Experiment to find the centre of mass of a lamina
You can find the centre of mass of a lamina, a flat object, by hanging the lamina from a point and a plumb bob and line next to it (this is a mass on a string). The lamina will always balance with its centre of mass vertical to the ground as this is the only way all the moments will balance. Draw a pencil line along the line of the plumb bob then hang the lamina from another point and repeat the experiment. The centre of mass should be where the two lines cross. You can check this with a third hanging point.
Beware! The centre of mass of the lamina will not always be within the object itself.
Beware! The centre of mass of the lamina will not always be within the object itself.