Thecaseoftheoscillatingparty.PDF

The case of the oscillating party balloon: A simple toy experiment requiring a not-so-simple interpretation Amnon Yariv Department of Applied Physics, California Institute of Technology, Pasadena, California 91125 Jacob Scheuera School of Electrical Engineering, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, Israel 69978 Bruno Crosignani and Paolo Di Porto Dipartimento di Fisica, Universita’ dell’Aquila, L‘Aquila, Italy and Research Center Soft INFM-CNR c/o Universita’ di Roma, “La Sapienza,” Rome, Italy Received 29 November 2006; accepted 30 March 2007 The intriguing midair oscillations of a party balloon, which occur once its buoyancy is no longer capable of keeping it against the ceiling, is shown to require a rather sophisticated explanation in terms of variable-mass dynamics. The ubiquity of this phenomenon, the accessibility of its actual observation, and the subtlety of its analytic description provide a good opportunity for an interesting zero-cost classroom demonstration. © 2007 American Association of Physics Teachers. DOI: 10.1119/1.2733684 I. INTRODUCTION Even though lighter-than-air balloons have been around for a long time, this particular kind of problem seems to have Under usual circumstances, metallic party balloons do not been almost completely overlooked. The dynamics of a offer an occasion for any profound thought about their be- balloon-payload system was studied in Ref. 1, and the oscil- havior. They move, under the combined influence of gravity lations of a gas balloon due to temperature gradients were and Archimedes’ force, toward the c