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Balancing a ball on a moving vertical wall covered in viscous fluid


Tom Mullin

Manchester Centre for Nonlinear Dynamics,
Department of Physics and Astronomy,
Manchester University
Manchester, M13 9PL.


We present the results of experimental investigations into balancing heavy balls and cylinders on a vertical moving wall using a thin layer of very viscous fluid. It is found that balance can be achieved over a narrow range of wall speeds so that a particle can be held at a fixed height. The fluid motion around the object is complicated in detail and yet the critical values for fixed point behavior show simple scaling with the diameter of the particles. Fluctuations become important near critical conditions and clear dierences are found in the distributions for the motion of cylinders and spheres.