The spiral vortex. A story about tornados and bathtubs

Abstract: In this paper, we show that equiangular spirals (also known as logarithmic spirals) appear naturally in fluids going through sinks. We provide a simple mathematical model that explains the spiral forms in some natural formations. For this model we need only small parts from the theories of complex variables and differential equations. The purpose of this educational paper is to stimulate students for further studies in fluid theory and differential equations.