What is the primary reason that gravitational force changes the direction of a satellite?

The primary reason that gravitational force changes the direction of a satellite is that it acts perpendicular to the motion of the satellite. Gravitational force provides the necessary centripetal force that keeps the satellite in orbit around the Earth or another celestial body.

When an object moves in a circular path, the direction of its velocity is constantly changing, even if its speed remains constant. In the case of a satellite, gravitational force does not work to increase or decrease its speed significantly but rather alters its direction. This perpendicular force ensures that as the satellite moves forward, the gravitational pull keeps it from flying off into space. Instead, it continuously curves its path, resulting in a stable orbit. Therefore, the nature of how gravitational force acts—perpendicular to the motion—is fundamentally linked to the satellite's ability to maintain its orbit.