Study on the magnetic levitation of a magnetic flea

We investigated the problem of 'magnetic levitation' originating from the 33rd International Young Physicists' Tournament (IYPT). The problem was first investigated by a PRL paper (Baldwin et al.) in 2018, which states that the flea of a magnetic stirrer spinning fast enough in a liquid with a high viscosity coefficient can jump from the bottom and levitate stably. The magnetic force and gravity balance periodically. This phenomenon includes several concepts: magnetic dipoles, rigid-body rotation, fluid mechanics and magnetic levitation. They are more or less unfamiliar to undergraduate students. However, the movement of the flea could be described with a concise forced vibration equation, which is familiar in textbooks. The phenomenon could be divided into two stages: synchronous movement and levitation state. The transition is the jumping of the flea. We demonstrated this process and presented several equations to build this physical model. The progression of the phenomenon is due to the increase in the drive magnet angular velocity called the drive velocity. We verified our theory by simulation and experiments. Several parameters are experimentally verified to influence the phenomenon. We also discussed the origin of dynamic stabilization, which would be slightly complicated but worthy for students. In short, we introduce an interesting problem originating from the PRL paper that can be easily achieved under laboratory conditions. We extend some content in a pedagogical way that would be helpful for students to understand the related physical concepts, such as the influence of the viscosity coefficient of the liquid on the flea's motion, which is not discussed in the PRL paper.