Communications satellites are used to bounce radio waves from the earth's surface to send messages around the curvature of the earth. In order to be available all the time, they must remain above the same point on the earth's surface and must move in a circle above the equator. How long must it take for a communications satellite to make one complete orbit around the earth? (Such an orbit is said to be geosynchronous.) Apply Newton's second law to the satellite and find its altitude above the earth's surface.