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How fast can a human safley accelerate?

  1. Mar 21, 2012 #1
    In a straight line, on sea level (if it matters), how fast can a human safley accelerate? Not just the strongest human, but even the weakest, like an elderly or a child. Assume that they are strapped in a seat.

    I'm thinking about those maglev trains in air evacuated tunnels and how fast they could actually reach 8000KM/h, as some suggests is possible, without harming anyone.
     
  2. jcsd
  3. Mar 21, 2012 #2
    apparently this guy survived some 46Gs of acceleration.

    http://www.pbs.org/wgbh/nova/space/gravity-forces.html

    I'm not sure if the human body cares much about the orientation of the acceleration with respect to the direction of earth's gravity at that high an acceleration, because gravity in that case is only a small component of the total acceleration vector.
     
  4. Mar 21, 2012 #3
    Well ok, thanks, but it didn't really answer my question.
     
  5. Mar 21, 2012 #4
    oops, didn't read your question carefully.
    I would imagine the safe acceleration for general public would be similar to that designed for commercial aircraft.
    http://www.airliners.net/aviation-forums/tech_ops/read.main/17454/
    lists thrust to weight ratios, which should allow one to figure out accelration with some assumption on the weight of a beoing 777...
     
  6. Mar 21, 2012 #5
    8 minutes of 1/2 g acceleration would get the train to speed with minimal effect on humans. That would be the same force acting on the body as a continuous 15 degree banked turn in an airplane and that's hardly noticable.
     
  7. Mar 21, 2012 #6

    rcgldr

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    The space shuttle limited sustained (several minutes) acceleration to 3g's, and a few of the astronauts were fairly old, or civilians. Some roller coasters pull higher g's than this for shorter periods of time, but that is downwards which is worse since it tends to drain blood from the brain.
     
  8. Mar 21, 2012 #7

    A.T.

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  9. Mar 21, 2012 #8

    sophiecentaur

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    g forces will have different effects on different occasions. A fighter pilot, pulling out of a dive would pass out if it were not for the g suit he wears. This is a glorified pair of tight trousers, which prevent the blood from going down into his legs as his body is forced upwards.
    Incidentally, those giant 'swing boat' rides at the funfair give you 3g at the bottom if they start off with the support arm horizontal. This is irrespective of the radius of the arm.
    Passenger aircraft pull about 1g as they accelerate along the runway.
     
  10. Mar 21, 2012 #9
    Yes, but I think my question was pretty specific.. =p
     
  11. Mar 21, 2012 #10

    sophiecentaur

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    Yes it was. But the word "anyone" leaves it a bit open.
     
  12. Mar 21, 2012 #11
    i see, so i guess in your particular case of accelerating perpendicular to the direction of upright sitting person you wouldn't worry too much about draining blood from the brain. but have to worry about breaking rib cages tho.

    maybe figure out strength of human bone, multiply that number by 2/3 to account for aging for infancy, and divide that force by an average human mass to figure out that acceleration that's safe for a rib cage?
     
  13. Mar 21, 2012 #12

    Filip Larsen

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    Without being able to cite a specific reference, I believe that the maximum horizontal acceleration that will maintain passenger comfort in railroad carriages is in the order of 1-3 m/s2, with 1 m/s2 being perceived as "firm acceleration" and 3 m/s2 being perceived as "hard breaking". If passengers are strapped-in and seated in seats that "supports" heavy horizontal acceleration (like in airplane seats during takeoff and landing) it may be (my guess) that it will be possible to use higher acceleration without significant loss of comfort. Also note that passenger comfort for a particular acceleration profile in general depends not only on the "maximum" value but also on the vibration spectrum. A completely smooth acceleration profile (that is, one with no perceptible vibration) will probably be able to "achieve" the same passenger comfort at a higher maximum acceleration that if significant vibration is present.
     
  14. Mar 21, 2012 #13

    Ryan_m_b

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  15. Mar 21, 2012 #14
    Vertically, yes; horizontally, no. Typical would be around 1/3 g.
     
    Last edited: Mar 21, 2012
  16. Mar 21, 2012 #15
    1/10 g is considered detectable but just.
     
  17. Mar 21, 2012 #16
    Has the original poster specified tranverse or longitudinal G loading?
     
  18. Mar 21, 2012 #17

    Filip Larsen

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    The word "firm" was a somewhat loose interpretation on my part. I've seen figures around 1 m/s2 (or 1/10 g as you say) being quoted as the comfort acceleration limit for train passengers; presumably this limit (when applied smoothly) will still allow old ladies to walk down the aisle without too much trouble as the apparent incline only is around 6 deg.
     
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