What's the nicest proof that two isolates masses orbit their center of mass?
110067
Are planets actually moving in elliptical orbits around the Sun or do they move in circular orbits around their center of mass?
42372
Space Expansion vs. Relative Motion
153552
Relativistic mass as seen by different observers
154951
Is the solution to a question regarding four smaller masses on a rotating hollow sphere accurate?
17998
Is it possible to prove or disprove the Einstein Synchronization Convention with astronomy?
99467
How can I prove that the four-momentum of relativity is conserved like in classical mechanics?
67945
What are good examples to demonstrate Einstein's mass-energy relation
153223
What's the exact gravitational force between spherically symmetric masses?
79727
Direct proof of non-flatness
133178
Are orbits equal if and only if stabilizers are conjugate?
90481
3D donuts and the centre of a black hole
144380
When the Center of Mass and Center of gravity does Not Coincide
37448
Two Circles and Tangents from Their Centers Problem
146782
Why is the period of rotation the same for two stars orbiting the same centre?
9463
What is the proof that the universal constants ($G$, $\hbar$, $\ldots$) are really constant in time and space?
101969
Proof of stars and bars formula
44566
Is (rest) mass conserved in special relativity?