Physics_A Short Note On Cohesion And Adhesion Of Water

The ability of molecules of the same substance to stick together because of mutual attraction is known as cohesion. On the other hand, adhesion is the property of molecules of a different substance to stick together. For example, solids have higher cohesive properties, so two different solids don’t stick together upon contact. On the other hand, Gases have higher adhesive properties as two gases easily mix even if they are not in direct contact. A unique substance that has both properties of cohesion and adhesive is water. One can see water sticking together to form a ball daily. The sticking of water molecules together to form a ball is a cohesive property. However, it also has adhesive properties where one can find water to be touching the surface of the tube at a higher level.

In this blog, we will discuss water’s cohesive and adhesive properties. In addition to that, we will also discuss what surface tension is and the difference between cohesive and adhesive properties of water, meniscus and capillary action.

What is the cohesion of water?

Cohesion is a property that can be seen in similar molecules. In simple words, cohesiveness is the ability of molecules to stick together when they are brought near each other. Water is an element that is known to have one of the most robust cohesive properties. It forms hydrogen bonds when two or more water molecules are brought closer.  

What is the adhesion of water?

Adhesion is the property of molecules of different substances to stick with each other when brought in contact. For example, water can form molecular bonds with molecules of other substances. Capillary action and meniscus are two effects that explain adhesion property in water.

Effects of cohesion or adhesion of water

The surface tension of water

Surface tension is the cohesive forces between adjacent molecules of a substance. The molecules of the significant substance of any liquid will pull the subsequently scattered molecules from all the different directions. But since surface molecules do not tend to have molecules on their side, they get pulled inwards, which causes the liquid to decrease its size and form a surface with a restricted area and thus into a sphere. This is one of the main reasons water droplets are spherical. One will also notice how water molecules will come together on wax paper because of the higher surface tension than the adhesive forces between the water and paper molecules. Because of the surface tension of water, it allows objects heavier than water to float right over it.

Meniscus

The meniscus is the curved surface of any liquid container. Whenever the cohesive forces among the liquid molecules are higher than the adhesive forces between the wall of a container and the liquid, the liquid’s surface is convex. An example of a liquid in a convex container is mercury.

When the cohesive forces among the liquid are less than adhesive forces working between the container and the liquid, the surface of the liquid curves up; an example of liquid in a curved up surface in a container is water in a glass container.

Suppose both adhesive and cohesive forces are equal between the liquid molecules than the container, the surface of which is horizontal. An example of equal cohesive and adhesive forces is distilled water in a silver container.

Capillary action

A Capillary action results from adhesive and cohesive forces in liquids inside a narrow space like a tube. Whenever a liquid is being out in a narrow space, both cohesive and adhesive forces work together to force the liquid to travel up the space. As a result, it gets lifted against the natural force of gravity.

Application of cohesive and adhesive forces

The ability of adhesion is used for the effective functioning of cement, glue, ink and even glue. Cohesive and adhesive forces induce capillary action, which is a principle for lamp wicks. Wicking is used in synthetic fibre to remove skin’s sweat.

Conclusion

Cohesion and adhesion are properties that determine the working of water daily everywhere, from human bodies to plants. Cohesion is when water gets attracted to water, while adhesion is when water gets attracted to other substances. Cohesion makes water droplets look spherical and creates surface tension where the water molecules attract one another. Thus, the cohesive properties of water explain the property of surface tension in water. On the other hand, the adhesive property of water explains the capillary action when water is being put in a narrow space. Capillary action allows water to flow against the direction of gravity due to its binding with the polar or charged particles.