I understand what the sliders do as you've explained, but I don't know how to use what you've implemented to do what I think I need to do.

I know the spring parameters, so I don't want to manipulate them manually, but I'd like to set them as limits for the line representing the spring. I don't need to change them once they're set. I understand I can just leave the sliders where they are for this.

The way I imagine working the puzzle is to move (rotate) the lid about its hinge with the spring ends fixed to points I've set. So I thought I'd like to move both ends of the spring.

This is something that shouldn't have been that difficult to do in Sketchup so that's why I was trying that Physics plugin. However, I may have to give it a shot in a Windows VM. At this point I'm not so concerned about the forces because I don't even know where I can mount the ends of the spring to allow the lid to close (and open) properly (at all).