  Modified Newtonian dynamics proposed that gravitational field needs
modifications when the field strength $g$ is weaker than a critical value
$g_0$. This has been shown to be a good candidate as an alternative to cosmic
dark matter. There is another way to look at this theory as a length scale
dependent theory. One will show that modification of the Newtonian field
strength depends on the mass distribution and the coordinate scale of the
system. It is useful to separate the effective gravitation field $g(r)$ into a
small scale (or short-distance)$g_s$ field and a large scale (or a
long-distance) $g_l$ field that should be helpful for a better understanding of
the underlying physics. The effective potential is also derived.
