Subtitles section Play video Print subtitles Smart Learning for All. Topic: Tyndall Effect. Why does the sky appear blue? It is such a beautiful rainbow. Have you ever wondered, how it is formed? A rainbow is formed when raindrops split sunlight into different colors. Sunlight or white light consists of many colors. However, only a few of them are visible to us. A band of these visible colors is called a visible spectrum. When we see a rainbow, our brain and eyes distinguish the visible spectrum into seven main colors. Namely red, orange, yellow, green, blue, indigo and violet. Did you notice that the size of the balls increased? Yes, you guessed right. The balls represent the different colors of a rainbow in increasing order of their wavelengths. Wavelength is the distance between consecutive crests or consecutive troughs in a wave. In a rainbow, as we move from violet to red, the wavelength of colors increases. Violet has the shortest wavelength while red has the longest wavelength. Do you think that our eyes have a natural inclination towards blue as compared to violet? Yes, this is one of the reasons why our sky appears blue and not violet. To understand this, first let us study about Tyndall effect. Tyndall effect is a phenomenon in which a beam of light scatters on striking the particles present in its path. This scattering of light is responsible for the blue color of the sky. We know that our atmosphere primarily consists of oxygen and nitrogen particles. Along with dust, smoke and other particles in comparatively smaller proportions. The size of these particles in the atmosphere is responsible for the color of scattered light. When the sunlight strikes particles of dust,smoke, etc. Which are bigger than the wavelength of sunlight, all the colors of sunlight are equally scattered. As a result, the scattered light appears white. However, when the sunlight strikes particles of oxygen and nitrogen. Which are smaller than the wavelength of sunlight, the colors of sunlight having shorter wavelengths. Blue and violet are much more scattered than colors having longer wavelengths. But our eyes are much more sensitive to blue color as compared to violet, hence the sky appears blue to us. Topic: Density. Why does oil float on water? Did you realize that a large log of wood floated on water but a comparatively smaller piece of rock sank? How is this even possible? This is possible because of density. It is the measure of the mass of an object per unit volume. In the first case, the log of wood floats on water because it has less density than water. This means that the amount of mass present in unit volume of wood. Is less than the amount of mass present in unit volume of water. However, in the second case, the piece of rock sinks because it has more density than water. This means that the amount of mass present in unit volume of rock. Is more than the amount of mass present in unit volume of water. Do you know why the helium filled balloon is rising up in the air? This is again because of density. The balloon consists of helium gas which has less density than the surrounding air, hence it rises up. Here, have a look. Oil is floating on water. Are you assuming that this is because of density? Yes, you are right. Oil has less density than water. Hence, it floats. However, there is another reason due to which oil floats on water. The reason is that both oil and water are immiscible liquids. They do not mix with each other even if we shake them. They separate out into two layers when kept undisturbed for sometime. Topic: Centrifugation. How is the principle of centrifugation helpful in blood banks? Do you know that jelly is a colloidal solution? A colloidal solution is a solution whose particles neither dissolve nor settle down. Another example of a colloidal solution is blood. Blood consists of various components like red blood cells, white blood cells, platelets, plasma, etc. Which neither dissolve nor settle down. Usually, in blood banks, when a blood sample needs to be tested, its components have to be separated. So, how can we separate those components? What do you think? Can we use a filtration technique to separate various components of blood? No, filtration is not useful because the size of the components of blood is so small. That they can easily pass through the filter paper. Similar to this merry go round. A machine called centrifuge is used in blood banks to separate blood components. In the centrifuge machine, a test tube filled with a blood sample is rotated at a constant high speed. This process is called centrifugation. Centrifugation is based on centripetal acceleration. Due to centripetal acceleration, the heavier components, that is, the red blood cells move outwards. The white blood cells and platelets which are lighter than red blood cells form the middle layer. Plasma being the lightest moves towards the center. In this way, components of blood get separated by the principle of centrifugation. Topic: Balanced and Unbalanced Forces. How are we able to stand on the earth without falling into the center of the earth? Hey. That was a nice balancing act. Do you know there are certain forces around us which keep us balanced or unbalanced? Force is a push or a pull exerted on an object. Every object on the earth experiences various forces. When a number of forces acting on an object are such that their resultant force is zero. Then the forces are said to be balanced. Whereas, when a number of forces acting on an object are such that their resultant force is not equal to zero. Then the forces are said to be unbalanced. When he was falling which forces were acting on him? Were they balanced or unbalanced? In this case, unbalanced forces were acting on him. On earth, many forces act on an object. One of them is gravitational force of the earth. Gravitational force of the earth is the force which pulls all the objects downwards. Towards the center of the earth. Let's get back to the question. When he was falling, the gravitational force over powered all other forces. So, the resultant force was not equal to zero. We can conclude that unbalanced forces were acting on him. Did you see that? He landed safely. But if the gravitational force was pulling him towards the center of the earth. Why did he fall on the ground and not into the center of the earth? We know that gravitational force is pulling us downwards. However, there is another force exerted by the ground which pushes us upwards. This force is called the normal force. It is equal to the gravitational force. Normal force is exerted by a surface only when we are in contact with it. Since these two forces acting on us are equal but opposite to each other. Their resultant, that is, net force is zero. Thus, these balanced forces keep us from falling into the center of the earth. Topic: Solubility. When you open a shaken cold drink bottle, what makes the fizz explode out? Did he really prepare a cold drink from flavored water and carbon dioxide? Yes. A cold drink usually contains flavored water and excess amount of carbon dioxide dissolved in it. This mixture forms carbonic acid which gives the cold drink a distinctive flavor. Under normal conditions, it is