4.1.1—The weight of an object may be taken as acting at a single point known as

The centre of gravity is the point through which the resultant weight of an object may be taken to act.

For a uniform symmetric object it is often at the geometric centre; for a non-uniform object it depends on the mass distribution. Use the point to calculate moments.

A uniform metre rule has its weight acting at the 50 cm mark, so its own moment about that point is zero.

The centre of gravity need not lie inside an irregular body, and it is not automatically the centre of the drawing.