  The equations of motion of a charged particle in the field of Yang's
$\mathrm{SU}(2)$ monopole in 5-dimensional Euclidean space are derived by
applying the Kaluza-Klein formalism to the principal bundle
$\mathbb{R}^8\setminus\{0\}\to\mathbb{R}^5\setminus\{0\}$ obtained by radially
extending the Hopf fibration $S^7\to S^4$, and solved by elementary methods.
The main result is that for every particle trajectory
$\mathbf{r}:I\to\mathbb{R}^5\setminus\{0\}$, there is a 4-dimensional cone with
vertex at the origin on which $\mathbf{r}$ is a geodesic. We give an explicit
expression of the cone for any initial conditions.
