In Newton's law of universal gravitation, how does the magnitude of the gravitational force between two point masses change when the distance between them is doubled (masses unchanged)?

• A. It remains the same because distance does not appear in $F=GmM$.
• B. It becomes one-half as large because $F\propto \frac{1}{r}$.
• C. It becomes twice as large because $F\propto r$.
• D. It becomes one-fourth as large because $F\propto \frac{1}{r^2}$.

Answer: (D)