Portal:Mathematics/Featured article/2007 4

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Einstein further postulated that the presence of the earth bends the space-time inertial paths in some way, making the straight lines of the inertial systems into curves. With this in mind, we can explain ordinary things in a new way. For example, a satellite circling the earth is following an inertial path, with the path being curved by the presence of the earth. Therefore, the gravitational field we feel at the surface of the earth is really a fictitious force like those of other non-inertial frames of reference.