Surface Tension

Surface tension refers to the stretchability of a liquid surface. To put it another way, surface tension refers to the difficulty of breaking through the surface of a liquid. Water has a high surface tension, second only to mercury.

Surface tension depends on the cohesion of water. When water comes into contact with air the water molecules have a greater attraction to water molecules than to molecules in the air. As a result, the water molecules are pulled downward as they bond with other water molecules and they are more closely crowded together than they would be beneath the surface. Therefore, the surface of the water appears to have a film or skin on top which can support the weight of an insect or a straight pin.

• Why doesn't a water ring usually flatten and spread out over a table top?
• If a water ring does spread out, why does that happen?
• Why can a slightly overfilled glass not spill over?
• Why do stones skip across the surface of a pond?
• Why can whirligig beetles live on the surface of water?
• What effect do dissolved solids have on the surface tension of water?

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