Meniscus (liquid)

In physics (particularly fluid statics), the meniscus (pl.: menisci, from Greek 'crescent') is the curve in the upper surface of a liquid close to the surface of the container or another object, produced by surface tension.

A concave meniscus occurs when the attraction between the particles of the liquid and the container (adhesion) is more than half the attraction of the particles of the liquid to each other (cohesion), causing the liquid to climb the walls of the container (see Surface tension § Causes). This occurs between water and glass. Water-based fluids like sap, honey, and milk also have a concave meniscus in glass or other wettable containers.

Conversely, a convex meniscus occurs when the adhesion energy is less than half the cohesion energy. Convex menisci occur, for example, between mercury and glass in barometers^[1] and thermometers.

In general, the shape of the surface of a liquid can be complex. For a sufficiently narrow tube with circular cross-section, the shape of the meniscus will approximate a section of a spherical surface, while for a large container, most of the upper surface of the liquid will be almost flat, only curving up (if concave) or down (if convex) near the edges.