Centre of Mass...

What is it?The centre of mass of an object is the point at which the mass of the object is thought to be concentrated.The centre of mass of an object is the only place where that object will balance on a point.

CENTRE OF MASS

How do you find it?In a symmetrical object, you would draw along the axes of symmetry and the point where all the lines cross would be the centre of mass.

If the object is an irregular shape, you would make a small hole in the object and hang it from a pin so it could swing freely. Then you would attach a plumb line (a piece of string with a weight attached and draw down the line, before repeating from a different point.

If freely suspended, the object will come to rest with its centre of mass directly below the point of suspension. 

PendulumsA pendulum is a weight suspended from a pivot so that it can swing freely.

Centre of Mass