 So why did the food colors move this way? When we kept the container full of water on top of the mug with warm water, that heated up the middle part of the container. It heated the water in the middle part and the water on the sides of the container was at room temperature or cooler than the water in the middle. Well, okay, water in the middle is warm, but why does it rise? Well, turns out it rises because it becomes lighter than the surrounding water. When water is heated, it becomes lighter and begins to rise. The same is true for air as well. When air is heated or warmed up, it becomes lighter than the surrounding air and begins to rise. We can see that whenever we see steam, you always see steam rising upright because it is warmer and lighter than the surrounding air. Similarly, the water in the middle gets heated, becomes lighter and begins to rise and as the warm water rises, it takes the red food coloring with it, which is why we see the red color rising. Now as the water in the middle rises, water from the sides starts to take its place in the middle. Therefore, we see the blue food color move to the middle. Finally, when the water from the sides moves to the middle, it starts getting warmed up and begins to rise as well, which we finally see in the blue food color rising up. Then again, the water from the sides and the top, which got some time to cool off, will move to the middle, get heated and again, it will rise. In this way, all of the water is heated and this method of heat transfer is called convection. In this method, the entire material moves. Here, water itself moves and we can see that through the movement of food coloring. Now, convection is not just limited to water. We see convection even in air. Warm air rises up, cool air sinks down. You must have seen exhaust fans attached near the top of the rooms, right? Why are they attached at the top and not in the middle or bottom? Well, turns out our body heat and maybe TV or fridge, all of these appliances are heating up the air around us, because of which it rises to the top of the room. And if there is an exhaust fan, it can then be removed and to take the place of the warm air, cool air from under the doors or windows come inside the room. So, an exhaust fan not only helps remove bad smells, it also helps to keep the indoor air slightly cool. We also see convection in chimneys. In a furnace, when things are burned, hot smoke rises up and is released outside through a chimney.