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Surface Tension

Surface Tension

Surface tension is the property of water to act as a thin elastic membrane at its surface due to intermolecular attraction forces. Surface tension is measured in N/m.

From the word itself we can understand that surface tension is the tension force on the surface of any molecule. This tension arises in every fluid, whether it is water, oil, compressed gas, etc. But water only has the highest surface tension among all the liquids. Thus water is mostly taken to experiment with surface tension or in areas where surface tension is used to demonstrate some values. 

What is Surface Tension?

The tension force on the surface of a liquid formed by the attraction of particles on the surface layer and inside the bulk of the liquid, which minimizes liquid’s surface area, is known as surface tension.

Newton per meter (N/m) is the SI unit of surface tension.

Formula for it is:

Where,

= Surface Tension

F = Force

L = Length

Let us understand it with two examples.

First, when a water droplet falls on the leaf of some plants. They form a curvature without sticking to the surface of the leaf. And they travel on the leaf-like they’re rolling like tires or sphere balls. The phenomenon involved in this is that, as the water droplet falls on the leaf. The water molecule tends to attract each molecule together due to cohesion. Thus, molecules from all sides attract each water molecule and try to form a round sphere. But due to gravity, there can be the possibility of them being in an elliptical shape.

Another example is that we see some small insects floating on the surface of stored water in ponds. This is happening due to the surface tension of liquid again. Water molecules try to attract each other inside the pond and on the surface of the pond. Due to this small insect’s legs do not submerge under the water and they can walk on water.

Understanding the phenomenon of surface tension:

The two major forces involved here are, first, the inward attraction force of water molecules due to which liquid contracts, and second, the tangential force on the surface of the liquid which forms surface tension. And the overall effect of both these forces is that on the surface of liquid it seems like an elastic membrane has covered it.

Due to cohesion (property of molecules to stick together), the molecules in the water attract each adjacent molecule. This attraction from all sides results in net-zero force production. And since the molecules on the surface do not have adjacent molecules on all sides of them, they are attracted to the sides adjacent molecules are present. i.e, inwards. This attraction creates small pressure inside the water bodies and forces the surface of the liquid to contract and occupy as minimum area as possible.

This is the reason behind the formation of liquid droplets as spheres if no other forces are acting on them. And also we can see high surface tension in water when compared to other liquids because water contains hydrogen bonds.

What are the effects of this surface tension in the environment?

As already said in the examples above, floating tiny insects and other dense and light particles on the surface of the water.

Drop formation when liquid bodies are stretched. Such as falling from a height.

Beading of water on a waxy surface. Since water is repelled from the waxy surface therefore we can see small droplets of water forming a complete sphere on waxy leaves or surfaces.

If we mix a little water with oil. Water will form circular or similar to circular shapes on the surface of the liquid.

Formation of the concave and convex meniscus.

Conclusion

To sum up, surface tension is the property of the liquid to make its surface show like a stretched membrane. And this happens because of the attraction between molecules of the liquid. In water, this attraction is there because the formation of hydrogen bonds and surface tension is larger in water than in any other liquid. Due to this property, water always falls in the form of droplets, small tiny insects can float on water, and when on any surface water always try to occupy a circular planform. This surface tension force is very small because heavier dense objects easily get submerged inside the water and lightweight tiny insects and razor blades like substances can float on water without getting submerged in it.