2026/06/22 by Domenico Giulini · 1 voice
Physics and Astronomy · #Argument (complex analysis) #Experimental and Theoretical Physics Studies #Gravitation #Inertial frame of reference #Motion (physics) #Newton's law of universal gravitation #Newton's laws of motion #Newtonian dynamics #Newtonian fluid #Pulsars and Gravitational Waves Research #Relativity and Gravitational Theory #gr-qc #physics.class-ph
paper · pdf · doi:10.1119/5.0280019
openalex publication_date 2026/06/22 · openalex created_date 2026/06/23 · arxiv published 2026/07/01 · arxiv updated 2026/07/01 · openalex updated_date 2026/08/05
At first glance, combining Newton's laws of motion with his law of gravitation seems straightforward. Students learn to distinguish inertial from gravitational mass and that their empirical equality is a remarkable fact about nature that will later serve as the conceptual gateway to general relativity. However, a closer look reveals a further and often neglected distinction within Newtonian gravity: that between active and passive gravitational mass. A common textbook argument maintains that these must be equal, for otherwise Newton's third law would be violated. We review and critically re-examine this familiar reasoning and show that the supposed theoretical proof is not compelling. Our analysis highlights subtle structural assumptions within Newtonian mechanics and offers physics teachers and researchers a fresh opportunity to explore foundational questions with potentially interesting applications in observational astronomy.