[calex59]

Yes, it would stop in the middle, as you get closer to the center of the earth, gravities pull lessens because all directions are up, there would be no Pendulum effect, the gravity from all other directions would be pushing against the train slowing and then stopping it. A pendulum swings in the same gravitational state at all times, there is no comparison between the two at all.

You cannot fall up,simple as that.

[HiTech RedNeck]

You can “RUSH” up, however. That train would really be moving by virtue of the gravity which had acted upon it as it went down. And in an ideal frictionless environment, the energy it would have by moving in the middle would be just enough to get it back up to the top at the other end.

You don’t know squat about the physics, pal.

[HiTech RedNeck]

Let me give you an even more obvious example: a roller coaster with a “suicide” drop. It comes down a straight away, hits a U-shaped bottom, and goes back up another straight away. If this lacked friction, yes the coaster would “fall up” all the way to its original level from the bottom. Even with friction it would go back up a goodly ways without additional help from motors. This is not like plopping straight down into a pit and smacking square into a bottom.