Capillarity

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Capillarity Meaning

Capillarity meaning is very simple to understand in terms of hydrodynamics. Capillarity is an invisible force that works against the force of gravity. It pushes a liquid up in a tube or a narrow pipe. This rising of liquid is the capillary action. We call such liquid capillary water because the water follows the principle of capillarity.

In this article, we will learn how to do the capillary definition, discuss the capillary action definition, explain capillary action, understand the capillary water meaning, define capillary action, and understand the capillary action in detail.


Define Capillary Action

Capillary action is the force or an effort made to push the liquid by fighting the gravitational force of attraction. Also, after a certain amount of time, the liquid falls. This fall occurs when the liquid faces a surface tension.


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For measuring the temperature of our body, we use a clinical thermometer. Generally, a digital thermometer takes 60 seconds to determine the temperature. So, there is another thermometer, which is a mercury thermometer, which displays the temperature in the form of mercury rise. The division at which the mercury rise stops is the ultimate body temperature.

So, here, the mercury rise is the capillary action. Here, we also notice that after some time, the mercury falls. So, the rise and fall of the mercury is also the capillary action.

In this text, we included the topic ‘surface tension,’ do you know what surface tension is? So, let’s understand this terminology:


Surface Tension

In Physics, the tension on the surface of the film of a liquid occurs because of the attraction of the surface particles by the bulk of the liquid that tries to minimize the surface area of the liquid drop, and this phenomenon is called surface tension. When the surface of the liquid is very strong, the surface tension is applicable and the liquid can hold weight.

In simple words, the definition of surface tension in capillary action definition is as follows:

Surface tension is the ability of liquid surfaces to shrink into the minimum possible surface area. Surface tension allows insects like water striders to swim and slide on a water surface without becoming even partly dipped. 


Do You Know?

We see that at the liquid–air interfaces, surface tension always results from the greater attraction or cohesion of liquid molecules to each other than to the molecules in the air or adhesion. 


Capillary Define

Now, we will understand the capillarity water meaning and explain capillary action with the help of real-life applications:

  1. When we pour the kerosene oil in a lantern and the melted wax in a candle, the capillary action forms in the cotton wick and burns.

  2. The coffee powder gets dissolved in water easily because water immediately wets the fine granules of coffee by the action of capillarity.

  3. The water poured into the grassland rises in the uncountable capillaries formed in the stems (Xylem) of plants and trees and reaches the leaves. 

  4. The tip or the nib of a pen splits to provide capillary action for the ink to rise, which helps us to write on the paper.

  5. After taking a bath, we use a towel, the action of a towel in soaking up moisture from the body is due to the capillary action; also known as capillary water.

Capillary Action Formula Derivation

The ascent of a liquid column in a capillary tube is given by the following equation:

h = 2Scosθ/rρg − r/3

Now, let’s do the capillary action formula derivation:

If the capillary is very narrow, then we have:

h = 2Scosθ/rρg

Where,

h =  height of the capillary tube

r is the radius of the capillary tube,

ρ is the density of the liquid or water,

θ = angle of contact

Here, the angle of contact is the angle between the tangent drawn to the liquid surface at a certain point of contact of liquid and solid inside the liquid.

The angle of contact relies on the nature of both solid and liquid. For the concave meniscus of liquid, the angle of contact will be acute, while for the convex meniscus of liquid, it will be obtuse.

S = surface tension of the liquid/fluid/water


Point To Note:

At equilibrium, the height (h) does not depend on the shape of the capillary when the radius of the meniscus remains unchanged. Due to this reason,  the vertical height (h) of a liquid column in capillaries of different sizes and shapes also remains the same.

Now, let’s consider a few cases to see if the liquid rises, falls, or remains unchanged:

  • If θ < 90°, which means cos θ is positive, so ‘h’ is also positive, i.e. liquid rises in a capillary tube.

  • If θ > 90°, which means cos θ is negative, so ‘h’ is negative, i.e. liquid falls in a capillary tube.

  • The rise of liquid in a capillary tube agrees and totally follows the law of conservation of energy.

FAQ (Frequently Asked Questions)

1. Define Adhesion and Cohesion.

Ans: The force that persists between the molecules of certain liquids is the cohesive force.  For example, raindrops, before they fall, come together by the same force. 

Surface tension is a phenomenon that comes under the concept of cohesion. Surface tension allows materials that are denser than the liquids to swim on top of them without any support and doesn’t let them submerge.

Adhesion is the force of attraction between two uncommon substances such as liquid and a solid vessel. The adhesive force allows water to stick to the glass. 

Liquids like mercury have more cohesive force than adhesive and thus can be termed as non-wetting liquids. Such liquids curve inwards when they are near the edge of the container.

2. State the Cause of Capillary Action.

Ans: Capillary action is the spontaneous flow of a liquid into a narrow tube. This movement does not need a gravitational force to occur. It acts in an opposite direction to the force of gravity. Capillary action is referred to as capillary motion, capillarity, or wicking.

Capillary action is caused by the total effect of liquid cohesive forces and the adhesive forces between the liquid and the porous material (Where cohesion and adhesion are two types of intermolecular forces). These forces raise the liquid into the tube. For capillarity to occur, a tube needs to be small in diameter.

The example of capillarity involves the uptake of water in paper and plaster a.k.a two porous materials, the absorption of paint between the hairs of a paintbrush, and the water movement via sand.