The gravitational force exerted on an object, according to
classical mechanics, is the product of the gravitational constant,
the object's mass, and the mass of the object exerting the
gravitational force divided by the square of the magnitude of the
position vector starting from the object exerting the gravitational
force and pointing to the object which we are measuring the force
exerted onto. And all of this is times the negative of that same
position vector.