A Crown Prince or Crown Princess is the heir or heiress apparent to the throne in a royal or imperial monarchy. The wife of a crown prince is also titled crown princess. In Europe, lineal succession conventions usually dictate that the eldest child (as in Sweden, Belgium, Norway and the Netherlands) or the eldest son of the current monarch (Spain, United Kingdom, Denmark) fills this role as Crown Prince or Crown Princess..
Hydrostatics is the branch of fluid mechanics that studies incompressible fluids at rest. It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, the study of fluids in motion.
The water cycle or hydrologic is a continuous cycle where water evaporates, travels into the air and becomes part of a cloud, falls down to earth as precipitation, and then evaporates again. This repeats again and again in a never-ending cycle.