Résumé:

We demonstrate the instability of the free surface of a soft elastic layer facing downwards. Experiments are carried out using a system consisting in a gel of constant density and shear modulus , put in a rigid cylindrical dish of depth h. When turned upside down, the free surface of the gel undergoes a normal outgoing acceleration g., whereas a steady pattern spontaneously appears in the opposite case. This phenomenon results from the interplay between the gravitational energy and the elastic energy of deformation of the system