center of gravity

engineering

radius of gyration 

if the entire area of lamina is concertated at a point that there is no change in the moi about a given axis then distacne of the point from given axis is called rasius of gyration

parallel axis theorm

the moi of the plane at any axis of area is equal to the sum of the moi about parallel centroidal axis and product of squre of distance between them

perpendicular axis theorm

the moment of inertia about an axis perpendicular to its plane is equal to the sum of the moments of inertia about two perpendicular axes lying in the plane and intersecting at the same point.

center of gravity

It is the point where the whole weight of a body appears to act

centroid

the point where the entire area of the shape seems to be concentrated.