An object in motion will stay in motion, unless acted upon by an external forcepic.twitter.com/GVjVVOSQLg
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This is what my twitter @ means The observers in the bed of the truck are moving at a 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 We call such observers 𝑖𝑛𝑒𝑟𝑡𝑖𝑎𝑙 observers Einstein’s postulate states: “any two inertial observers must agree on the same laws of physics”
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Depending on whether you want to call gravity a force, the observers sitting on the truck can be noninertial: the normal force accelerates them upwards through curved spacetime yet they don't move wrt coordinates, while the inertial falling guy has 0 force and moves on a geodesic
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right! i was using the SR definition of inertial observer .. thought this definition is modified in GR a bit
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Galilei, giving the basis of Physics, explicitly described the principle of relativity between observers moving at const velocities. It was expressed in the incredibly complex and baroque Italian of 1600, but it was precisely that.
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He wrote to imagine an observer in a ship, not seeing its uniform motion w.r.t. to the sea. The Einstein elevator of 1600
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I just talked about this too on a tweet about SR https://twitter.com/usmankayaniphd/status/1176210439014952962?s=19 …
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