Summary:

• Centroid C of an area A is a point in the plane of the area where the overall area may be supposed to be concentrated.
• Centre of gravity G of a thin plate of similar surface area A referred to above is a point whereby the whole mass or weight of the plate is supposed to be concentrated. In fact, this is possible to support this plate in a horizontal plane by a tip of the vertically placed single pin at point G.
• The geometric centre of rectangular area or circular area also represents its centroid. Centroid lies on axis of symmetry of the area. While there are two axes of symmetry, the centroid is the point of intersection of these two axes.
• For the triangular area A (or triangular plate of similar area A with mass M and of small uniform thickness), the centroid of A (or centre of gravity of the plate of mass M) is at the point of intersection of the medians of the triangle.
• Generally, any given area may be divided into parts A₁ to A_n for each of area A₁ may be calculated along with the location of its centroid (x_i, y_i) then the position (x, y) of centroid may be calculated as

and