The whole started with the computer screen – effectively keeping it simple, and with a minimum of 3D ness, so that the quantification of energy looks more and more like juts a bar chart – you may notice the creeping simplification as you look into the first topic of the 14-16 materials. The orange water came later. Both just stand for (so give you a mental representation of) a certain calculated quantity.
Physics acquires a more austere beauty as you move on!
There again, there hints in the literature over the years that “seeing energy as a fluid” in early studies is kind of inevitable – I am just not sure that anyone went for it as we have done in SPT. The inevitability might arise because the alternative is to spend so much time telling people how they cannot think of energy, that they end up mentally paralysed. This is a kind of caricature, but as with all cartoons, I think an element of truth lies there.
I think there is a PhD on forces out there – concentrating on pushes and pulls, but I’ll leave it to the author to promote that.
But there again may textbooks write as if finding the arrows / forces is simply a matter of looking. It ain’t. You need to re-imagine the world.