What two conservation laws underpin the physics validating the Newtonian form of Kepler's Third Law in two-body orbits?

Answer

Conservation of Momentum and Energy

The derivation of the relationship stems directly from the application of conservation of momentum (which dictates the center of mass position) and conservation of total energy (kinetic plus potential) throughout the orbit.

What two conservation laws underpin the physics validating the Newtonian form of Kepler's Third Law in two-body orbits?
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