Does the relativity of motion depend on gravitational forces?

All motion is said to be relative, thus a train is moving relative to the Earth, the Earth is moving relative to the Sun, etc. Motion is defined to be a change in distance divided by a change in time. General Relativity says clocks run slow in a gravitational field. This seems to imply that the effects of gravity must be considered a factor in motion. Should the idea of relative motion be changed as follows "All motion is relative ONLY IF the sources of motion are in equivalent gravitational fields?|||General relativity says that gravity is indistinguishable from acceleration, and hence a frame with gravity is not inertial.





This has to be taken into account when transforming between frames.|||Yes. All gravity affects everything relative. The moon even affects our oceans tide, so it is safe to say that everything, rotation of the Earth, the Earth's gravity, the moon's gravity at different stages or cycles, the amount of power applied, etc., all affects or is relative to another.|||hmm, not really.. einstein defined gravity as a geometry such that a high gravitational field creates a massive curvature in space-time, such when light passes, it follows the geodesic line, shortest possible route, and thus altering the light cone.