I’m glad somebody tried to quantify this. Here’s the rocky ride when taking a late Caltrain bullet from north to south (somewhere before Palo Alto): https://imgur.com/gallery/L3LRcld
I don't think I kept it, but I now understand why it was requested by my friend: I took a video of a thick coin (£1 perhaps, 2.8mm thick) balanced in the train from Malmø to Copenhagen.
I can't remember how long it stayed balanced, at least a couple of minutes, but something like a full wine glass would be fine for the whole journey.
Edit: here's a video of a coin balanced for over 20 minutes on a Chinese HSR train: https://www.youtube.com/watch?v=fumYdO9XknE
I have no words honestly. 150 year old cog wheel trains in the Alps offer a better ride than this.
Honestly that was atrocious. I can't believe people put up with it. That's a roller coaster ride, not a commuter train. With that sort of movement, you can't eat, drink or do any work. You are lucky to be able to have a nap.
Because it's an express the train gets up to some high speeds, and this lateral wobbling starts to really get uncomfortable in the long stretches after Hillsdale or so.
Also, this is the balcony, which amplifies the wobbling. The lower level are much more stable, and I switched to sitting in them shortly after taking this video despite the cramped leg room.
And this was probably the car closest to the engine, like the author of this article said to avoid. I usually sat up there because it was the least crowded.