We present the results of a combined experimental and theoretical investigation
of droplets falling onto a horizontal soap film. Both static and vertically vibrated
soap films are considered. In the static case, a variety of behaviours were observed,
including bouncing, crossing and partial coalescence. A quasi-static description of
the soap film shape yields a force–displacement relation that provides excellent
agreement with experiment, and allows us to model the film as a nonlinear spring.
This approach yields an accurate criterion for the transition between droplet bouncing
and crossing. Moreover, it allows us to rationalize the observed constancy of the
contact time and scaling for the coefficient of restitution in the bouncing states.
On the vibrating film, a variety of bouncing behaviours were observed, including
simple and complex periodic states, multi-periodicity and chaos. A simple theoretical
model is developed that captures the essential physics of the bouncing process,
reproducing all observed bouncing states. The model enables us to rationalize
the observed coexistence of multiple periodic bouncing states by considering the
dependence of the energy transferred to the droplet on the phase of impact.
Quantitative agreement between model and experiment is deduced for simple
periodic modes, and qualitative agreement for more complex periodic and chaotic
bouncing states. Analytical solutions are deduced in the limit of weak forcing and
dissipation, yielding insight into the contact time and periodicity of the bouncing
states.