ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY. ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY.
Concave meniscus of a glass of water supporting a paper clip. The meniscus, the curved surface of water, is concave due to its surface tension properties: the ability of the liquid surface to act like a stretched membrane and support the paperclip is also due to surface tension. Surface tension effects arise because of the interractions between molecules in the water at the boudary with another medium (ie air). In a more viscous liquid the meniscus would be convex.
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