Define the centre of gravity (C.G) of a body.

Explanation

The centre of gravity of a body is defined as that point where the total gravitational troque on the body is zero.
i.e. `vectau_g=sumtau_i=sumvecr_ixxvecF_i=sumvecr_ixxm_ivecg=0`
where `vecr_i` is the position vector of `i^(th)` particle and `m_1` is the mass of the `i^(th)` particle.