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DY: Fachverband Dynamik und Statistische Physik
DY 57: Poster - Diffusion
DY 57.16: Poster
Thursday, March 19, 2015, 16:00–18:00, Poster A
How fast is a magnetic snail creeping down a hill? — •Anita Freundorfer, Stefan Hartung, Ingo Rehberg, and Reinhard Richter — Experimentalphysik 5, Universität Bayreuth, D-95440 Bayreuth, Germany
We investigate a permanent magnet floating on a drop of ferrofluid, which is positioned at the upper most end of an inclined plane of perspex. Releasing a trigger the magnet travels down the ramp leaving a trace of ferrofluid behind. For different angles of inclination α of the plane we record the time dependent position xα(t) of the magnet and determine its velocity vα(t) = dxα(t)/dt. The latter depends on the thickness hα(t) of the ferrofluidic film which is measured by means of light absorption. For a specific time we plot the layer thickness hα(t) versus the capillary number Ca = η · v/σ where η denotes the viscosity and σ the surface tension. In the regime Ca < 0.01 we find h ∝ Ca2/3, whereas for Ca > 0.01 the scaling h ∝ a · Ca1/2 is confirmed. These scaling laws for the film thickness are in accordance with those found for a vertical plate pulled out of a liquid [1]. After the magnet arrives at the bottom of the plane the latter is switched to α = 0. The magnet creeps back on its trace, up to the end, like an inverse snail absorbing its own slime, which is also investigated quantitatively.
- [1] S. Weinstein, K. Ruschak, Annu. Rev. Fluid. Mech. vol.76, 066301 (2004).