capillary rise

Capillary rise is the ability of a liquid to flow in narrow spaces without external forces, mainly due to the combination of cohesion (the attraction between similar molecules) and adhesion (the attraction between different molecules). For example, when a thin straw is placed in water, the water climbs up the straw because it sticks to the straw's walls (adhesion) while also pulling other water molecules along with it (cohesion). This effect is most noticeable in small tubes or porous materials and is important in nature, such as how plants draw water from the soil.