Question

A satellite in low-Earth orbit is not truly travelling through a vacuum Rather , it moves through very thin air. Does the resulting air friction cause the satellite to slow down?

Answer 1

Air resistance causes a decrease in the energy of the satellite-Earth system. This reduces the diameter of the orbit, bringing the satellite closer to the surface of the Earth. A satellite in a smaller orbit, however, must travel faster. Thus, the effect of air resistance is to speed up the satellite!