  Modified Newtonian dynamics by Milgrom is a paradigm for explaining the
rotation curves of spiral galaxies and various other large scale structures.
This paradigm includes several different theories. Here we present Milgrom's
modified inertia (MI) theory in terms of a simple and tractable
non-conservative Newtonian dynamics, which is useful in obtaining observable
predictions of MI. It is found that: 1) Modified inertia theory is equivalent
to a Newtonian theory, with a non-conservative gravitational field, and dark
matter density; 2) The tidal force in the equivalent Newtonian dynamics is
non-conservative, and its effect on a binary system in free fall in the
gravitational field of a spheroid is addressed. We also discuss attempts to
restore conservation in MI.
