A simple mechanical apparatus for measuring the surface tension of soap bubbles

We report on the construction of a simple apparatus for measuring the small overpressure inside soap bubbles with sizes in the cm range. The apparatus uses Archimedes' principle and it can be easily calibrated. Thus, surface tensions of soap films can be measured quantitatively. The apparatus is also well suited to demonstrate the Young–Laplace law in front of an audience such as a classroom. The design of the apparatus is subject to a criterion for stability, which we discuss in detail and that can be discussed with the audience. The setup of the apparatus requires components that are commonly available in households or school labs and it can be set up by students on their own.We report on the construction of a simple apparatus for measuring the small overpressure inside soap bubbles with sizes in the cm range. The apparatus uses Archimedes' principle and it can be easily calibrated. Thus, surface tensions of soap films can be measured quantitatively. The apparatus is also well suited to demonstrate the Young–Laplace law in front of an audience such as a classroom. The design of the apparatus is subject to a criterion for stability, which we discuss in detail and that can be discussed with the audience. The setup of the apparatus requires components that are commonly available in households or school labs and it can be set up by students on their own.