Central Force Solution 3 A Nexus mindmap Planets move in elliptical orbits with the Sun at one focus 0 1 2 0 The radius vector to a planet sweeps out area at a constant rate 0 0 0 0 1 1 in short time 1 i.e. this is a consequence of the conservation of angular montum 2 1 0 1 The square of the period is proportional to the cube of the semi-major axis 0 0 1 2 3 in one period 1 2 Keplers laws 0 0 0 0 0 1 2 1 0 0 0 1 2 3 Lagrangian 1 "reduced mass" 0 1 2 3 2 0 1 2 0 1 3 example 3 reduced mass 1 Central Force Solution 3