Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can we spin air?

  1. Nov 20, 2013 #1
    can we spin a shpere of air? not the shell only, but the whole volume itself spinning on it's axis, can we do that and let a ball of air spin with momentum, and if it is fast enough, it would form such a centrifugal force that it can maintain itself without keeping on spinning it
     
  2. jcsd
  3. Nov 20, 2013 #2

    Drakkith

    User Avatar

    Staff: Mentor

    In a carefully controlled test environment you might get something close, but I don't think it would be quite what you're imagining.
     
  4. Nov 20, 2013 #3

    AlephZero

    User Avatar
    Science Advisor
    Homework Helper

    "Centrifugal force" is acting the wrong way to keep the ball together.

    This definitely works for a ball of gas the size of the sun, but that probably wasn't what you had in mind. What keeps it together is the fact that the gravitational force is stronger than the forces trying to pull it apart.
     
  5. Nov 21, 2013 #4

    NascentOxygen

    User Avatar

    Staff: Mentor

    It is an interesting idea to ponder. But momentum of each molecule would see it moving off in a straight line. If you want it to turn, what force would be acting on each molecule to stop it moving off in a straight line?

    You could try it with a drop of water, spinning and suspended (somehow) in air. But if the layers are not to slide over each other (and quickly dissipate energy in viscous friction) then each layer needs to be acted on by a different magnitude force to make it appear that the whole lot is rotating as a block. Again, not feasible.

    A sphere of solid material is a better proposition! That is, until you have it spinning so fast that it's unable to sustain the internal forces between layers and it rips apart.
     
  6. Nov 21, 2013 #5
    Narutard?
    Yes, it is possible. Its called the atmosphere...
    :tongue:
     
    Last edited: Nov 21, 2013
  7. Nov 21, 2013 #6

    etudiant

    User Avatar
    Gold Member

    Not so sure about a sphere, but you can often see videos of spinning cylinders of air on the news.
    Spinning a sphere though would be a lot harder to achieve, the best approximation I can think of would be a short, fat tornado.
     
  8. Nov 21, 2013 #7
    Jupiter, Saturn, Uranus and Neptune are spinning right now, and they are "air".

    I know that in the center of those planets there must be liquids because of the pressure, but that is just a consequence of a great gravitational field.
     
  9. Nov 21, 2013 #8
    i was thinking "all mass has gravity" and planet earth has air spinning itself without breaking a sphere... so i thought, can we make a laminar flow of air in a circular motion? then if we can do it fast enough, we can have a high compressed layer of air on the surface and inside of the spinning,
    well... something like making earth in earth,
    i was thinking could we first try to have a discus of ice, spin it in space (high speed) and then heat it up through radiation then we get a discus of self spinning water!
     
  10. Nov 21, 2013 #9
    No. There is a thing called inertia. A block of ice will spin because it is solid. Water or air will just travel at a straight line forever.

    In my opinion the only way you can spin air is by making a gas planet and make it rotate.
     
  11. Nov 21, 2013 #10
    So this shouldn't be possible, right?
    https://www.youtube.com/watch?v=BxyfiBGCwhQ
     
  12. Nov 21, 2013 #11

    etudiant

    User Avatar
    Gold Member

    We need to define what we are considering.
    The OP was surely not thinking of a planet sized envelope of air when he asked 'can we spin a sphere of air'?
    For a small volume, where gravity is a non issue and even temperature and pressure differentials are small, the answer is clearly no, at least imho.
     
  13. Nov 21, 2013 #12
    rotate it faster and see if it will still be that way.

    Anyway.... ok. Water is a little "sticky", so it can form a bubble. But I'm pretty sure that there is no way you can do that with any gas
     
  14. Nov 22, 2013 #13

    Borek

    User Avatar

    Staff: Mentor

    Anything rotating fast enough will break, so it is a non-argument. Your earlier comment:

    makes no sense in the context of the thread.
     
  15. Nov 22, 2013 #14
    tornadoes, hurricanes, vortices
     
  16. Nov 22, 2013 #15

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    The flow is unlikely to be laminar... if you are relying on gravity to provide the centripetal force, then you need rather a lot of "air". Regular room temp is enough to stop small volumes from being gravitationally bound.

    Its the other way up... You get the high pressure lower down.
    But see, for instance, Larry Niven's "Smoke Ring".

    Water forms globules in free fall and spinning a globule will flatten it out. There's probably video of an astronaught doing just that.

    There are lots of ways to get a bunch of gas to spin.
    Self sustaining the spin is harder.
    But the devil is in the details... what do you want to achieve?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook