There is a force of attraction between any two particles in the universe. Thus, every particle attracts every other particle with a force,F, given by F = Gm1m2 where m1 and m2 are the masses two particles at distance x apart, and G is the universal gravitational constant, which is now put at 6.672 59 x 10-11 m3 kg-1 s-2. Real bodies having spherical symmetry act as point masses positioned at the center of mass.
See Biomechanics, Center of gravity, Center of mass, Force, Mass, Newton’s laws of motion, Newtonian (or classical) mechanics