[jmiskovic]

Your example with two stacked objects on the digital scale demonstrates force/impulse propagation. The middle object should sense incoming forces and then propagate them onward to other touching objects. If you want to evaluate existing rigid body physics engines, you could examine their implementation of Newton's cradle. In the cradle each ball needs to propagate the received impulse to the last ball it without the ball being moved at all. I've worked with open-source ODE engine and it doesn't do the impulse propagation so you would need a small air gap between balls to transfer the momentum.

That's for theory side. From engineering viewpoint the desire to create from scratch is always strong and most often regretted later. One thing you may not expect, for physics engine to detect and resolve collisions between various shape types (sphere, box, cylinder...), each combination of shapes needs to be implemented separately. This is a lot of code riddled with edge cases just for that feature. Maybe dig through a few papers that describe implementations before starting your own.

[leakbang]

Yeah, at the moment, I'm reading books, papers, and articles on physics engines. I'm still evaluating my approach to the design of the Physics engine.