The basic kinematic modes of a fluid

A parcel of fluid undergoes, in general, three distinct types of kinematic behavior, namely:

1. translation,
2. rotation (or spin), and
3. deformation.

In Art. (1.03) and (1.04) the first of these categories of motion was discussed. Translation is essentially the gross motion of the parcel of fluid. The other two phenomenon represent relative motions and distortions superimposed upon the gross movement. All three phenomena are, in general, independent of each other, in the sense that one can occur in the absence of the others. For example, it is possible to conceive of a parcel which has no spin and is not subject to deformation as it moves along a curved path through space. An example is the movement of any solid part of the suspended cage of a Ferris wheel as it traverses its circular path.