Surface Tension Facts

Surface tension is a physical property of liquids that comes from imbalanced cohesive forces at or near the surface of that liquid, which in turn causes the liquid to contract for a minimal exposed surface area. Experts state that the exposed surface retains a stretched elastic-type membrane that makes it more difficult to move an object through the surface than completely submersed in the liquid.

Observable instances of surface tension

There are a number of examples in nature that can be easily observed which help demonstrate the property of surface tension. When rain or dew beads up into drops on a waxy leaf, surface tension holds it in a defined shape. The cohesive force between the molecules of water is stronger than the adhesive force between the waxy leaf and the water so the water molecules contract into a drop shape, minimizing its exposed surface area. When an object is non-porous and is heavier than the water itself, but is light enough to be supported by the forces arising from the surface tension of the water, the object will float. Such is the case in an insect such as a water strider walking across the surface of a pond. The pressure from the water strider's feet causes indentations in that "film," which serves to further increase the surface tension of the water. Separation of dissimilar liquids is yet another example. Oil and water will not mix because of the tension formed between the two different liquids, causing a phenomenon called interface tension.

Importance of surface tension

While surface tension may seem like an esoteric property that is valuable only to scientists, its manipulation has many real-world everyday applications. Many camping tents are constructed of materials that are woven in such a way that the pores of the material are "bridged" by the surface tension of rain. If you touch the material, the surface tension of the water is broken and the rain slips through the tent material.

The surface tension of water decreases as water gets hotter. The less the surface tension is, the greater its ability to soak through cloth. This is why we tend to do laundry with hot or warm water. Detergents act to decrease surface tension as well; that's why you're able to use cold water when doing laundry with detergent.

Disinfectants usually contain chemicals called surfactants, which also act to decrease surface tension. This helps them to spread out over the surface of the bacteria, and disrupt their cell walls.

In the medical laboratory, the property of surface tension can be used to confirm jaundice. The Hay test involves sprinkling powdered sulfur on the surface of the urine. If the person does not have jaundice, the powder will float. But if the person does have jaundice that means that there is bile in their urine. The bile lowers the surface tension of the urine, and the powdered sulfur will sink below the surface of the urine.

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