On the Physical Essence of Angular Momentum

Classical celestial mechanics often treats angular momentum as a fundamental conserved quantity and takes conservation of angular momentum as a precondition to constrain planetary orbital motion. This paper studies the planar orbital motion of planets and carries out deduction only based on inertia and universal gravitation. This paper clearly states that angular momentum as an independent physical entity does not exist. Angular momentum is merely a composite derived quantity. It comes from the coupled motion of celestial inertial momentum and central gravitation. A circular orbit forms when inertial momentum matches gravitational constraint exactly. An elliptical orbit comes from celestial bodies with surplus inertia. Conservation of angular momentum is an apparent feature of motion under central gravitational field rather than the fundamental cause governing celestial orbital motion. This term is acceptable for mathematical calculation. But this composite concept must not be regarded as an independent physical entity so as to avoid misunderstanding of underlying physical mechanisms.