# Another helium balloon puzzle:

sonhouse
Posers and Puzzles 08 Jan '06 16:43
1. sonhouse
Fast and Curious
08 Jan '06 16:43
you have a centrifuge big enough to hold a 10 foot long cylinder
about 3 feet in diameter. It is filled with standard Atm. You place a
helium balloon in the center of said cylinder and start it spinning,
What happens to the balloon?
2. Wibble Wobble
Action barbie
08 Jan '06 17:05
Originally posted by sonhouse
you have a centrifuge big enough to hold a 10 foot long cylinder
about 3 feet in diameter. It is filled with standard Atm. You place a
helium balloon in the center of said cylinder and start it spinning,
What happens to the balloon?
Spins?
3. sonhouse
Fast and Curious
08 Jan '06 22:19
Originally posted by Wibble Wobble
Spins?
I'll give you that, but does it move anywhere else?
4. 08 Jan '06 22:36
Originally posted by sonhouse
I'll give you that, but does it move anywhere else?
moves toward wall
5. sonhouse
Fast and Curious
08 Jan '06 23:28
Originally posted by ketch90
moves toward wall
Expand on That. What wall? The wall of the spinning cylinder?
Also you know the whole cylinder is spinning as if on a rope, in this
case the boom, so it has to be counterbalanced completely on
the other side, its not spinning around its own center.
6. 09 Jan '06 01:05
ok: base is resting on x-y plane. is it spinning around the z-axis or the x/y-axis?
7. 09 Jan '06 02:14
Originally posted by sonhouse
you have a centrifuge big enough to hold a 10 foot long cylinder
about 3 feet in diameter. It is filled with standard Atm. You place a
helium balloon in the center of said cylinder and start it spinning,
What happens to the balloon?
Is it a Mickey Mouse balloon, with ears on it? This is important in my calculations.
8. 09 Jan '06 11:291 edit
I would have thought it would start spinning due to air currents in the cylinder causing it to spin. The balloon could then move in any direction due to chaotic effects. Once it hits any wall it would then be forced to one of the ends by centrifugal force.

Edit: The balloon will expand slightly as well while in the centre, because the centrifugal force would cause some of the air to also move towards the ends reducing the pressure in the centre.
9. 09 Jan '06 19:26
Edit: The balloon will expand slightly as well while in the centre, because the centrifugal force would cause some of the air to also move towards the ends reducing the pressure in the centre.[/b]
there is not really any such thing as centrifugal force.
does the baloon stay still in relation to outside of the cylinder, but spin in relation to the inside of the cylinder?
10. 09 Jan '06 22:46
Originally posted by i am scientists
there is not really any such thing as centrifugal force.
Well, there is an opposite reaction (this can be called centrifugal force) to the centripetal force which is a force directed towards the centre of axis of rotation. This opposite reaction is more easily apparent though. I was just being conservative with my choice of words. ðŸ™‚
11. sonhouse
Fast and Curious
09 Jan '06 22:58
Originally posted by i am scientists
there is not really any such thing as centrifugal force.
does the baloon stay still in relation to outside of the cylinder, but spin in relation to the inside of the cylinder?
I think I said the cylinder is not spinning on its axis, either one.
Its hanging totally out and spun in total around like the big arm of
the flight G simulators, picture that arm as containing said cylinder.
It would be a lot better with a drawing for sure.
So under those conditions, say its giving the equivalent of one G
of force, what happens to the balloon?
12. 09 Jan '06 23:511 edit
Originally posted by sonhouse
I think I said the cylinder is not spinning on its axis, either one.
Its hanging totally out and spun in total around like the big arm of
the flight G simulators, picture that arm as containing said cylinder.
It would be a lot better with a drawing for sure.
So under those conditions, say its giving the equivalent of one G
of force, what happens to the balloon?
Think I know what you are describing. The balloon would actually move towards the axis of rotation. The air would increase in pressure at the end of the cylinder (end as in direction away from the axis of rotation). The balloon would oppose this force due to gas bouyancy (tend towards the axis of rotation where the air density would be less). This is because of the low gas density of the helium in the balloon.

I think this is correct. ðŸ™‚

Edit: Based on the original idea I thought you had where the cylinder was actually rotating in my previous post. The balloon would stay in the centre because that is where the air density will be least, not go towards one of the ends as I previously described. Not related to the current scenario in this thread but still a point I needed to correct. ðŸ˜€
13. sonhouse
Fast and Curious
11 Jan '06 06:27
Originally posted by lausey
Think I know what you are describing. The balloon would actually move towards the axis of rotation. The air would increase in pressure at the end of the cylinder (end as in direction away from the axis of rotation). The balloon would oppose this force due to gas bouyancy (tend towards the axis of rotation where the air density would be less). This is because ...[text shortened]... d. Not related to the current scenario in this thread but still a point I needed to correct. ðŸ˜€
Give the man the golden ring! Thats what would happen. I told this
one to my son Kevin and he had the answer before I could even
finish telling it. He is used to my puzzles by now.
I had one where the same kind of cylinder was on a space ship
way away from stuff so basically at zero gravity and then you do the
same thing, put a balloon dead center, then fire a rocket at one end.
What happens to the balloon? Same thing, If it were a bowling ball
it would go to the end where the rocket is of course but a helium
balloon goes the other way for just the reason you said:
pressure differential is what gives the lifting force so I was pointing
out what Einstein said a long time ago: you can't tell the differance
between gravitation and acceleration so if you take the cylinder and
just hold it upright, gravity does the pressure gradient, if you spin it,
centripital does it, if you fire up a rocket, acceleration does it.
All three ways end up with a pressure gradient. I think I have run this
one into the ground!
14. 11 Jan '06 17:47
Originally posted by i am scientists
there is not really any such thing as centrifugal force.
In the cylinder's frame of reference, there is.
15. Trains44
Full speed locomotiv
11 Jan '06 17:49
Originally posted by sonhouse
you have a centrifuge big enough to hold a 10 foot long cylinder
about 3 feet in diameter. It is filled with standard Atm. You place a
helium balloon in the center of said cylinder and start it spinning,
What happens to the balloon?
Probably get dizzy. No?