2. Continuous flow in a moving channel

The fundamental laws of physics are identical in reference systems that move linearly in relation to one another. This was Galileo's experimental observation, taken up by Newton to demonstrate his second law. This second law or fundamental principle of dynamics is therefore only valid in Galilean reference frames (or inertial reference frames). A material point P subjected to one or more forces acquires an acceleration proportional to the resultant of these forces, in a Galilean reference frame (6) .

A point in a rotating wheel obviously doesn't move linearly; we're no longer in a Galilean frame of reference and, as a result, Newton's second law, in particular, can no longer be applied. In this case, the law must be supplemented by new terms.

...