The integral form of Gausss law for gravity state ∮∂Vg.ds=−4πGm where ∂V is any closed surface, ds is a vector whose magnitude is the area of an infinitesimals small piece or surface ∂V , and whose direction is the outward pointing surface normal, m is the total mass enclosed within the surface ∂V . The left hand side of this equation is called the flux of gravitational field. Flux of gravitational field is always negative (or zero) and never positive.