The point through which the Whole mass of the body acts, irrespective of the position of the body, is known as centre of gravity (briefly written as c.g.). The plane geometrical figures (like rectangle, triangle, circle etc.) have only areas but no mass. The centre of area of such figures is known as centroid or centre of gravity of the area of the body. It may be noted that every body has one, and only one, centre of gravity.

Centre of gravity of a solid hemisphere from its base is at the distance of 3r/8.