Question

Two uniform spheres, each with mass 𝑀 and radius 𝑅, touch each other. What is the magnitude of their gravitational force of attraction? 

Answer 1

The magnitude of gravitational force of two spheres is given as follows:

$$F = G\dfrac{M\cdot M}{r^2}$$

where $G$ is the gravitational constant, and $r$ is the distance between the centers of the spheres. Since they touch each other, $r = 2R$. Finally, obtain:

$$F = G\dfrac{M^2}{4R^2}$$