## Kubic Bubbles

Author(s): Denise Agapoff & Stacie Bailey

SED 695B
Advanced Laboratory Curriculum Developement

Principles illustrated:
* symmetry
*shortest distance between two points
*minimum surface area
*Helmholtz free energy

9a&b. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations.

Materials
Explanation of principles involved

*two 13cm x 13cm plexiglass plates
*four rubber suckers
*bubble solution

A soapy film has the property that its surface area has a minimum value when it has reached equilibrium.
This is the result of minimizing Helmholtz free energy. Helmholtz free energy in the internal energy of a system which is based on the internal energy, entropy and temperature of the system. The Helmholtz free energy is a measure of the amount of energy you have to put in to create a system once the spontaneous energy transfer to the sytem from the environment is accounted for.

Procedure:
* pour bubble solution into a shallow pan large enough to accomodate the plexiglass plates
*place rubber suckers in desired position (triangle, square, etc)
* dip the plates into the bubble solution
*withdraw them nearly horizontally
*tip them gently to allow the water to drain off until soap film settles in one position

This shows dipping the plates into the bubble solution and removing them horizontally.
This shows the minimum length linking the four points.
Again, this shows the tendancy toward minimum surface area. You can see the nearly 120 degree angels.