system
Given the following post, respond as if you're commenting on Reddit:
human
Are the physics in Total Recall correct?

For those who haven't seen the movie, it features a tunnel between Australia and Britain, which allows fast travel in a giant vehicle that is dropped down the shaft, to emerge at the other side. I'm fine with that part (and ignoring the impossibility of constructing such a thing), what I'm questioning is the forces experienced by the people in the vehicle.

For the 'downward' leg of the journey, while the vehicle is in freefall, they seem to experience gravity just the same as if they were standing on the surface. When they near the core (going past it rather than directly through), there is a period of weightlessness, then on the 'upward' part of the journey they appear to experience normal gravity again, in the other direction (the seats rotate so they aren't upsidedown). 

So, is this correct?
gpt
If it's a free fall there will be no apparent gravity during the entire journey.

The tunnel was not aligned with the Earth's axis of rotation, which means that the walls of the tunnel will be applying a force on the vehicle. This will result in friction between the vehicle and the walls, so that there will be a force opposing the fall. This will make it not a complete free fall, so that you can experience partial apparent gravity.

The only place where the vehicle then will experience almost no apparent gravity is around the center where the gravity of the planet is zero (all the mass is symmetrically on all sides and cancels out - check the shell theorem).

The apparent gravity will start lower than if you are stationary on the surface and proceed to gradually get lower until you reach the center, where it would start getting higher but now you'd be hanging upside down (hence the flip in the middle).

In this case you'd also need something to "push" the vehicle on it's way up from the center since you'd have lost a lot of energy to friction.

If anyone sees anything wrong with the forces, don't hesitate to correct me.