The basic model of Neo-Newtonian Cosmology takes the following form in terms of gravitational potential $\phi$ as primordial, mass density $\rho$, momentum $m$ and $u=\frac{m}{\rho}$ material velocity all depending on a Euclidean space coordinate $x$ and time coordinate $t$ with the dot on top representing differentiation with respect to time:
- $\rho = \Delta\phi$ (inverse square law in differential form)
- $\dot\rho +\nabla\cdot m=0$ (conservation of mass)
- $\dot m +\nabla\cdot (um)+\rho\nabla\phi=0$ (conservation of momentum: Newton's 2nd Law)
A basic property of this model is conservation of energy in the sense that total energy $KE + GE$ with $KE$ total kinetic energy and $GE$ total gravitational energy, does not change over time:
- $\frac{d}{dt}(KE+GE) = 0$ (conservation of total energy)
- $KE = \int \rho\frac{u^2}{2} dx$
- $GE = -\frac{1}{2}\int\vert\nabla\phi\vert^2dx$.
- inertial mass = passive gravitational mass (Galileo's Equivalence Principle EP)
- passive gravitational mass = active gravitational mass (Newton's EP)
- inertial mass = mass $\rho$ in $\rho\frac{u^2}{2}$
- passive gravitational mass = mass $\rho$ in $\rho\nabla\phi$
- active gravitational mass = mass $\rho$ in $\Delta\phi =\rho$.

