# Hyperloop without acceleration feeling

I have a question about hyperloop. Is it possible to create a hyperloop with high acceleration and that the passengers dont feel the acceleration, theoretically speaking?

And is a situation possible you dont feel acceleration?

• other than a sub-orbital loop: no.
– JEB
Sep 3, 2018 at 23:54

In fact yes it's possible in theory, sorry to disagree with some other posts.

Because of the absence of tidal forces due to earth's gravity on the human scale you don't feel acceleration due to gravity. When you fall you feel a reduction in acceleration against gravity. When in free fall you experience no acceleration although external observers will see you speed up as you follow a gravitational geodesic.

Therefore a frame of reference of vehicle in free fall can be manipulated with artificial acceleration of 1g in any desired direction and the force felt by occupants will be 1g. All you have to do is orient the passenger such that they point in the right direction matching the acceleration and they cannot distinguish this acceleration from that normally experienced on the planet surface. This is Einstein's equivalence principal.

The solution hyperloop involves an initial descent phase and final ascent stage, which are connected by the horizontal transport stage.

In an initial descent and final ascent therefore up to 2g could be applied, which is tons; there are more moderate "partly falling" solutions. Generally the shape has to be very carefully calculated.

I'm not saying it's practical, of course, there are enough engineering challenges in hyperloops already, not least of which is maintaining a tube vacuum in the first place.

• +1 no need to apologise at all, I learnt something. I should have rembered I answered a question a while back on how high a waterslide can be built using same idea. Slightly off topic, the source in my post said something to the effect that the passenger tube would be cramped. It's the same market as Concorde, I was in that (parked) aircraft for 10 mins as a kid, I couldn't believe rich people would pay so much for half the room you get in economy class.
– user140606
Feb 4, 2017 at 0:03
• Hyperloop has many problems to overcome one of which is creating a market need, but I'm at least satisfied that nobody really gave it a serious shot before, unlike supersonic flight. Feb 4, 2017 at 0:07
• although note to arrest any vertical descent either acceleration greater than 1g must be applied did or the path needs to be orbital, including passing through the planet. Did I mention it's not very practical. Feb 4, 2017 at 11:51
• Musk also wants to terraform Mars, using nuclear weapons , it's a "fixer upper of a planet" he reckons, so this hyperloop idea is peanuts compared to that "plan". I asked this question a while back: physics.stackexchange.com/questions/206796/…
– user140606
Feb 4, 2017 at 12:55
• Once your tunnel goes deep enough into the earth, the gravitational field will be lower and that will give you the opportunity to accelerate back towards the surface. It would be interesting to do the math for this - what shape of "tunnel" (starting and ending at the surface of the earth) would give you this constant acceleration? Feb 5, 2017 at 20:15

I guess you want to a roller coaster path with constant apparent gravity (in magnitude). That would be a clothoid loop.

Check the mathematical treatment here.

• While I trust that this is correct, how could you implement this on a hyperloop track? Sure, you'll not feel a "horizontal" acceleration, but by the end of the trip, you will have ended where you have begun, and thus making the hyperloop an expensive merry-go-round. But, I suppose that's a concern for engineers and investors to deal with, not physicists. :) Feb 3, 2017 at 19:04
• @SirJony I don't have an idea applying on the "hyperloop" (as updated with the link). It's hardly without "horizontal" acceleration during the start, but we might allow the car slow down gradually. Feb 3, 2017 at 19:20
• @Countto10 That's my first time hearing about hyperloop (the link updated after my answering) which I thought something relates to roller coaster loop (that's why I said "guess"). I'll keep the post for readers interests (at least for a while). By the way, the commercial name or trademark is out of readers' thoughts about its nature. Feb 3, 2017 at 19:26
• Hi, I think its drifting from physics into engineering, so if you have math, I would absolutely put it in your post. You never know with Musk how serious he is....
– user140606
Feb 3, 2017 at 19:30
• @NgChungTak -- Oh, OK. I guess we were thinking of 2 different hyperloops. :) Feb 3, 2017 at 19:34

First, one should claryfy what it means "to feel acceleration". If you think of that as being pressed into the back of your seat, then yes that can be avoided. Just fill the passenger cabin with a liquid of similar density as your body (e. g. water) and wear some scuba apparatus (the cylinders with pressurized air should be mounted separately, the tubes from the cylinders to your mouth should have a mean density of 1 g cm³) In such a hyperloop you will see pressure rise and fall on a manometer, but no "acceleration" in Your back. A problem might arise with the cavity of your lung, I need to think about that. Georg

• To handle the lung cavity problem, you can use a liquid breathing mixture, like perfluorocarbon with oxygen. Changing the mode of aspiration would take some time, just call it jetlag. That also helps with the initial fear to ride the new system - being anxious of being intubated should mask it. Sep 22, 2018 at 11:01