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Post Reply What stops the can from floating away?
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Posted 3/17/16

DeadlyOats wrote:

Helium is lighter than air because it is a smaller, lighter molecule than the other air molecules, and because when helium fills a volume, it takes up more space, meaning there's more space between helium molecules. This is why a helium filled balloon will rise, and why helium is constantly seeping out of the ground, floating all the way up to the edge of space and getting blown away by the solar winds.


Similarly, there are heavier-than-air gases, like Sulfur hexaflouride, which will sink below a level of normal oxygen air:
https://www.youtube.com/watch?v=A7XdOyZIkko
Posted 3/19/16

DeadlyOats wrote:

Helium is lighter than air because it is a smaller, lighter molecule than the other air molecules, and because when helium fills a volume, it takes up more space, meaning there's more space between helium molecules. This is why a helium filled balloon will rise, and why helium is constantly seeping out of the ground, floating all the way up to the edge of space and getting blown away by the solar winds.

However, the helium in the can is compressed, the helium molecules are densely packed. There is very little space between the molecules, as such it would be heavier than the surrounding air molecules as a whole. It doesn't help that the can is made of metal, but let's say that you could compress the same number of helium molecules (in a given volume within the can) into a balloon (with the same given volume) - without it stretching and popping. That helium balloon would not float. However, as soon as the helium molecules are allowed to expand and take up all the space they want, that balloon will expand greatly, and then rise. This is because the density of the helium molecules will become much less than the density of the air outside of the balloon.....

I typed more than I wanted to...


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