  We consider a fluid-structure interaction system composed by a rigid ball
immersed into a viscous incompressible fluid. The motion of the structure
satisfies the Newton laws and the fluid equations are the standard
Navier-Stokes system. At the boundary of the fluid domain, we use the Tresca
boundary conditions, that permit the fluid to slip tangentially on the boundary
under some conditions on the stress tensor. More precisely, there is a
threshold determining if the fluid can slip or not and there is a friction
force acting on the part where the fluid can slip. Our main result is the
existence of contact in finite time between the ball and the exterior boundary
of the fluid for this system in the bidimensional case and in presence of
gravity.
