Surface Tension and Capillary Phenomena
Why the surface of a liquid behaves like a stretched elastic skin
Big idea: The molecules at the free surface of a liquid pull on each other so that the surface tries to shrink to the smallest possible area. This gives the surface a stretched-skin behaviour called surface tension. The same molecular forces let a liquid climb up thin tubes on its own — a capillary phenomenon.
By the end of this lesson you will be able to:
- explain surface tension from the forces between molecules;
- use the surface-tension coefficient σ and the formula F = σL;
- tell wetting liquids from non-wetting liquids by the shape of the meniscus;
- use the capillary-rise formula h = 2σ/(ρgr);
- give real examples of surface tension and capillarity in nature and everyday life.