Why is gravitational acceleration independent of test masses?

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Gravitational acceleration is independent of mass due to the equivalence of inertial and gravitational mass, which is a principle observed in both Newtonian physics and General Relativity (GR). In Newtonian mechanics, all objects fall at the same rate regardless of their mass, while GR explains this phenomenon as objects moving along geodesics in curved spacetime, rather than being acted upon by a force. The discussion highlights that while Newton's laws describe this behavior, they do not provide a fundamental explanation for why it occurs; it is simply an observed fact. In contrast, GR offers a deeper understanding by showing that gravity is not a force but a result of spacetime curvature. Ultimately, both theories yield identical predictions for free-falling objects, affirming that all bodies experience the same gravitational acceleration.
  • #31
F1 / m1 = g. (Inertial masses and forces).
F2 / m2 = G M/r2. (Gravitational masses and forces).
The quantities on the rh sides of both equations are all measurable quantities that don't depend on any assumptions about gravitational and inertial forces and masses. So we can equate the lh sides of both equations and we get F1 / m1 = F2 / m2 . Assuming that inertial mass = gravitational mass, i.e. m1 = m2 the m's cancel leaving the forces equal. So we can equate the rh sides of the first 2 equations:
g = G M/r 2,
which means that gravitational acceleration is independent of the test masses.
 
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