# Helium balloon in zero gravity

1. Sep 24, 2004

### relativelyslow

a couple nights ago whilst my presleep thoughts wondered about, i came across a balloon filled with helium. in this thought, i saw the not uncommon sight of it floating up. then i wondered why it went up and not down or some arbitrary direction. i know helium is lighter than our oxygenic atmosphere, so it rises. to explain this, i figured that gravity must pull the heavier substance downward with more force, so the helium struggles to get out of the oxygen, as water poured into vegetable oil sinks. so, as my thoughts progressed, what would happen if there was no gravity? my hypothesis is, if a helium balloon is placed in an oxygen environment that has no gravity, as in space inside a spaceshuttle, it will stay still, not rising or sinking. what further leads me to think this true is the contemplation of which way it would rise, for, without gravity, which way is up? does anyone else agree with this?

2. Sep 24, 2004

### kawikdx225

Agreed, the oxygen isn't trying to push the balloon in any particular direction, assuming no "wind". If you waved your hand in front of the balloon you would cause oxygen to bounce into the balloon sending it in motion.

3. Sep 25, 2004

### relativelyslow

is helium less dense than oxygen (our atmosphere/the space shuttles supply)? if it is, would anything happen due to the difference in pressure? the only thing i can think of is the balloon shrinking once in zero gravity (or would it expand?).

4. Sep 25, 2004

### GOD__AM

Yes helium is less dense than air at equal pressure. Air is mostly nitrogen (79%) though, and only about 1/5 oxygen (20.9%).

In relativly equal pressure and tempature, the size of the balloon should remain the same. In the shuttle the cabin is pressurized to close to earth pressures and air mixture. If the baloon was let go into the vacuum of space it would probabally expand until it burst, letting the helium escape rather quickly. This wouldn't have anything to do with the gravitational field though. The same thing would happen here on earth if we put the balloon in a sufficently large container and sucked out the air.

To answer the first part of your question if you place the balloon anywhere in the cabin of the space shuttle it would remain exactally where it is indefinatly. However as stated the air moving around the inside of the shuttle would soon have the baloon moving about. I think you were right to assume that it would not rise, fall,etc...

5. Sep 25, 2004

### kawikdx225

The shape of the balloon will change with\without gravity but the size is determined by the pressure difference.
I'm not sure what the pressure inside the space shuttle is but as long as it's constant the balloon size will remain constant.
If the captain decided to increase cabin pressure then the balloon would shrink.
If you flushed the balloon into the vacuum of space it would expand/pop.

6. Sep 25, 2004

### kawikdx225

lol, God was too fast for me.

7. Sep 27, 2004

### relativelyslow

ah excellent. i guess that puts that to rest. im not sure i can think of any more questions pertinent to this. thanks.