What force accelerates a car down hill?

[Umaxo]

To put things straight, i don't want to criticize the video. It certainly makes the idea of curved spacetime more accesible. Certainly for beginners accustumed to "ordinary high-school" physics.

It just occurred to me, that this is "I" topic which i read means undergrad, which i googled means someone pursuing bachelor degree. In this level, it could be perhaps good not to ignore that both diagrams are of completely different nature and that, if we try to draw space-time diagram in Newton theory it should be more similar to GR view.

Just a thought i wanted to throw here, of course i don't know your intentions for this video.

 

[Vitro]

No. I said the rubber sheet model cannot explain certain things without invoking gravity. The rubber sheet model is not general relativity. (On a re-read, I see that wasn't entirely clearly written in my previous post).
If you believe this, place a ball on the sheet, stationary with respect to the mass in the centre. Now explain to me why it starts moving without reference to the actual force of gravity. Note also that if gravity plays no role, this experiment ought to work on the ISS. Do you think it will?

I repeat that it is, of course, possible to describe gravity without using gravity. But the rubber sheet model does not do it.

Something like this: https://xkcd.com/895/

 

[A.T.]

In MTW it was shown (chapter 12) that Newtonian gravitation in geometric language can still be described as curved spacetime (i.e. freely falling particle moves on geodesic).

Yes, also see here:
https://en.wikipedia.org/wiki/Newton–Cartan_theory

So basically Newton and GR picture should be much more similar.

The video compares GR to Newton's formulation of his theory, not to its geometrical re-formulation.

 

[sweet springs]

If, according to general relativity, gravity doesn't exist and falling bodies simply follow curved space, what starts them falling to begin with? If a car parked on a hill slips its brakes what starts it rolling downhill, and what force accelerates it?

In case of a hanged man floor keeps supplying momentum to his feet so that he does not fall or move through geodesic. When the floor disappears he starts moving through geodesic. After a while rope around his neck will supply momentum again to prevent him following geodesic. I hope it will be broken off.