MHT-CET 2027 | Surface Tension The Secret Of Water

[00:00:00]When you see a rain drop or a soap bubble, think about why this sphere is there. Surface tension force per unit length is known. It seems that surface tension is known.

[00:00:13]Hello, today we are going to talk about surface tension.

[00:00:16]Children who are studying in class 18 to 12 know what the concept is. Many children memorize the formula of surface tension. Surface tension force per unit length is known. It seems that surface tension is known.

[00:00:28]Numerical solutions are given to us. Sir, surface tension is known to us. But do you really know surface tension?

[00:00:33]If you think about it conceptually, ask yourself what surface tension is. See if you can answer the same question.

[00:00:41]Surface tension is a surface phenomenon and the first thing we observe is surface tension in liquids.

[00:00:48]Liquids contain molecules. The first thing you should know is that molecules are in gases or in liquids. For example, hydrogen and oxygen are very far apart from each other at a certain temperature in a gas, but when we liquefy them, when the liquid form is formed, the molecules stick to each other due to the forces of attraction called molecular intermolecular forces. They attract each other and when they attract each other, they are not so attracted that they are solidified. There is still a little gap between them and there is a certain degree of freedom between them.

[00:01:24]Therefore, when the liquid form is formed, the molecules themselves move here and there. Now, what is happening inside the surface? Suppose we take a liquid. The molecule inside is attracted by all the molecules around it.

[00:01:40]But the molecules on the surface are not the only ones that attract them. They are forced inside. On the outside, there is air, so the air is the only one that is attracted. That negligible amount of liquid inside it is called liquid attraction, so due to liquid attraction, the molecules that are forming on the surface are all pulled inwards and when all the molecules try to go inside, they all get pulled inwards. Well, the liquid molecule that is in the liquid molecule has no issue, it is pulled inwards equally everywhere, so it is sitting perfectly still, but the molecules on the surface are pulled inwards and due to being pulled inwards, a tension is generated somewhere on the surface, like if you put an object in a plastic bag, how does it become like this?

[00:02:26]But if you pull that plastic bag from all sides with force, what will happen is that it will become tight and now if you put a small stone on that tight bag, the bag will not bend or move a little, but it will balance the stone. A tension is created in the surface.

[00:02:41]This tension is created due to the tension that is created. If you place a small object on it, the needle is a needle.

[00:02:49]If you place that needle on water, then the needle becomes steel. The density of steel is about 10 times that of water. It is seven times heavier.

[00:03:01]Although the density of the needle is 10 times, the needle does not sink in water. It floats.

[00:03:05]Surface tension makes the needle float. If you stand it upright, it will go inside. But if you place the needle slowly and very gently in the water, it floats. Mosquitoes walk on water.

[00:03:14]Small insects can walk on water. This is the reason why this surface tension is because the force of attraction on the surface is very low. All the molecules try to go inside.

[00:03:29]Therefore, the surface is in a state of tension. It is attracted everywhere. Because of this, it is attracted to this liquid. Tension is generated and you should know that this tension in a liquid, which has a tendency to go inward, is trying to reduce the area of ​​the liquid. Continuously, if you put even a small drop of water, it will become round because the reason behind becoming round is surface tension. Why are rain drops spherical? Why are soap bubbles spherical? This is the reason why surface tension exists because every liquid molecule has to go inward because it cannot be stable or unstable. It has to be unstable because a molecule on the surface is unstable because it only needs an internal force to be pulled inward. It is pulled inward and then it will go inward and then it will become stable. But the problem is that if everything goes inward, then who will make the surface? To make a surface, there must be a minimum number of molecules on the surface and those who are at least will make a surface that has a minimum area.

[00:04:20]Therefore, the liquid will never be able to move on its own. It will try to reduce the area.

[00:04:24]So, if you ever see a rain drop or a soap bubble, think about why this sphere exists.

[00:04:29]Surface tension is the reason. Thank you.