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"I'm surprised at how many groups are still using He (a VERY limited and nonrenewable resource) instead of the more buoyant H2 alternative."

Chuck, it sounds like you creeped up on, but didn't quite directly state a very common misconception about the lifting power of hydrogen and helium. Many people think that because hydrogen has half the mass (and therefore half the density) of helium, that it will have twice the lifting power. But that's not how lifting power (or buoyant force) works.

The lifting power of a gas confined inside of a balloon is the difference between the mass of the gas and the mass of an equal volume of air (minus the mass of the balloon). So, if we assume exactly a 22.4L balloon at standard temperature and pressure (i.e. one mole of gas), hydrogen has a mass of 2.0 grams, helium has a mass of 4.0 grams, and air (approximately) 28.8 grams. So the lifting power of a hydrogen-filled balloon of this size would be 26.8 grams and the lifting power of a helium-filled balloon would be 24.8 grams. That's only an 8% increase. It's probably not worth the additional cost and danger. A 10% larger helium balloon would be far cheaper and safer.

I can't comment on the renewability. I doubt that it really went out of the atmosphere, it would have exploded long before that. So, the helium is probably still in the atmosphere somewhere.

I have an episode of my Science Misconception Podcast on this topic at http://scienceinquirer.wikispaces.com.

Mike

----- Original Message ----- From: "chuck britton" <cvbritton@mac.com>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>; <tap-l@lists.ncsu.edu>
Sent: Tuesday, October 19, 2010 12:30 PM

As someone else has already noted - there's a lot of this going on these days.
FAA regs allow for lightweight packages with no rigamarole (sp?)

I'm surprised at how many groups are still using He (a VERY limited
and nonrenewable resource) instead of the more buoyant H2 alternative.
.
At 7:11 AM -0400 10/19/10, Anthony Lapinski wrote:
A colleague just sent me this 7-minute video clip of a balloon with a
camera attached that went up into space. The balloon later expanded,
exploded, and the camera went into free fall. Very interesting! Very cool!

http://vimeo.com/15091562

Might be a good project for students?
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