1. There is a particular choice of the inertial and gravitational masses . 2. To date, no other accurate method for measuring gravitational mass has been discovered. 3. Gravity is calculated by Newton's law of universal gravitation, which depends on gravitational mass . 4. Why are inertial mass and gravitational mass the same thing? 5. Ever since conservation of momentum requires that active and passive gravitational mass be identical. 6. At high speeds, relativistic mass always exceeds gravitational mass . 7. The semi-major axis is known if the mean motion and the gravitational mass are known. 8. Photons have energy and therefore also have mass in the usual sense of gravitational mass . 9. This is possible because spacetime is radically curved in close vicinity to a large gravitational mass . 10. :Sounds like you are talking about a substance with a different gravitational mass than inertial mass.
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