Mechanics of planar particle motion is the analysis of the motion of particles gravitationally attracted to one another which are observed from non-inertial reference frames and the generalization of this problem to planetary motion. This type of analysis is closely related to centrifugal force, two-body problem, orbit and Kepler's laws of planetary motion. The mechanics of planar particle motion fall in the general field of analytical dynamics, and helps determine orbits from the given force laws. This article is focused more on the kinematic issues surrounding planar motion, which are the determination of the forces necessary to result in a certain trajectory given the particle trajectory.