At any given instance, the inertial force of the entire
drop is balanced by the pressure (hydrostatic) and viscous
forces as shown in equation (8), which is the volume integral
form of equation (2) (ignoring the gravitational term
for horizontal vibration):Numerical simulation shows that all the three terms of
equation (8), i.e. the inertial force (the term on the left),
the hydrostatic force (first term on right), and the viscous
force (second term on the right), change at resonance, with
the hydrostatic force varying with a different phase than
the other two forces. While any of the above forces can
be used to identify the resonance modes of a drop, we use
the hydrostatic force to achieve this goal. Numerical sim-