This is just an ordinary differential equation for the coordinates.
Since this is one and the same force the ordinary differential equation follows.
It is a coupled system of linear ordinary differential equations.
This is usually the method we use for complicated ordinary differential equations.
Suppose we have an ordinary differential equation in the complex domain.
This is an ordinary differential equation of second order.
Many problems involving ordinary or partial differential equations can be cast in this form.
In such a case, the problem devolves to N ordinary differential equations.
As always, these are second order nonlinear ordinary differential equations.
They are typically modeled as a set of coupled ordinary differential equations.