Orbital Speed

Comparing the centripetal force with Newton's law of gravity gives: $$m\frac{v^2}{r} = G\frac{Mm}{r^2}$$ Solving this equation for $v$ results in: $$\boxed{v = \sqrt{\frac{GM}{r}}}$$ This equation states that the speed of a celestial body decreases with the square-root of the distance to the central body.