Center of Gravity
A body and the center of gravity.
The "center of gravity" for a volume, an area or a line  is the point at which the body  if suspended  would be in balance.
For a symmetrical body in a uniform material  the center of gravity would be in the geometric center.
Perimeter
The center of gravity is the center of the circle inscribed in triangle ABC (middle points of the sides of the triangle).
The distance d can be calculated as
d = h (b + c) / 2 (a + b + c) (1)
Triangle
The center of gravity of a triangle is at the intersection of lines BE and AD. The distance a can be calculated as
a = h / 3 (2)
Parallelogram
The center of gravity of a parallelogram is at the intersection of the diagonals.
Trapezoid
The center of gravity of a trapezoid can be estimated by dividing the trapezoid in two triangles. The center of gravity will be in the intersection between the middle line CD and the line between the triangles centers of gravity.
Two Bodies
The center of gravity of two bodies can be calculated as
b = Q a / (P + Q) (3a)
c = P a / (P + Q) (3b)
where
Q, P = weight or mass of the bodies (N, kg, lb, slugs)
Related Topics

Mathematics
Mathematical rules and laws  numbers, areas, volumes, exponents, trigonometric functions and more. 
Mechanics
The relationships between forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more. 
Miscellaneous
Engineering related topics like Beaufort Wind Scale, CEmarking, drawing standards and more. 
Statics
Forces acting on bodies at rest under equilibrium conditions  loads, forces and torque, beams and columns.
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