Capillary action

Definition

Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces. It occurs due to the adhesive force between the liquid and the surface and the cohesive forces within the liquid.

5 Must Know Facts For Your Next Test

1. Capillary action is driven by adhesive forces between the liquid and a solid surface, and cohesive forces within the liquid.
2. The height to which a liquid can rise or fall in a capillary tube is inversely proportional to the diameter of the tube.
3. Water exhibits strong capillary action because of its high adhesion to surfaces like glass and its strong cohesion due to hydrogen bonding.
4. Capillary action is essential for processes like water transport in plants, where it helps move water from roots to leaves through xylem vessels.
5. The contact angle between the liquid and solid surface affects capillary action; smaller contact angles result in stronger capillary rise.

Review Questions

• What forces drive capillary action?
• How does the diameter of a capillary tube affect the height of liquid rise?
• Why is capillary action important for plant water transport?

Related terms

Cohesion:

The intermolecular attraction between like molecules, such as hydrogen bonds between water molecules.

Adhesion:

The intermolecular attraction between unlike molecules, such as water molecules adhering to glass.

Surface Tension:

\text{A physical property caused by cohesive forces at the surface of a liquid, causing it to behave as if covered by an elastic sheet.}