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Sumit Kumar Birwa (ICTS-TIFR, Bangalore)
Date & Time
Fri, 03 August 2018, 11:15 to 12:15
Emmy Noether Seminar Room, ICTS Campus, Bangalore

In this talk, I will show how we studied experimentally the collision between a sphere falling through a viscous fluid, and a solid plate below. It is known that there is a well-defined threshold Stokes number above which the sphere rebounds from such a collision. Our experiment tests for direct contact between the colliding bodies, and contrary to prior theoretical predictions, shows that solid-on-solid contact occurs even for Stokes numbers just above the threshold for rebounding. The dissipation is fluid-dominated, though details of the contact mechanics depend on the surface and bulk properties of the solids. Our experiments and a model calculation indicate that mechanical contact between the two colliding objects is generic and will occur for any realistic surface roughness. After this, if the time permits, I will also explain the mathematical structure of the theory I am working on.