An old one I posted years ago: helium balloon

Originally posted by AThousandYoung
How would you make a balloon with perfect bouyance i.e. ignores gravity but doesn't rise either?

Could you have a mixture of gases so it essentially floats?
I remember messing around with balloons at one of my old jobs mixing it with part my breath and part helium and it sunk very very slowly, always tried to get the thing to float.

Originally posted by ua41
Could you have a mixture of gases so it essentially floats?
I remember messing around with balloons at one of my old jobs mixing it with part my breath and part helium and it sunk very very slowly, always tried to get the thing to float.

Yeah, that should work. Get a ratio of CO2 from breath and He such that it levitates.

Originally posted by AThousandYoung
Here's something to think about. Besides H2 and He, what kind of gases would be bouyant in a balloon on Earth? What would the characteristics of the balloon be (e.g. H2 burns)?

How would you make a balloon with perfect bouyance i.e. ignores gravity but doesn't rise either?

I did that for my kids a long time ago. Take a party He balloon, it has a string attached, it rises if you let go, goes to the ceiling. But tie enough stuff to the string and you find a point where it sinks instead. Then take off some mass, little bit at a time, and eventually you get to a point where the balloon just sits there in midair. The balloon will, however, follow any convection currents in the room and if there is a temperature difference from the floor to the ceiling, it may expand a bit which will cause it to rise, so you have to keep playing with the mass on the string.

I also was able to make it sink by cooling it down and to rise again by shining a radiant electric heater on it, the He expands and then it starts to rise. But if the air is somewhat cooler, the heat will dissipate causing the He to contract and the balloon to sink again. I got it to go up and down that way, never touching it, just heating it with the radiant heater, turning it off, it rises, stays up for a while, comes back down, then re-heating, etc.