Capillary Action

What is Capillary Action?

Capillary action refers to the movement of a liquid through a narrow tube against the force of gravity. This phenomenon is commonly observed in thin tubes or porous materials, such as plant stems or soil.

Mechanism of Capillary Action

Capillary action is driven by the interaction between cohesive forces within the liquid and adhesive forces between the liquid and the capillary walls. Cohesive forces tend to draw liquid molecules together, while adhesive forces attract liquid molecules to the surface of the capillary.

In a narrow tube, the adhesive forces become stronger than the gravitational forces acting downwards on the liquid. This imbalance causes the liquid to rise within the tube, creating a curved surface known as a meniscus.

Factors Influencing Capillary Action

• Tube diameter: Capillary action is inversely proportional to the diameter of the tube. The narrower the tube, the higher the capillary rise.
• Liquid properties: Liquids with higher surface tension and density exhibit greater capillary action.
• Capillary material: The nature of the capillary material also influences capillary action. Materials with hydrophilic surfaces (e.g., glass) promote capillary action, while hydrophobic surfaces (e.g., Teflon) resist it.

Applications of Capillary Action

Capillary action has numerous applications, including:

• Water uptake by plants: Capillary action allows plants to absorb water from the soil through their roots.
• Ink flow in pens: Capillary action draws ink from the reservoir to the tip of a pen, enabling writing.
• Chromatography: Capillary action is used in paper chromatography to separate and identify chemical substances.

Acceptable Damp Reading

In the context of building materials, an acceptable damp reading is influenced by various factors, including the type of material and its intended use. Generally, a moisture content below 15% is considered acceptable in most situations.