The easiest situation, and probably also the most frequent, consists of imposing a translation velocity. In this case, the velocity components are specified with a possible time-dependence. For 2.5D axisymmetric cases, an angular velocity around the vertical axis can also be specified.

In some situations, it is necessary to describe a more complex motion which combines rotations and translation. Here the description is done in a way similar to that used for describing the motion of moving parts (see Description of Motion). Usually, the combination of the rotation around an axis and a translation of this axis will be enough. The angular rotation is defined around a rotation axis whose initial position is specified with a point and a direction; in turn, a translation is applied to this rotation axis.