Which equation expresses gravitational force between two point masses?

Which equation expresses gravitational force between two point masses?

• A. F = G (m1 m2) / r^2
• B. F = G (m1+m2) / r
• C. F = k q1 q2 / r^2
• D. F = G m1 / r^2

Answer: (A)

Two point masses attract each other with a force that grows with the product of the masses and falls off with the square of the distance between them, along the line between their centers. The expression F = G m1 m2 / r^2 embodies this idea, with G as the gravitational constant. The other forms aren’t right: combining the masses additively isn’t how gravity works; using charges and a Coulomb-like constant describes electric forces, not gravity; and leaving out one mass misses a key factor on which the force depends. So the product of the two masses over the distance squared is the correct description of gravitational attraction.

Two point masses attract each other with a force that grows with the product of the masses and falls off with the square of the distance between them, along the line between their centers. The expression F = G m1 m2 / r^2 embodies this idea, with G as the gravitational constant. The other forms aren’t right: combining the masses additively isn’t how gravity works; using charges and a Coulomb-like constant describes electric forces, not gravity; and leaving out one mass misses a key factor on which the force depends. So the product of the two masses over the distance squared is the correct description of gravitational attraction.