Viscosity is a measure of the resistance of a fluid to deform under either shear stress or extensional stress. It is commonly perceived as "thickness," or resistance to flow. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin," having a lower viscosity, while vegetable oil is "thick" having a higher viscosity. All real fluids (except superfluids) have some resistance to stress, but a fluid that has no resistance to shear stress is known as an ideal fluid or inviscid fluid. The study of viscosity is known as rheology.
From a Unification perspective, several points can be made:
- The scientific study of viscosity and the use of this knowledge are manifestations of our higher intelligence, rational thought, and creativity. These attributes are linked to our spiritual dimension and set us apart from other known species on Earth. Moreover, these attributes are reflective of God's intelligence, rational thought, and creativity.
- Our study of viscosity corresponds to internal, mental activities; our uses of this knowledge for practical applications involve external, physical actions. Thus the internal and external aspects of each person's make-up work together. Unification Thought points out the need for harmonious interactions between these complementary aspects, in order for us to accomplish higher goals and feel joy in our lives.
- We have an inner drive to understand viscosity and use this knowledge to make things for our benefit. By fulfilling this inner drive, we move toward fulfilling what Unification Thought calls God's Third Great Blessing to humanity—namely, to understand the natural world, harmonize with it, and establish a dominion (stewardship) of love over it.
- Our knowledge of viscosity and practical use of this knowledge are ways to serve the common human good. By taking responsibility and exerting our efforts to serve others, we become channels for God's love to flow through us to others and to the rest of creation. In this manner, we can fulfill what Unification Thought calls God's Three Great Blessings and establish a world of peace and harmony.