Can We Spin Air? Spherical Centrifugal Force

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Discussion Overview

The discussion revolves around the feasibility of spinning a sphere of air on its axis, exploring concepts related to centrifugal force, inertia, and the behavior of gases under rotation. Participants consider both theoretical and practical implications, including comparisons to natural phenomena like tornadoes and gas giants.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question whether a sphere of air can be spun, suggesting that while it might be possible in a controlled environment, it may not align with the original intent of the question.
  • One participant argues that centrifugal force acts inappropriately to keep a ball of gas together, noting that gravitational forces are necessary for larger bodies like stars.
  • Another viewpoint suggests that while spinning a solid object like ice is feasible, spinning air or water would result in the molecules moving off in straight lines due to inertia.
  • Some participants mention that gas planets like Jupiter and Saturn are examples of large bodies of spinning gas, though they acknowledge the complexities involved in achieving similar conditions artificially.
  • There is a proposal to create a laminar flow of air in circular motion, but concerns are raised about the feasibility of maintaining such a flow without significant energy loss due to friction.
  • One participant suggests that spinning a disc of ice in space and subsequently heating it could lead to a self-spinning disc of water, but others challenge this idea based on the behavior of liquids and gases under rotation.
  • Discussions also touch on the nature of tornadoes and vortices as examples of spinning air, with some participants expressing skepticism about the possibility of achieving a stable spinning sphere of air.

Areas of Agreement / Disagreement

Participants express a range of opinions, with no consensus reached on the feasibility of spinning a sphere of air. Multiple competing views remain, particularly regarding the roles of inertia, gravity, and the nature of gases versus solids.

Contextual Notes

Limitations include the dependence on definitions of "spinning" and "sphere," as well as the unresolved nature of the forces required to maintain a spinning volume of air. The discussion also highlights the complexities of achieving laminar flow and the effects of temperature and pressure differentials.

1832vin
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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
 
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In a carefully controlled test environment you might get something close, but I don't think it would be quite what you're imagining.
 
"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.
 
1832vin said:
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
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.
 
1832vin said:
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

Narutard?
Yes, it is possible. Its called the atmosphere...
:-p
 
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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.
 
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.
 
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!
 
1832vin said:
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!

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.
 
  • #10
gabriel.dac said:
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.

So this shouldn't be possible, right?
https://www.youtube.com/watch?v=BxyfiBGCwhQ
 
  • #11
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.
 
  • #12
Enigman said:
So this shouldn't be possible, right?
https://www.youtube.com/watch?v=BxyfiBGCwhQ

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
 
  • #13
gabriel.dac said:
rotate it faster and see if it will still be that way.

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

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.

makes no sense in the context of the thread.
 
  • #14
tornadoes, hurricanes, vortices
 
  • #15
1832vin said:
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?
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.

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

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!
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?
 

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