Surface tension is the tendency for the surface of a liquid to act like a stretched membrane or piece of rubber. The cohesive forces work to bring the molecules on the interior of the liquid to the exterior surface. If you want to get scientific, surface tension is numerically equal to the force acting at right angles to a line of unit length that is lying on the surface and is called Constant of Capillarity and is represented by the symbol T. Capillarity is the interaction between contacting surfaces of a liquid and a solid that distorts the liquid surface from a planar, flat or two-dimensional, shape to concave or convex.
Cohesion is the attraction of molecules by which the elements of the body are held together. Water has the highest cohesive force of any liquid except that of mercury. At the air-water interface, the water molecules are H-bonded to one another and to the molecules below the surface. This makes the water behave as though it were coated with an invisible film.
Walking on Water
The main reason why certain creatures can “walk” on water and we can’t is because their bodies have tiny, little hairs on the bottom of their legs and feet. Their body weight is so minute that it only creates a dimple in the water’s surface which allows the insect to literally “walk on water.” Our body weight is too much for the cohesive forces of the water and we break through the invisible film that the tension creates.
Have you ever heard of the smiling spiders? Theridion Grallator, also known as the happy face spider, is known for having a pattern of a smiley face or a clown grin on its back. These happy creatures live in rainforests and each spider has a unique pattern. It seems like spiders are not that scary after all.