-- The relationship between the distance from the planet's center and the force of gravity on the ship has been graphed. That's the reason for the labels on the axes.
-- The distance from the planet's center is labeled in multiples of the planet's radius.
The force of gravity on the ship is labeled in multiples of 1 million newtons.
-- The force of gravity on the rocket at the planet's surface (1 radius from the center) is 4 million newtons. (about 899,203 pounds)
-- The force of gravity on the rocket at a distance of two units (twice the planet's radius from its center) is 1 million newtons.
-- In general, as the distance between the rocket and the planet increases, the force of gravity pulling on the rocket decreases.
From our studies of the nature of gravity, we know that the force is inversely proportional to the square of the distance between the center of the rocket and the center of the planet. We might not notice it from the graph, because there's only one labeled point that clearly shows it. (2radius, 1/4 of the surface force).
If we have been really attentive to our studies and have done all of our gravity homework, we know that the equation of the purple line on the graph is
Force = (4 million newtons) / (Distance)² for Distance >= 1 radius.
