surface tension

surface tension tendency of liquids to reduce their exposed surface to the smallest possible area. A drop of water, for example, tends to assume the shape of a sphere. The phenomenon is attributed to cohesion, the attractive forces acting between the molecules of the liquid (see adhesion and cohesion ). The molecules within the liquid are attracted equally from all sides, but those near the surface experience unequal attractions and thus are drawn toward the center of the liquid mass by this net force. The surface then appears to act like an extremely thin membrane, and the small volume of water that makes up a drop assumes the shape of a sphere, held constant when an equilibrium between the internal pressure and that due to surface tension is reached. Because of surface tension, various small insects are able to skate across the surface of a pond, objects of greater density than water can be made to float, and molten lead when dropped into a cool liquid forms suddenly into shot. See capillarity .

surface tension (γ) Fluid surfaces may take on the behaviour of a stretched elastic membrane as a result of the tendency of a liquid surface to contract. The surface tension of a liquid is given as the tension across a unit length of the fluid surface. Surface tension is temperature-dependent and is closely associated with capillarity.