newtonian mechanics - How does the satellite orbiting the Earth, first slows down to some extent, and speed up again to maintain the orbital motion?

We consider that the satellite has time period equal to earth's rotational period, because of equal magnitude of orbital velocity, if that is so, it's at rest relative to earth's rotational motion which carries along the atmosphere at the same velocity so there must have been no air resistance being acted upon the geostationary satellite.