Physics of soap films – inquiry problems for 12th grade of the Bulgarian school

For centuries, soap bubbles have captured people's imagination. Bubbles have been a source of entertainment, inspiration for paintings, an incentive for philosophers and poets to compare their short lives to human life, and, of course, a huge challenge for scientists. Newton studied iridescent colors, Joseph Plateau proved the existence of a minimal two-dimensional surface with a given closed boundary, and Lord Kelvin in 1887 searched for the arrangement of cells or bubbles with a minimal total surface area between them. According to him, one can dedicate whole life to discovering physical laws just by blowing a soap bubble. Studying soap bubbles at school is beneficial from both theoretical and practical perspectives. The report discusses the application of an inquiry approach to studying the topics of liquid properties and surface tension. The topic is studied in grade twelve of the profiled physics curriculum in Bulgarian School. Teaching takes place at several levels. Students are introduced to basic concepts, principles, and laws of fluids. A structured study is then conducted in which the surface tension coefficient is determined by several different methods. The properties of soap films are studied through guided investigation, in which students are presented with research questions, and they develop research procedures. The geometric and optical properties of two-dimensional membranes and the interaction between soap bubbles are studied. From the two-dimensional membrane between soap bubbles, we move on to three-dimensional bubbles and the study of their properties. Advantages of the approach under consideration are the creation of interest and engagement of students, deepening of their mathematical knowledge, and the opportunity for interdisciplinary lessons in chemistry and art.