Caption: An animation of the force of gravity between 2 spheres.

Features:

1. Gravity is always an attractive force, and so the 2 spheres attract each other.

2. The spheres experience gravitational forces equal in magnitude, but opposite in direction, and so gravity is in agreement with Newton's 3rd law of motion.

3. No other forces are acting and the spheres start from being at rest in an inertial frame. Thus they move toward each other and are accelerating in accordance with Newton's 2nd law of motion (AKA F=ma).

4. The larger sphere has more mass, and so has a smaller acceleration also in accordance with Newton's 2nd law of motion: a = F/m.

5. Note that each sphere is spherically symmetric, and so by the shell theorem, its gravity is exactly the same as if all its mass were concentrated at a point at its center for objects outside of its radius.

   By the by, the shell theorem implies the corollary that the gravitational force between 2 spherically symmetric masses is exactly the same as between 2 point masses.

6. By the by, the gravitational force is easily detected for planet scale objects, is detected accurately for kilogram scale objects in the laboratory, and is completely undetectable circa 2021 for atomic scale (∼ 0.1--1 nm) objects---it's just too weak ---and that's the main reason why we do NOT have a good theory of quantum gravity---atomic scale (∼ 0.1--1 nm) gravity is mostly inaccessible to experiment so far.