Surface Tension

My problem was to find out how to test or measure surface tension. I think the reason of some of the force in surface tension is cohesion and gravity. Surface Tension is the condition existing at the free surface of a liquid, resembling the properties of an elastic skin under tension. The tension is the result of intermolecular forces exerting an unbalanced inward pull on the individual surface molecules; this is reflected in the considerable curvature at those edges where the liquid is in contact with the wall of a vessel. Because of this property, certain insects can stand on the surface of water. A razor blade can also be supported by the surface tension of water. The razor blade is not floating: if pushed through the surface, it sinks through the water. More specifically, the tension is the force per unit length of any straight line on the liquid surface that the surface layers on the opposite sides of the line exert upon each other. The tendency of any liquid surface is to become as small as possible as a result of this tension, as in the case of mercury, which forms an almost round ball when a small quantity is placed on a horizontal surface. The near-perfect spherical shape of a soap bubble, which is the result of the distribution of tension on the thin film of soap, is another example of this force; surface tension alone can support a needle placed horizontally on a water surface. Surface tension depends mainly upon the forces attraction between the particles within the given liquid and also upon the gas, solid, or liquid in contact with it. The molecules in a drop of water, for example, attract each other weakly. Water molecules well inside the drop may be thought of as being attracted equally in all directions by the surrounding molecules. However if surface molecules could be displaced slightly outward from the surface, they would be attracted back by the near by molecules. The energy responsible for the phenomenon of surface tension may be thought of as approximately equilivant to the work or energy required to remove the surface layer of molecules in a unit area. In comparison, organic liquids, such as benzene and alcohol's, have lower surface tensions, whereas mercury has a higher surface tension . An increase in temperature lowers the net force of attraction among molecules and hence decreases surface tension. Surface tension is also viewed as the result of forces acting in the plane of the surface and tending to minimize its area. On this basis. surface tension is often expressed as amount of force exerted in the surface perpendicular to a line of unit length. The unit then is Newton's per metre, which is equivalent to joules per square metre. Surface tension is important at zero gravity, as in space flight: Liquids cannot be stored in open containers because they run up the vessel walls. Cohesion is phenomenon of intermolecular forces holding particles of a substance together. Cohesion in liquids is reflected in the surface tension caused by the unbalanced inward pull on the surface molecules, and also in the transformation of a liquid into a solid state when the molecules are brought sufficiently close together. Cohesion in solids depends on the pattern of distribution of atoms, molecules, and ions, which in turn depends on the state of equilibrium (or lack of it) of the atomic particles. In many organic compounds, which form molecular crystals, for example, the atoms are bound strongly into molecules, but the molecules are bound weakly to each other. Bibliography: Microsoft Encarta 95 1994 Funk & Wagnall's Corporation Encyclopedia Britannica 1988 vol.11 15th Edition Encyclopædia Britannica, Inc. Compton's Encyclopedia 1988 vol.22 Edition Encyclopædia Britannica, Inc.