## Discussion of Note 360(5)

Many thanks, this point is answered in UFT359 by using moving frames of reference. You provided very helpful graphics for these moving frames in UFT359, Section 3, by expressing X and Y in terms of r and theta. For a circular orbit, the frame of reference is X = r cos theta, Y = r sin theta, but for the ellipse and any other orbit it is different. The Lagrange or convective derivative is the derivative in the moving frame, and the latter is defined by observation for each orbit. Therefore v of Eq. (2) is equated with the observed v, and this defines X and Y. In the moving frame so defined, v is perpendicular to r. In the static frame X = r cos theta, and Y = r sin theta, r is not perpendicular to v for the conic sections. However, in the moving frame, r is perpendicular to v because v is proportional to – X i + Y j and r is proportional to X i + Y j. The definitions of X and Y are however different in the moving frame. The use of the convective derivative in this radically new way is a direct consequence of UFT349 ff., already very popular papers.

To: Emyrone@aol.com
Sent: 28/10/2016 20:15:32 GMT Daylight Time
Subj: note 360(5)

As far as I understand the notes, the convective derivative leads to the
general law

bold g = – v^4 / (MG) bold e_r.