Test-particle approximation
= Test-particle approximation
Treating a moving body as a <test particle> neglects its effect on the externally prescribed field. For a small meteorite moving near a planet, $m/M\ll1$ permits neglect of the planet's recoil and replacement of the relative two-body gravitational parameter $G(M+m)$ by $GM$. This is separate from neglecting <drag> or assuming a <Newtonian gravitational field>.