1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Human capacity for G-forces, Energy calculation, and thrust

  1. Mar 5, 2015 #1
    I hope this is the right place for this...

    Question #1. How much can the human body stand multiple rapid G-force changes. Like let's say I made a vehicle that you could make sure all your body parts were 100% secured and it could move freely in space in any direction what would be the result of changing X amount of acceleration over and over again. I'm basically looking for the maximum amount of movement velocity changes a jet in space could do and still be relatively safe. I know fighter jet pilots can withstand up to 9g for a few seconds and normal humans can survive 6gs for a few minutes without problem, but this tells me nothing really of if I were to keep changing my velocity how safe that would be. Like if I went 6g to the right and then 6g to the left 1 second later and kept doing that how much could a human stand of that? Obviously we can stand some level of this and it changes for which direct the force is applied, but does anyone have any clue about this?

    Question #2. Let's say i have the same jet described above. How would I calculate the energy needed to be able to operate for 24 hours assuming that I wanted to be able to perform any maneuver, full stop, rotational etc as much as I wanted over that 24 hour period? Would I just calculate 3x the energy for the maximum thrust I want? I assume that you need the energy to thrust 1 way, the same amount of energy to stop, and then the same amount of energy again to go the opposite way, which makes 3x the energy, and I also assume that any rotational thrust to go and stop would be less than the energy for the translational thrust so that all rotational thrust energy needed would fall within the translational thrust energy calc, but I don't know, would you count translation and rotational energy as separate maneuvering possibility and thus need more energy, or perhaps are all axis different energy numbers because you could move in all three at once meaning that the energy requirements would be 3x energy for left right, 3x for up down, 3x for back forward, ?x for horizontal rotation, and ?x for vertical rotation?

    Question #3. I know generally how a jet works, however, I don't know how materials existing one side effects velocity. What I need to know is you were to take air and put it in a tank in a vacuum that is otherwise a vacuum inside with one side having a hole what is going to change the thrust of that air is going to have? Is it simply the speed at which the air leaves the tank?

    Let's say I have 100 oxygen atoms in the tank. And I can change the speed of the atoms leaving the tank from 1 to 10.
    If I throw an atom out at speed of 1 and it imparts 1 thrust will 2 atoms of oxygen impart 2 thrust?
    If I throw an atom out at speed of 2 will that impart 2 thrust?
    If I throw all 100 atoms out at once will that impart 100 thrust?
    Or would throwing out 1 atom at a time 1 after the other create more thrust?
    Or is it both and these need to be balanced against each other?

    Hopefully I've been clear in what I'm asking.
  2. jcsd
  3. Mar 5, 2015 #2


    User Avatar
    Science Advisor

    What does this mean? How are they supported? When floating in a liquid, and using liquid ventilation mice can stand 3800g for 15min "without any physical impairment" (no loss ofconsciousness etc.):

    What you are asking about is the change of acceleration (jerk), which is much harder to withstand than just a constant high acceleration, because the body has to dissipate lots of energy.
  4. Mar 5, 2015 #3
    What I meant is basically they were strapped down so that their body isn't going to lean forward and then come back, but their internal organs are free to move around as normal. Basically, they're not going to be tossed around from this movement so they won't go splat against a wall lol.

    I did not consider what to change g survival ability, but, from a brief scan of that pdf, it seems that even though it interesting application isn't worth considering currently. Though, thanks for the information. It may prove helpful in the future.

    I guess. I'm not sure as I am aware of the term, but not its correct usage. Reading on to question 2 you can see that question 1 is important to answer to get my overall answer for question 2, which is more important to me than is question 1 itself.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook