When a satellite of mass m revolves in a circular orbit of radius r, around the earth of mass m, the gravitational attraction of earth provides the required centripetal force .
According to law of conservation of momentum if no external torque acts on the satellite, then its angular momentum L is conserved. Since, the air friction will provide a retarding torque to satellite, therefore, there will be decrease in angular momentum of the satellite in air.^As a result of it, the velocity of satellite increase according to relation