Bubbles and Capillary Rise

Capillarity is the depression or rise of a liquid in a narrow passage. For example, water seeping in the gaps between the fibres of a towel or the holes in a porous material. Other names for this behaviour include capillary motion, capillarity or wicking. 

Capillary action is not restricted to the vertical plane. It mainly occurs due to cohesive and adhesive forces.  

This article will discuss the phenomenon of capillary rise, along with the capillary rise formula and other concepts. So, without further ado, let us get started with the bubbles and capillary rise.

Introduction to Cohesive and Adhesive Forces 

The cohesive forces are attractive forces present between molecules of similar types. On the other hand, the adhesive forces are those forces that are attractive within different kinds of molecules. 

One typical example is the attraction between the water molecules in a glass and the glass molecules. 

When any liquid comes into contact with any surface, such as the table top or walls of the graduated cylinder, it is subjected to both adhesive and cohesive forces. Note these forces play a significant role in determining the shape of the liquid. 

Explaining Capillary Rise

Sometimes referred to as capillary motion or capillarity, we can describe the capillary as the liquid’s ability to flow from extremely narrow spaces. 

As mentioned earlier, capillary action is not restricted to the vertical plane. For instance, assume water coming in contact with a towel. The water gets sucked into the fibres without depending on the orientation of the towel or cloth.

In simple terms, we can define capillary rise as a phenomenon in which liquid ascends through the tube or cylinder. It is another common phenomenon that takes place due to the surface tensions of liquid. 

If the water is stored in a narrow measuring cylinder or the beaker, you will notice that the meniscus surface is not straight, it develops a slight depression. This behaviour occurs due to adhesive forces between the surface and the water. 

Now imagine you place a thin tube inside the water tub. Will the water level rise? 

If the adhesive force is greater than that of the cohesive forces in the water molecule, the water is most likely to rise. 

Equation of Capillary Rise

Here is the question at which the water is most likely to rise – 

h = 2σ / ρrg

Here,

h denotes the height of raising liquid by capillary action

σ denotes surface tension

r denotes the radius of the tube

ρ indicates the density of the liquid

g represents acceleration due to gravity.

The liquid in the beaker rises due to adhesion, cohesion and surface tension forces. In the case of the adhesive, the liquid-capillary forces are higher than that of the cohesive liquid-liquid forces; the liquid rises in the same way as the water rises in a glass capillary. Here, the contact angle is lower than 90 degrees. 

If the adhesive force is lower than the cohesive force, then the liquid in the beaker decreases in the same way as in the case of mercury. Forces that balance the liquid column are useful to drive the formula for rising in the capillary. 

The force that is upward owing to surface tension is 2πrσcosθ, which balances the weight of the liquid πr2hρg. This capillary rise formula can also be attained using the balance pressure. 

The Pressure Inside a Bubble 

Plant absorbing water from the soil to complete the process of photosynthesis is a common phenomenon that you must have studied in lower classes. Have you ever imagined how all of this is possible?

Can you imagine water rising against gravity? 

Well, that’s not possible. 

However, it is yet another phenomenon that occurs. As mentioned earlier, if you take water in a beaker or a cylindrical tube, you can record that the water surface isn’t straight or the meniscus, as it develops a slight depression. It occurs due to adhesive forces. 

Conclusion 

With this, we end our study material on bubbles and capillary rise. We covered the introduction to bubbles and capillary rise, adhesive and cohesive forces in bubbles and capillary rise, the pressure inside a bubble and other related topics.

In this introduction to bubbles and capillary rise, we studied adhesive and cohesive forces in detail. The cohesive forces are adhesive forces present between molecules of a similar type. In contrast, the adhesive forces are those forces that are attractive within different types of molecules.

We hope the bubbles and capillary rise study material must have helped attain a greater understanding of this topic.