  Up to now, the rotational velocities of galaxies are not clearly understood
and the experimental Tully Fisher rule, linking the total galactic mass to the
fourth power of the velocity, through an acceleration coefficient of about
10-10 m/s2 has not found a deep theoretical explanation. Tentative proposals
(MOND theory of a modified Newton s law and extraneous dark matter) do not
bring a definite clarification. We propose here a new approach to this problem,
without exotic matter and using the classical Newton force. But we introduce a
new additional universal acceleration, which could represent a universal
expansion law valid at the scale level of a galaxy. We show that this
hypothesis leads to a good description of the observed variations of the
galactic transverse velocity. It can be considered as a consequence of the
Scale Expansion Cosmos theory (SEC) introduced by J. Masreliez, but we
postulate that the space expansion acceleration universally applies at any
scale. We obtain a formal derivation of the Tully Fisher law, linking the
constant galactic transverse velocity to its total mass, via the universal
minimum acceleration. We derive a good estimate of the TF acceleration
coefficient and show that expansion should be proportional to the square root
of the local volumic mass density. Our conjecture is in fact a new dynamics
principle which could be applied to many other physical problems at different
scales. Applying it to the range of the solar planet system confirms the well
known Kepler laws, at least as a valid approximation for the order of magnitude
of the solar system.
