Centre of gravity :
All people and objects have a centre of gravity, which can shift depending on the position or movement of the person or object. A centre of gravity is an imaginary point (within or outside the body or object) around which the body or object is balanced.
You can often easily find the centre of gravity on an inanimate object. For example, take a ruler and place it across one finger until it stays horizontal and does not fall to the ground. The point at which it is balancing on your finger is its centre of gravity.
It is not always so easy, however, to find the exact centre of gravity on a human, particulary in sport. In some sports, the centre of gravity shifts very rapidly. For example, during high jump, diving or gymnastics. Remember also that the centre of gravity need not lie within the physical limits of an object or person. Individual body parts, such as limbs, also have their own centres of gravity.