system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Gravitational Proportionality constant in the equation g = -(G M)/r^2

Really need help for a Physics project and can only find explanations for G when it's an equation using gravitational force between two objects. 
The equation I'm using is for planets or something. (g = -(G M)/r^2)

Any help would be greatly appreciated.
gpt
Any two objects have a gravitational force between them. For most things, they're light enough and far enough apart that we don't notice them.

For objects that have observable gravitational fields, we can clearly observe that the gravitational force "pulling" them together is inversely proportional with the square of the distance.

In other words, when two objects are twice as far away from each other, the gravitational force is 1/4 the strength that it was. If they were triple the distance, the gravitational force between them would be 1/9 the strength, and so on.

Halve the distance between the objects, and the gravitational force doesn't just double; it quadruples.

This is related to the way that space is bent by gravity, and similar equations hold true for light: if you shine a light at me, then move twice the distance away, that light will appear to me to be 1/4 as intense as it was.