  The process of drop formation from a nozzle can be seen in many natural
systems and engineering applications. Here, we investigate the formation of a
liquid droplet from a wettable nozzle. The behavior of a drop is complicated
due to an interplay among gravity, capillary rise, viscous drag, and surface
tension. In experiments, we observe that drops forming from a wettable nozzle
initially climb the outer walls of the nozzle due to surface tension. Then,
when the weightof the drops gradually increases, they finally fall due to
gravity. By changing the parameters like the nozzle size and fluid flow rate,
we have observed that different behaviors of the droplets. Such oscillatory
behavior is characterized by a nonlinear equation that consists of capillary
rise, viscous drag, and gravity. Two asymptotic solutions in the initial and
later stages of drop formation are obtained and show good agreement with
experimental observations.
