MadSci Network: Chemistry

Re: Would putting Helium in shoes make any differnece?

Date: Wed Oct 20 14:13:57 1999
Posted By: Jeremy Starr, Grad Student, Chemistry, California Institute of Technology
Area of science: Chemistry
ID: 939944108.Ch

Yes (technically) and no (let's be realistic).


Let's assume there is about 100ml of sealable space in the sole of the 
shoe. (I think this is generous). The atomic weight of helium is 2g/mole 
or about 2g/22.4 liters of space. The air that would have been occupying 
that space is about 20% oxygen (32g/mole) and 80% nitrogen (28g/mole) 
giving a weighted average molecular weight for air of 28.8g/mole or 
28.8g/22.4 liters of space. The difference in weight of the shoe would 
then be (28.8g - 2g)*(100/22400)= 0.12g

One could expect the helium shoe to weigh 0.12g less than the otherwise 
identical air filled shoe.  


The 0.12g difference is probably much less than the average variation in 
mass from one "identical" shoe to the next and it certainly is well within 
the variations in body weight and clothing weight one experiences on a day 
to day basis. Therefore the only observable weight difference between the 
helium shoes and other shoes will be in your wallet (a dollar bill weighs 
1.0g... you can do the math!).

Happy shopping!

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