  We suggest that there is a novel force which is generated by the mass of
relatively moving particles. The new force which we named Mirinae Force is a
counterpart of the magnetic force operating between electrically charged moving
particles. Instead of using the conventional dark matter, we applied the
mirinae force to a particular model system of the spiral galaxy in which most
of the galaxy's mass is located within the central region where some portion of
the inner mass is in revolving motion at a relativistic speed. The calculation
yielded three important results that illustrate the existence of mirinae force
and validate the proposed model: First, the mirinae force in this model
explains why most of the matters in the galactic disk are in the circular
motion which is similar to cycloid. Second, the mirinae force well explains not
only the flat rotation curve but also the varied slope of the rotation curve
observed in the spiral galaxies. Third, at the flat velocity of 220 Km/s, the
inner mass of the Milky Way calculated by using the proposed model is
6.0\times10^11 M\odot, which is very close to 5.5\times10^11 M\odot (r <50 Kpc,
including Leo I) estimated by using the latest kinematic information. This
means that the mirinae force well takes the place of the dark matter of the
Milky Way.
