According to Newton's law of universal gravitation, the magnitude of the gravitational force between two point masses is $F=G\frac{m{}_{1}m{}_2}{r^2}$. Which variables determine the value of $F$ (assuming $G$ is constant)?

• A. The electric charges of the objects and the distance $r$
• B. Only the distance $r$ between the masses
• C. The masses $m{}_1$ and $m{}_2$ and the acceleration due to gravity $g$
• D. $m{}_1$, $m{}_2$, and $r$

Answer: (D)