Surface tension in a liquid arises because
Correct answer: A. molecules at the surface are pulled inwards and sideways only, with no upward pull
- A. molecules at the surface are pulled inwards and sideways only, with no upward pull
- B. the surface molecules move faster than those inside
- C. air presses down on the surface
- D. the liquid evaporates from the surface
Explanation
A molecule inside the liquid is pulled equally in all directions, but one at the surface has no neighbours above it, so the net inward pull makes the surface behave like a stretched skin and contract to the smallest possible area. This is why free drops are spherical and why a needle can float on water. Surface tension falls as temperature rises, because the molecules are harder to hold together.
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About Properties of Liquids
Liquid behavior depends on intermolecular forces, which produce surface tension, viscosity, capillary action and a definite volume without a fixed shape. The topic also covers vapor pressure, evaporation, boiling point and the effect of temperature and external pressure, while distinguishing evaporation at the surface from boiling throughout the liquid.
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