difficult to dissolve excess carbon dioxide in water. Only a certain amount dissolves easily. Hence, to obtain that distinctive flavor. Excess carbon dioxide is dissolved in water under high pressure and low temperature. Due to this technique. The water molecules enclose and trap extra carbon dioxide molecules to prevent them from escaping. Once the excess carbon dioxide is trapped by the water molecules. The bottles are sealed with an airtight cap. This helps maintain pressure inside the bottle and hence, the taste. Do you know why the cold drink tasted flat after keeping it open for some while? This is because when the bottle was opened, the pressure in the bottle was released. The excess carbon dioxide started escaping from the water molecules. After some time, most of the carbon dioxide gas escaped. As a result, the cold drink tasted flat. Hey. That was funny. In reality, when the bottle is sealed, the undisturbed liquid has surface tension. In order to escape, the carbon dioxide molecules require energy to overcome this surface tension. Now, when we shake the cold drink bottle before opening. The trapped carbon dioxide molecules get that required energy. They break free from the liquid's surface tension. As a result, the fizz rises quickly and explodes out. Topic: Thermal Expansion. Why are small gaps left in between rails? Hey. Did you notice that the level of mercury in the thermometer rose when it was placed in hot water? You must be wondering why this happened, right? It happened because of thermal expansion. Thermal expansion is the tendency of matter to expand on heating. This tendency of expansion can be observed in solids, liquids as well as gases. Now let us see how this concept of thermal expansion applies to a thermometer. A thermometer usually consists of a narrow tube with a small bulb at its one end. The bulb and a part of the narrow tube is filled with mercury which is liquid at room temperature. Now, when a thermometer is placed in hot water. Mercury inside it expands due to thermal expansion and as a result its level rises. You must be thinking how the gasoline came out of the tank even though it was exactly filled till the brim. Am I right? Gasoline also expands on heating. So, what happened is that when the tank was filled till the brim, there was no space left in it. Now, when the bike was kept in the sun. The tank became hot which eventually heated the gasoline filled in it. As a result, the gasoline expanded. But since there was no space left in the tank, expansion forced gasoline to come out of the tank. Do you think that the rails bent because of thermal expansion? If yes, then you are absolutely correct. A railway track is made up of a number of rails joined to each other. These rails are usually made up of steel. Steel expands on heating and contracts on cooling. When the rails are joined to one another without leaving any space for expansion. The rails bend due to thermal expansion and the train goes off the railway track. To avoid this, the rails are not joined together firmly. Instead, each rail is connected to the other in such a way that a small gap is left in between them. These small gaps provide space for easy expansion of the rails. Which happens during summer as well as due to continuous friction between the train wheels and the rails. Hence, these small gaps prevent the rails from bending, preventing any kind of accidents. Topic: Mitosis. How does a house lizard regenerate its tail? Have you ever wondered how we grow from a 20 inch new born baby to a 70 inch teenager? This is because every minute millions of cells in our body divide to form new cells. These new cells then further divide to form more cells. In this way, the number of cells in our body increases and we grow taller. Mitosis is a process through which cells in our body divide. Mitosis is used by organisms not only for growth but also for repair, replacement and asexual reproduction. Hey. Were they exact copies of each other? Yes. In mitosis, a parent cell divides to form two identical daughter cells. Both of them have exactly the same genetic material. Hence, they are exact copies of each other. Hey. Did the head of the scarecrow just grow back? Yes. You will be surprised to know that some organisms like a house lizard. Can regenerate their cut or damaged body parts through mitosis. When the house lizard's tail gets cut, it regenerates its tail through mitosis. Each cell around the cut tail starts to divide and forms two identical daughter cells. Again each of these daughter cells further divides to form two more daughter cells. Thus helping the lizard to regenerate its tail. Topic: Atmospheric Pressure. Why don't we get crushed by atmospheric pressure? Hey. Did you hear that? His ears popped. Is this related to atmospheric pressure? Yes. We know that our earth is surrounded by a layer of air called the atmosphere. The gravitational force of earth constantly pulls this atmosphere towards itself. Due to this. The atmosphere exerts a pressure on the surface of the earth as well as on the objects present on its surface. This pressure exerted by the atmosphere is called the atmospheric pressure. This atmospheric pressure outside our body is balanced by the air pressure present inside our body. When the atmospheric pressure decreases, it becomes less than the air pressure inside us. Now, to balance the pressure inside and outside our ears, the air present inside rushes out. Whereas, when the atmospheric pressure increases, it becomes more than the air pressure inside us. So, to balance the pressure inside and outside our ears, the outside air rushes in. This movement of air results in that sudden pop. Have you noticed this before? Has your water bottle ever got crushed once your airplane landed? This happens because of changes in the atmospheric pressure. Generally, the atmospheric pressure in the bottle is equal to that on the surface of the earth. Whereas, in an airplane the atmospheric pressure is low as compared to that on the surface of the earth. During the flight, when you open the bottle and drink some water in the airplane. The atmospheric pressure in the bottle becomes low. This is because the low pressure air present in the airplane occupies the place of water which you just drank. However, when the airplane lands and you come out of the plane, the pressure outside the bottle. The atmospheric pressure on the surface of the earth is high as compared to the pressure inside the bottle. Hence, the outside air exerts a greater pressure on the surface of the bottle than the inside air. As a result, the bottle gets crushed. Wow. How is he able to lift such a heavy car? Are we also powerful enough to handle such a huge amount of pressure? Yes, to some extent we are also carrying a huge amount of pressure. At sea level, the atmospheric pressure is about 14.7 psi. This means that the atmosphere is exerting 14.7 pounds of force on every square inch of our body which is really huge. So, why don't we feel this immense pressure? This is because various parts of our body such as ears, nose, lungs and stomach also contain air. Which exerts pressure on the atmosphere which is equal to the atmospheric pressure. In this way.