Meniscus (liquid)

A meniscus is the curve in the surface of a liquid at the point where it touches its container, caused by surface tension and adhesion. The shape of the meniscus can be either concave (curving upwards) or convex (curving downwards), depending on the relative strength of the cohesive forces within the liquid and the adhesive forces between the liquid and the container material.

A concave meniscus occurs when the liquid's molecules are more strongly attracted to the container (adhesion) than to each other (cohesion). Water in a glass tube is a common example, where the water molecules are attracted to the silica in the glass, causing the water to climb the sides of the tube and form an upward-curving meniscus.

A convex meniscus occurs when the liquid's molecules are more strongly attracted to each other (cohesion) than to the container (adhesion). Mercury in a glass tube is a common example. The mercury atoms have a strong attraction to each other, causing them to minimize their contact with the glass and form a downward-curving meniscus.

When measuring the volume of a liquid in a graduated cylinder or other measuring device, the reading should be taken at the bottom of the concave meniscus or the top of the convex meniscus to ensure accurate measurement. Ignoring the meniscus can lead to systematic errors in volumetric measurements.