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Maybe this channel could be useful for you, they explain the models they use for their other channel, Yarnhub, and describe the capabilities of each machine in quite some detail:    

Of course they aren't the same thing, those would somewhat correspond to independent Newton's laws after all. I was referring to the effects of their combination. What I noticed is that when cavalry change direction they go a bit into each other, and I wondered how their movement would change without doing so. But you say both "it wouldn't much" and "cost more to simulate", along with representing a "balancing change", the latter I think should be considered since far too many sword infantry seemed to be having a go at that poor elephant (avoidance and ranged attacks, mainly javelins if I remember correctly, is how the Romans dealt with them), although of course that's another discussion, but good if "with this PR it's only just one tweak".

You can see how "solid effect" of "stiffness" impact the boats in the video. You get super cool effects when there are a few ones, but a lot of them result in them taking a lot of time to settle. It's fine for boats as you rarely think of crowds of boats, and I just made a scene for this in the video to show that it works, and still look good for them. But if you have a crowd of infantry constantly wiggling and taking forever to settle, this would look very bad. Hence the spring.   Inertia and pushing aren't the same thing. But for navigating on open terrain, this wouldn't change much. However if you try to funnel "solid" physical bodies into a choke-point, they obviously take a while more to achieve the same movement. So if ever we wanted to make cavalry "solid bodies", with this PR it's only just one tweak in their template. But because big crowds of them cost more to simulate and that moving them around take longer if they are in high number, it should be accompanied by an increase of cost/population for example. The pros are that they will have much more realistic charge effects, like you see with elephants, but cavalry have less contact area and are moving much faster, the physic outcome would be different too (like a cavalry can trow fewer infantry units away but at higher velocity). So this is just a balancing change, out of scope. Even without proper "charge", -so just using the old pushing  pretty much as it was, the inertia improves physics for cavalry fighting at no additional cost. The cavalry can push away other spread units thanks to it's superior weight, and also push its target by a little - even if ideally it would be more, and the cavalry would be smart enough to take more advantage of it instead of stopping once in front of it's target. Screencast from 2026-09-22 18-44-41.webm  

0 A.D. 2026-09-22 22-30-22 - Trim.mp4    

Thanks for being upfront, that's useful context. I think the difference between us is one line: you make the civs differ in the data (units, techs) and the AI exploits it; I'm trying to make Petra play the vanilla civs differently, on the data everyone has. Both are valid, and if things like "charge" land in the base game they'll help my side too.  The whole idea rests on a table like this: