Recently I visited Shanghai and took a ride in their MagLev train which tops at 431 kph. When it stopped accelerating and kept its constant speed, I was very surprised when I started walking up and down the aisle and felt strange, like I was walking uphill when moving toward the front -- even a bit unstable. This being a MagLev, there was absolutely no feeling of vibration or wobbling either. I remember feeling the same way during airplane flights but I attributed it to the fact that planes fly a bit tilted upward which in fact means I'm walking uphill as I move toward the front. But the train is completely level and I felt the same thing. I am 100% sure the train was not accelerating as I was near the driver and constantly observed the speedometer. If all objects inside the train are moving at the same speed as the train moving at constant speed and no other forces are exerted upon them as per Newton's 1st Law, I would assume that I would feel no different than being at zero speed. Then why would it feel harder and more unstable to move toward the front of the train?
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1$\begingroup$ 1. The speedometer reads the speed but not the velocity. 2. The train can oscillate up and down slightly. 3. There is acceleration at the curves. $\endgroup$– YashasCommented Mar 6, 2017 at 16:03
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1$\begingroup$ I am convinced that the problem is a brain illusion coming from the discrepency of the informations received through your eyes and your inner ears. $\endgroup$– athenaCommented Mar 6, 2017 at 19:44
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$\begingroup$ Did you feel the same difficulty with the eyes shut? $\endgroup$– athenaCommented Mar 6, 2017 at 19:44
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$\begingroup$ Did you feel that you were walking downhill when moving toward the rear of the train? $\endgroup$– sammy gerbilCommented Mar 7, 2017 at 0:23
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$\begingroup$ I cannot find any corroboration of your observation on the internet. It is pointless to offer scientific explanations for a phenomenon which has not been verified. $\endgroup$– sammy gerbilCommented Mar 7, 2017 at 4:09
3 Answers
I suspect that constant velocity was not actually constant in all three dimensional axes. Even though forward speed might be close to constant, if there is any curvature in the track, deviation from rectilinear motion, the train and its contents can experience cetripetal accelerations.
Also if the train were moving even slightly uphill with any grade other than a straight ramp at constant forward speed there could be vertical accelerations away from the center of the earth creating an effective increase or decrease in gravity. If you were feeling 'heavier' that could account for your difficulty in moving.
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3$\begingroup$ Constant velocity uphill does not increase the effective gravity, just as constant velocity upward in an elevator is undetectable. Only acceleration uphill could increase effective gravity. However, the passenger would actually be walking uphill if the train is pointing uphill, whether it is stationary or moving at constant velocity. $\endgroup$ Commented Mar 7, 2017 at 4:12
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$\begingroup$ @sammygerbil reworded my answer; you are right if the grade is a straight ramp at constant forward speed. But even slight up and down curvature at bullet train speeds could cause subtle, uneasy feeling. Like an elevator. $\endgroup$ Commented Mar 8, 2017 at 1:44
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$\begingroup$ @docscience Based on my inaccurate observations I had thrown out the possibility that it might have been an issue with the velocity vector, but now that I read all your answers I think that might be the case. Like you said, at those speeds, even a small rise or dip would feel significant. And even when I thought I wasn't feeling any vibration or wobble, it just may have been small enough not to feel like a vibration but enough to feel unstable as I walked. Thank you! $\endgroup$ Commented Mar 8, 2017 at 19:11
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$\begingroup$ @docscience ...And also, if the track was curved upward at some point that would explain your "effective" gravity idea since I would be accelerating up. $\endgroup$ Commented Mar 8, 2017 at 19:22
How certain are you that it was level? Did you experiment on a return trip also? Maybe look at the altitudes of each station to find the average slope. If you get the chance take a helium balloon with you and it will show you the direction of the acelleration if there is any present
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$\begingroup$ I was on vacation and didn't bring my instruments with me lol So I'm pretty sure my observations are completely inaccurate. I did feel the same way on the return trip. That's what confused me a bit. But it may very well be that the "uphill" feeling was just my perception being deceived, although im sure that it may just have been frequent undetectable slight variations in direction. $\endgroup$ Commented Mar 8, 2017 at 19:19
It's possible that the train was still swerving slightly side to side or up and down even if it was maintaining constant speed. This would make you feel a little bit unstable as you walk down the aisle.
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$\begingroup$ Yep, that's exactly what I'm beginning to think it was. I disregarded that at first, but its hard to imagine what a small change in direction vector translates to at those speeds. $\endgroup$ Commented Mar 8, 2017 at 19:13