  Sessile drops of soft hydrogels were vibrated vertically by subjecting them
to a mechanically induced Gaussian white noise. Power spectra of the surface
fluctuation of the gel allowed identification of its resonant frequency that
decreases with their mass, but increases with its shear modulus. The principal
resonant frequencies of the spheroidal modes of the gel of shear moduli ranging
from 55 Pa to 290 Pa were closest to the lowest Rayleigh mode of vibration of a
drop of pure water. These observations coupled with the fact that the resonance
frequency varies inversely as the square root of the mass in all cases suggest
that they primarily correspond to the capillary (or a pseudo-capillary) mode of
drop vibration. The contact angles of the gel drops also increase with the
modulus of the gel. When the resonance frequencies are corrected for the
wetting angles, and plotted against the fundamental frequency scale
(gamma/mu)^0.5, all the data collapse nicely on a single plot provided that the
latter is shifted by a shear modulus dependent factor (1+mu.L/gamma). A length
scale L, independent of both the modulus and the mass of the drop emerges from
such a fit.
