Surface Wakes on Ultrasoft Solids

We explore the dynamical response of the free surface of an ultrasoft solid driven by a localized moving pressure disturbance. Experiments reveal a steady V-shaped wake analogous to a surface Mach wedge. A simple geometric argument provides a qualitative explanation consistent with observations. A theoretical framework combining elastodynamic, capillary, and gravitational effects yields a generalized dispersion relation that smoothly interpolates between Kelvin's theory of liquid interface wakes and Rayleigh's theory of elastic surface waves. Our analysis explains the observed Mach-like behavior quantitatively while also emphasizing how elastodynamic effects can generate effective damping through radiative leakage. Together, our experiments and theory reveal the existence of a new regime that bridges fluid and solid surface-wave physics, offering new routes for probing the dynamics of soft interfaces.