School of Physics Lecture Demonstration Manual

Fb-3Soap Bubble Paradox

Published: Thursday 09 March 2006 - Updated: Tuesday 29 March 2011


To show that small bubbles have greater air pressure inside them than larger bubbles.



Click on pictures to enlarge.

Soap Bubble Paradox Diagram


a) Principle of physics illustrated

In a soap bubble the excess pressure is related to the surface tension and radius by

A bubble is blown in each of the two pipes with the communicating tap closed. The bubbles are blown of nearly equal size. When taps B are opened the small bubble gets smaller and blows out the larger one, showing that the pressure was lareger in the smaller bubble.

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