# Why do Balloons filled with Air not fall at 9.6m/s/s?

1. Sep 8, 2009

### Salbris

I've been racking my brain to figure this one out, I really don't understand it.

If you fill a balloon with air from your lungs, just manually blow it up, it should be carbon dioxide, no?

Density of Carbon Dioxide at Sea Level: 1.977 g/L
Density of Air at Sea Level: 1.2 g/L

So it's heavier. I know I'm pulling these numbers out of seemingly nowhere, but I'm sure someone can verify they are accurate.

So why on Earth would a balloon filled with a gas heavier than the surrounding gas in it's environment not drop at the normal speed. Aren't I right to think that bouyancy only takes effect when the gas inside the balloon is at least a bit lighter?

Or is there some critical property I'm missing?

2. Sep 8, 2009

### Bob S

Do you recall that Gallileo dropped a feather off the Tower of Pisa, as well as a 1 pound weight and a ten pound weight:
http://www.jimloy.com/physics/galileo.htm [Broken]
Astronauts tried Gallileo's experiment on the moon. See:

Last edited by a moderator: May 4, 2017
3. Sep 8, 2009

If you fill a balloon up with your breath it would be mostly nitrogen just like the air you breathed in.

Also, with a density so close to that of the air it is prone to the slightest disturbances from the air.

4. Sep 9, 2009

### DaveC426913

1] As pointed out, your exhaled breath is almost exactly the same as the air. It has an extra 5% CO2 and is shy by the same amount of oxygen.

2] You've got a volume of air, that weighs maybe a gram or two more than the surrounding air, but it has a giant surface area. It's terminal velocity is on the order of a few feet per second.

5. Sep 9, 2009

### Salbris

Ahh, Terminal Velocity. Now that makes sense. :)

Thanks for pointing that out.