Background Paper for Hydrostatics

Background
Physics is the study of non-living things. Physical science is one of the fundamental sciences because the other natural sciences like biology and geology deal with systems that obey the laws of physics. Engineering physics is the study of the combined disciplines of physics, engineering and mathematics in order to develop an understanding of the interrelationships of these three disciplines. “A study of hydrostatics can also include capillarity, the ideal gas laws, the velocity of sound, and hygrometry.” Hydrostatics is about the pressures given off by a fluid at rest. Fundamental physics is combined with problem solving and engineering skills. “The definition of a fluid deserves careful consideration. Although time is not a factor in hydrostatics, it enters in the approach to hydrostatic equilibrium.” It is usually stated that a fluid is a substance that cannot resist confining surfaces. Geology shows us clearly that there are substances which can resist forces but flow like a liquid over a long period of time, like wax, ice, and sometimes rock. There are lots of different topics in hydrostatics which often appear in introductory science. Water is incompressible, while air is very compressible, but both are fluids. Water has a definite volume; air does not. Water and air both have a low viscosity. Other fluids, like syrup, will have high viscosity, but they are no less fluids. “Hydrostatics deals with permanent, time-independent states of fluids, so viscosity does not appear. A fluid, therefore, is a substance that cannot exert any permanent forces tangential to a boundary.” The density of water is about 1 g/cm3, or its specific weight is 62.4 pcf. Surface tension is the tendency of the surface of a liquid that allows it to resist an external force. An example is, the floating of some objects on the surface of water, even though they are denser than water and also in the ability of some insects to run on the water surface. Surface tension has the dimension of force per unit length, or also of energy per unit area. These two are equal, but when talking about energy per unit of area, people use a different term which is a more general term in the sense that it applies also to solids and not just liquids. “The liquid molecules are responsible for the reaction of surface tension. In a liquid, each molecule is equally balanced in every direction by neighboring liquid molecules, resulting in a net force of zero.” The molecules at the surface do not have the other molecules on all sides of them and therefore are pulled inwards. This creates something called internal pressure which forces liquid surfaces to contract to the minimal area, like a penny. “Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer.” Usually when gravity is not applied water droplets are completely spherical. “The spherical shape minimizes the necessary "wall tension" of the surface layer.”
Another way to view surface tension is in terms of energy. “The interior molecules have as many neighbors as they can possibly have, but the boundary molecules are missing neighbors and therefore have a higher energy.” In order for the liquid to minimize its energy state, the number of boundary molecules has to decrease. When you decrease the number of boundary molecules, it results in a smaller surface area. As a result of the

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