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
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)
To achieve constant speed you need to balance out the forces going forwards and the forces going backwards, which means there’s no acceleration. This is part of Newton’s first law of motion: every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. So with no visual aid you wouldn’t be able to tell whether you were stationary or acceleration.
OP – did you mean to post this twice?
No, you aren’t. Your body can only detect changes in motion. So you’d have to undergo acceleration of some sort or feel some force on your body.
Acceleration in one direction feels like deceleration in another direction. That’s why you couldn’t tell which direction you were facing even when your speed was changing. Beyond that, you can’t feel yourself moving at a constant speed unless air is hitting you or something like that, you can only feel changes in speed.
Don’t worry about it. We are limited by our senses, and there are some things we simply can never know with utter certainty
We are on a spinning globe, whizzing around the run, flying through the galaxy and we can’t feel that at all. The only way we know we’re moving is by watching the other stars. We can’t feel any of that motion.
Even in a perfect world, you wouldn’t be able to tell direction. Even if the train was accelerating/decelerating/turning, you would be able to tell the direction of acceleration and mangnitude, but not direction of velocity unless you already knew the magnitude and direction of your velocity at any one instant of the journey.
It is impossible to know motion without also defining a frame of reference; it is only possible to detect changes in motion or motion relative to something else. This is the basis of the theory of relativity. Not being able to see outside the train removed any external frame of reference, thus preventing you from knowing your motion.
Similarly, acceleration and deceleration are the exact same thing, and you can only tell which is happening by an external frame of reference. Eg, the only difference is how your motion is changing relative to an outside frame of reference. Deceleration is really not a scientific term for this reason: its just acceleration.
If you are at 45 degrees latitude, you are moving west at about 700 MPH, but notice nothing as the entire surface of the planet is moving with you – you mostly notice this by seeing the Sun and Moon move in the sky. Then the Earth itself is moving around the sun 18 miles/second (30 km/s), but you feel nothing as the entire Earth is moving with you.
On a similar vein, the lack of gravity in space, such as the ISS, is not due to a lack of gravity, but rather because everything is falling exactly the same. The ISS actually has about 90% the gravity as we have at the surface, its just that the entire ISS, and its contents, is falling at exactly the same speed and acceleration* and thus there is no perceptible acceleration, resulting in a lack of gravity. There is actually a plane used by NASA called the Vomit Comet that produces the same effect for short durations – it flies up high then enters a dive that falls accelerates at the exact rate of gravity, resulting in a “lack” of gravity.
Another very interesting case you might have gotten at some point is when you are in a bus, train, or ship, and a vehicle next to you that is blocking the window starts to move. Your brain can get very confused as your eyes are seeing acceleration/motion, but your ears are not picking up acceleration. This can result in a form of motion sickness, which is tightly tied to other forms of motion sickness.
All that said, on a train you do have some outside reference that will be picked up, notably the fact that the track will not be perfectly smooth. This will result in the train bumping up and down, meaning acceleration is occurring, which you can feel. The bumpiness is directly related to how fast you are traveling along the track, and thus you can roughly figure out how fast you are traveling relative to the track by how bumpy the track is. From there, you can figure out, over time, if that rate is increasing or decreasing. You cannot, however, figure out which direction you are moving along the track, without a lot more information about the track.
* As a note, the ISS does actually have a slight difference in acceleration across it due to different distances from Earth, which is a tidal effect, but that amount is so tiny as to not matter for an object the size of the ISS.
If you felt movement all the time, the earth’s rotation would be really dizzying. You only feel acceleration, not movement
You use your memory.
You can detect the acceleration and deceleration in the direction of motion–sideways acceleration will be due to turns.
I’ll up you one…
If you are a windowless box, how do you tell if the box is sitting on a planet or if it is accelerating through space at a constant rate?
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