A gravitational field is defined by the vector field $${\bbox[5px, border:1px solid black, #F9F7ED]{\bbox[#FAF8ED,5pt]{{ \mathbf{F}=\mathbf{F}(x,y,z)=-\dfrac{{\boldsymbol G}m{\boldsymbol M}}{x^{2}+y^{2}+z^{2}}\mathbf{u} }}}}$$

where $m$ and $M$ are the masses of two objects, one located at the origin $(0,0,0)$ and the other at the point $(x,y,z)$; $G$ is the gravitational constant; and $\mathbf{u}$ is a unit vector in the direction from $(0,0,0)$ to $(x,y,z)$. Here, $\mathbf{F}$ is the force of attraction between the two objects. The force vectors $\mathbf{F}$ are directed from the object at $(x,y,z)$ toward the object at $(0,0,0)$. Figure 7 illustrates a gravitational field.