment of force.
If this moment is multiply by perpendicular distance (d) again between point and line of action of the force that is, F.d^{2}. This quantity is called as moment of moment of force or 2^{nd} moment of force or force moment of inertia. If we take the area instead of force it is called as Area Moment of inertia.
Unit of area moment of inertia (A.d^{2}) = m^{4}
For the rectangular body: M.I. about X-X axis; I_{GX}_{X } = bd^{3}/12
For the rectangular body: M.I. about Y-Y axis; I_{Gy}_{y} = db^{3}/12
For the circular body: I_{GX}_{X} = I_{Gy}_{y} = D4/64
For the hollow circular body: I_{GX}_{X} = I_{Gy}_{y } = (D^{4} - d^{4})/64