Centre of gravity

The centre of gravity is the average location of the weight of an object (imaginary point in a body of matter where the total weight of the body may be thought to be concentrated). The location of a body's centre of gravity may coincide with the geometric centre of the body, especially in a symmetrically shaped object composed of homogeneous material. An asymmetrical object composed of a variety of materials with different masses, is likely to have a centre of gravity located at some distance from its geometric centre.

When you try to balance an object the point of support (pivot point), should be on the same vertical line as the centre of gravity. Then the object, no matter what shape, is going to balance. It will be stable if the centre of gravity lies below the pivot point. If the centre of gravity is above the pivot point, even a slight disturbance will pull it off balance. In this experiment the centre of gravity of this assembly has to be below the pivot point. The pivot point is where the toothpick rests on the rim of the glass. The actual centre of gravity must lie in the empty space between the two forks and below the pivot point to achieve stability.