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I know of an explanation that the Earth is a inertial frame of reference since it is rotating about its own axis, and since this is happening there is a centrifugal "force" or effect which counters the gravitational one. I know this is a fictitious force and I don't really find myself truly understanding anything if I have to use fictitious forces so I'm not satisfied with this explanation.
Also, I know of an explanation that observes this from a non-inertial frame of reference, saying that since gravity is the centripetal force in effect a part of it has to go on rotating a mass on a certain radius form its axis, therefore the "weight" part of the gravity slightly decreases. How is this happening?
If we assume a constant gravitational force on a constant mass on the surface of the Earth, then on the poles it is evident that the weight of the mass would be a consequence of purely the gravitational pull. However, on the equator the gravitational force itself is still the same, how is then the net acceleration decreased thus also the weight?