eli5: At constant speed and no vision, are you supposed to be able to tell if you are travelling forward or backwards? How?

Question

Was on the train and it was pitch black outside. Thought I was sitting facing the direction of travel but turned out I wasn’t.

Even when I felt the acceleration/decelerating, I didn’t know which it was.

In: 16

Answer 1

If you have no visual cues, or wind rushing by, then no, you’ll be unable to tell in which direction you are moving, or how fast, or whether you’re even moving at all. In fact, even if you can see your surroundings, you can’t tell if it’s you that’s moving, or the surrounding landscape is moving past you. Think hard enough about this for long enough, and you might invent the theory of relativity.

As for acceleration, you can feel acceleration as a force. On a train, it will be a force pushing you back into your seat, or pulling you forward. Since you can’t tell which direction you’re already moving, you won’t know if the acceleration is making you faster, or making you slower (sometimes called deceleration)