  This paper proposes a new general methodology for finite-time singularity
formation for moving interface problems involving the incompressible Euler
equations in the plane.
  The first problem considered is the two-phase Euler vortex sheets problem
with surface tension for which is proved the finite time singularity of the
natural norm of the problem for suitable initial data. This is in striking
contrast with the case of finite time splash and splat singularity formation
for the one phase Euler equations introduced in [4] and studied in a more
general context in [8], for which the natural norm (in the one phase fluid)
stays finite all the way until contact.
  The second problem considered involves the presence of a heavier rigid body
moving in the perfect fluid. We first establish that the rigid body will hit
the bottom of the fluid domain in finite time (in a more general context and
very different methodology than first done for this problem in [19]). We next
establish that a surface energy blows up, and characterize the acceleration of
the rigid body at contact, depending on the nature of the contact zone:
Acceleration opposes the motion at contact, and is either positive finite if
the contact zone contains a curve, or infinite otherwise.
