How to find the Centre of Gravity
The centre of gravity of an object is the point at which all the weight of the object appears to act. This means that if we support the object at this point, the moments on each side are equal and so there is no resultant turning effect.
It is easy to find the centre of gravity (CoG) of a symmetrical object - it is the point at which all the lines of symmetry cross:
Irregular shaped objects are more complex and require the use of a plumb line. This is a small mass on the end of a piece of string or thread - it will always hang vertically.
The object is held so that it balances around its point of supension - the pivot point where the object will not move. We can then use a plumb line to mark in a vertical line below this pivot. We know that the CoG will lie on this line.
If we repeat this for various points of supsension, then the CoG will be where all the lines cross: