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I was reading things about the Hyperloop One start-up project ( https://hyperloop-one.com/what-is-hyperloop) and I couldn't get any details on how the process works. This is a new transportation type which is being currently tested & studied.

Basically, they say it's a huge pipe network where the air pressure is greatly reduced. And via eletric rotors, a kind of giant capsule is propelled through this pipe.

My question is, how can the fact of reducing pressure can affect speed ?

Thanks for your englightenment I'm confused and I don't know what to search to have this information :)

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  • $\begingroup$ Of course the speeds will not be the same. Thats aerodynamics. You cant move as fast in water as you can through air can you? Same here. $\endgroup$
    – Lelouch
    Commented Jul 6, 2016 at 10:52
  • $\begingroup$ @Lelouch forgive my silly question, actually I knew it work (I didn't intended to write the feather comparison in my message) but what I wanted to know is "why". M. Enns summed it up quite clearly. $\endgroup$
    – Alex
    Commented Jul 6, 2016 at 11:37

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No, a feather dropped in a vacuum jar will not drop at the same speed as in air. There must be a thousand video's out there of this very topic but my favourite is this one.

An object moving through air, or any fluid, will experience a drag force resisting its motion. This force increases as the speed of the object through the fluid increases. It also increases with the density of the air. Lower air pressure means less drag force. For a falling feather this would mean a larger terminal speed. For a train in a tube this would mean less force required to drive the train at a given speed.

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  • $\begingroup$ Thanks, so this is playing with drag forces ! About the feather comparison, just forgot it, I wrote that with empty mind, I knew it was the case ahah $\endgroup$
    – Alex
    Commented Jul 6, 2016 at 11:38

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