Revisiting a Classic Magic Trick with Rayleigh–Taylor Instabilities

• Autores: Hollis Williams
• Localización: The Physics Teacher, ISSN 0031-921X, Vol. 61, Nº. 7, 2023, págs. 621-624
• Idioma: inglés
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• Resumen

  • A classic magic trick involves filling a bucket with liquid and then turning it upside down so that the liquid stays in the bucket. This does not work under normal circumstances because of the Rayleigh–Taylor instability. Although the atmospheric pressure pushing at the free surface from below is theoretically enough to support the surface, in reality any very small perturbation or disturbance of the surface causes it to ripple and form irregularities, which grow so that there is no longer a balance between the weight of the water and the pressure. In this article, I will help students understand the physics behind these instabilities by introducing a variation on a common type of geometry known as a Hele-Shaw cell and studying the influence of various factors that are involved in the physics of the magic trick, including the viscosity and surface tension of the liquid.