Circular orbit
= Circular orbit
A circular orbit maintains constant distance from its centre of attraction. Its <velocity> changes direction even when its <speed> stays constant. The inward <centripetal acceleration> has magnitude $v^2/r$, so the radial <force> must satisfy $F_r=-mv^2/r$. For a <Newtonian gravitational field> with <standard gravitational parameter> $\mu$, this gives $v=\sqrt{\mu/r}$.