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morsch

Vertical acceleration refers to acceleration in the direction of the tracks, right?

Some other figures I could find:

Shinkansen: 2.6 km/h/s = 0.07g

ICE (German HSR): 0.5 m/s2 = 0.05g

S-Bahn (metro transport): 1 m/s2 = 0.1g

Makes sense that metro transport has higher acceleration, as high speed rail spends a lot of time "cruising" at certain speeds, while metro transport is basically always either accelerating or decelerating. I'd guess subways also feature relatively high g-forces.

Also interesting: http://en.wikipedia.org/wiki/Orders_of_magnitude_%28accelera...

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I'm think vertical means bumps and dips, for which we really have little tolerance. I don't see i being much of an issue for hyperloop, as varying height of the pillars is pretty easy...

My understanding of his/her comment was that vertical acceleration is "up & down" (perpendicular to the earth).

I believe specifically, perpendicular to the passenger's horizontal reference frame.

Are you saying that laying down on a roller coaster would make it less nauseating?

Admittedly I have not tried it but I don't think that would work.

It would, but not for the reason you think: lying on your back activates the mechanism you still have from when you were a baby that stopped you getting motion sickness when you were being carried by your mother. We advise people suffering from seasickness that one thing they can do is lie on their backs, and it often is enough by itself.

That would also be one reason why motion sickness in microgravity is so pernicious.

Vertical as in up-down. You're much more comfortable accelerating forwards-backwards or left-right.

Then change the orientation of the seats? Without a reference frame you can't tell.

Gravity?

Include that in the calculations. There's a certain absolute sideways g-force (decreasable by slowing or straightening), and a certain absolute downwards gravity. These add up to a single total force. So long as the magnitude is at least 1g, there exists a seat orientation such that the passenger feels 1g toward the seat and something on the back.

How much you can spin the seat without those movements causing problems is an open question.

Airplanes are an encouraging precedent. They often make quite sharp turns at extremely high velocity, but tilt into them such that there's almost no perceived lateral acceleration.

You'd still be going up (from the Earth's surface) and down (towards the Earth)...

Is there a source for left/right acceleration being more comfortable than down? My subjective/uneducated guess would actually be that acceleration is most comfortable in the order of: forwards, up, backwards, left/right, down.

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