What is the Difference Between Surface Tension and Capillary Action?

Surface tension and capillary action are both physical properties of liquids, but they differ in their definitions and applications.

Surface Tension:

Surface tension is a phenomenon in which the surface of a liquid, where it is in contact with a gas, acts like a thin elastic sheet.
It is measured as the force applied on a certain length of the liquid given by the unit against the gravity given by the unit m (meter).
Surface tension arises from the greater attraction of water molecules for each other, resulting in a high surface tension for water.

Capillary Action:

Capillary action occurs when the adhesion to the surface material is stronger than the cohesive forces between the water molecules.
It is measured as the height of the liquid column that is drawn upward, against the gravity given by the unit m (meter).
Capillary action is observed in plants, where it helps bring water up into the roots and distribute it throughout the plant.

The key difference between surface tension and capillary action is that surface tension is a measure of the force applied on a liquid's surface, while capillary action is the movement of a liquid along a surface due to adhesive forces. Both properties are related to the cohesive and adhesive forces of the liquid but manifest in different ways. For example, capillary action only occurs when the adhesive forces are stronger than the cohesive forces, which invariably becomes surface tension in the liquid.

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What is the Difference Between Surface Tension and Capillary Action?

Comparative Table: Surface Tension vs Capillary Action

Surface tension and capillary action are both properties of liquids that involve the forces of cohesion and adhesion. However, they differ in their definitions, measurements, and effects on liquids. Here is a table comparing the two:

Property	Definition	Measurement Unit	Effect on Liquids
Surface Tension	The force on the surface of a liquid exposed to air, causing the surface to behave like a stretched rubber membrane.	N/m (Newton per meter)	Flattens the curved liquid surface in a capillary tube, resulting in a downward force in mercury and an upward force in water.
Capillary Action	The tendency of a fluid to rise or fall in a narrow tube (capillary) depending on the combination of cohesive and adhesive forces.	Not measured in units, but rather as the height of the liquid column drawn upward against gravity (in meters)	Moves liquids horizontally over large distances, either raising or suppressing the liquid inside the tube depending on the relative strength of cohesive and adhesive forces and the contact angle.

Surface tension is the result of cohesive forces between molecules at the surface of a liquid, while capillary action is the result of both cohesive and adhesive forces between the liquid and the surface of a narrow tube. Capillary action can move liquids against external forces, such as gravity, when the adhesive forces between the liquid and the tube are stronger than the cohesive forces within the liquid.

Guilherme Mazui

Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.