Ask A Scientist Materials Science Archive

name Rigela
status educator
grade 9-12
location N/A

Question - What are some simple experiments involving diffusion which
explore the theories and concepts surrounding the surface area to volume 
ratio?
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This took some thought. I don't know the answer to the proposed
experiments. Fill various size balloons rubber -- not aluminized -- with
helium gas. You can measure the internal pressure with a simple pressure
gauge, the volume (assume a sphere so: V= 4/3*pi*R^3 and surface area S=
4*pi*R^2. Then follow the decrease in volume and surface area as the
helium diffuses through the rubber. It only takes a few days. The pressure
can be related to the volume and surface area by monitoring the pressure
as you blow the balloons up. You can determine "V" and "S" by measuring
the circumference of the balloon C= 2*pi*R vs. time. This gives you "V",
"S", and "P" as a function of time, size and pressure. Use different size
baloons.

Vince Calder
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