UCSB Science Line
Sponge Spicules Nerve Cells Galaxy Abalone Shell Nickel Succinate X-ray Lens Lupine
UCSB Science Line
How it Works
Ask a Question
Search Topics
Our Scientists
Science Links
Contact Information
What happens on a molecular level inside a balloon as it inflates?
Question Date: 2014-12-08
Answer 1:

Thank you for your question! As a balloon inflates, the air pressure (or helium pressure) inside the balloon changes. It can be theoretically and experimentally shown that the pressure increases until the balloon radius is about 1.4x the uninflated radius. Above that point, the pressure continually decreases until eventually the balloon pops. The wikipedia article on the "Two-balloon experiment" shows this. It's very interesting!

Let's assume the balloon is inflated at constant temperature. Using the ideal gas law, we can see the that density of air molecules (N/V) is directly proportional to the air pressure. This means that as the pressure increases, the air molecules are closer to each other, and attract each other more strongly due to van der Waals interactions. Because the pressure inside the balloon is typically not very large (about 1% greater than atmospheric), these van der Waals interactions are mostly unaffected during inflation. Thus, the largest difference molecularly is simply the density of air (or helium) molecules.


Click Here to return to the search form.

University of California, Santa Barbara Materials Research Laboratory National Science Foundation
This program is co-sponsored by the National Science Foundation and UCSB School-University Partnerships
Copyright © 2020 The Regents of the University of California,
All Rights Reserved.
UCSB Terms of Use