 Why do we feel cool when we sweat or why does water remain cool when it is in this clay pot or earthen pot? Well, turns out both of these are related to evaporation and its cooling effect. And in this video, we will explore what is evaporation and how does it create a cooling effect? So if you have some water lying on the floor or anywhere, the water starts disappearing after a while. That happens because liquid starts transforming into gas. So evaporation is a change of liquid into gas and it can really happen at any temperature. Just that the speed or the rate at which evaporation happens does change with temperature. So evaporation is the change of liquid into gas, change of liquid into gas. Now when we zoom in and try to understand what's happening at the particle level, so let's say we have this container, there is some water in it and there are these particles which are moving around randomly at any speed. So all of these particles are moving at different speeds. Now this body of, let's say, it's water, this body of water, it has a certain temperature of its own. And the temperature really is, the temperature is the average kinetic energy, the average kinetic energy of these molecules, of these molecules. So all of these molecules, they are moving with different speeds, which means they have different kinetic energy. So there will be an average kinetic energy and that really determines the temperature of that body of water. Now molecules near the surface of this liquid, the molecules near the surface of this liquid, they can collide with the air molecules, the air molecules and in collision, they can gain enough energy so that they are able to break these forces of attraction between them. So for instance, let's say this molecule collides with some, with one of the air molecules and in turn it gains enough energy so that it can break the intermolecular forces, these forces of attraction which it has with other molecules and is able to escape, is able to, is able to escape from the surface of the water. When it does so, it changes into vapor. And what really happens when, when the molecule with a lot of energy, with a molecule with a lot of energy, so the molecule that escapes has a lot of energy or the highest energy. What happens when the, when the molecule with the highest energy escapes? Turns out the average kinetic energy of the remaining molecules, it decreases, which means the temperature decreases. So let's try to understand this with a simple, simple maths example. Let's say we have three numbers, we have four, five and six. Right now the average of these three numbers would be five, right? Four plus five plus six divided by three. Now when you remove, when you remove six, the highest number, the average now becomes 4.5, it decreases, it decreased from five to 4.5. Similarly, when the, when the molecule with the highest kinetic energy or the speed, it leaves the body of water. The average kinetic energy of the remaining liquid, the remaining water decreases. Which means the temperature decreases. And this is what creates a cooling effect. This is how evaporation can create a cooling effect. So when there is sweat, that is mostly water on our arms, it's taking heat from a body and evaporating, which is leaving a body cooler. Similarly, when there is water inside clay pots, these clay pots are porous, which means they have small spaces in between them. So water starts seeping through, comes, comes to the boundary of the clay pot. It forms a kind of film, film, a very thin film of water. And then it starts evaporating because it is in contact with the air around it. As it starts evaporating, the remaining liquid inside the pot, it becomes cooler.