I've driven in mountains (I'm actually in the mountains, with snow on the ground, even, right now) and for 15 years drove manual (I sometimes miss it, but mostly do not, in the same way that I run Debian now and can't be bothered to run a distro like Gentoo anymore), but I literally never thought of pressing the gas pedal as "regulate the intake manifold". I honestly don't even know what an intake manifold is, though I'm sure if I cared enough, Wikipedia would tell me.

Certainly my understanding of it is a bit more nuanced than simply "accelerate", but ultimately.... "press pedal harder, car moves faster" is... fine? Sure, you have to consider road conditions and (if driving manual) your current gear, speed, RPMs, etc., but... I dunno, I still think "press pedal harder, car moves faster" is a useful mental model to have, to some non-zero level of approximation.

Put another way: if I were to think of all the details of what the accelerator of a car actually does under the hood every time I pressed it, and consider the implications of it and allow that to inform how I press the accelerator, I would have precious little time to actually drive the car... like, the things that actually matter, like steering and staying on the road and avoiding other cars and people and whatnot. When I press the accelerator, I think about the effect it's going to have on the car. And I have a good idea of what effect it's going to have based on my experience driving that car (or any car, really). Not based on any knowledge -- knowledge that I lack! -- of what pressing the accelerator actually does.

The thing I tried to hint at is this: When you approach an incline, you'll naturally push down the pedal to keep your speed. Thus, even if you don't articulate it that way, your model of the gas pedal has nothing to do with acceleration. Yes, "intake manifold" is ridiculous, I grant that, but it's much more likely that the model people develop has to do with something like "effort".

The correct way to safely drive a car is intuition – not a "mental model" of anything.

That's why experienced drivers drive so much more safely than novice ones. It's certainly not because in the meantime, they somehow learned how the throttle works internally.

The same basic lesson applies to software. The best design is the one that lends itself most to human intuition. Because when saving a photo from an image editor, users sure as hell aren't thinking "now an inode is created with this and that metadata".

Intuition implies a mental model, just not a conscious one.

Maintaining speed on an incline is still acceleration. Gravity is just also accelerating you in the opposite direction. The problem here isn't with the parent's mental model of how pressing the pedal is supposed to work, it's with your mental model of what acceleration means. It doesn't mean the number on the speedometer goes up.