Mechanism of surface wetting: principle of least action

In this paper, a lot of natural phenomena are presented to show the universality of the principle of least action. The essence of surface wetting is illustrated by the principle of least action. At the same time, the energy formulation and differential formulation are proved to be equivalent for surface wetting phenomenon. Some physical phenomena are explained by the principle of least action, such as super-hydrophobic state of the lotus leaf, jumping on water of the water strider, directional motion of the liquid drop and capillary adhesion. Some philosophical meanings are also discussed in this paper.