it starts to explain how the solar system stays "together" so to speak, and how the solar system fits into the Milky Way galaxy, and how the galaxies fit together to make a universe of galaxies.
It does this through the idea of the universal force of gravitational attraction (always attractive in N's case) saying that it depends on the masses of the objects concerned, their separation, and a universal gravity constant called G (different from g which is the acceleration of gravity about 10m/s^2)
F=Gm1m2/r^2 is the (inverse square law) force and it applies to all bodies in the universe.
