Subtitles section Play video Print subtitles It's AumSum Time. How do some insects walk on water? They do not walk. They catwalk. No. Water has an unusual property. What is that? Each water molecule is attracted by other molecules around it in all directions. But since the molecules at the surface have no molecules above them. They get attracted inward more strongly. These inward forces of attraction create surface tension. Thus, making the surface act like a stretched membrane. Now, the weight of insects like water strider and fishing spider is very less. So, the force that the insects legs exert on the stretched water surface is lesser. Than the surface tension. Also, as their legs are spread wide apart. Their weight gets further distributed among all the legs. Hence, the insects' legs do not sink. And just create dimples on the stretched water membrane. Helping it walk on water. Nuclear fusion. Why is nuclear fusion not used to generate electricity? You really want to know the answer to this, right? But wait. Before answering the question, let us understand what is meant by nuclear fusion. When two lighter nuclei combine to form a heavy nucleus. A large amount of energy is released. This process is called nuclear fusion. Where does this nuclear fusion take place? You think that it takes place in a laboratory? No, you are absolutely wrong. Nuclear fusion takes place in the sun. The nuclei of two hydrogen atoms join together to form a heavy nucleus of helium. With the release of a large amount of energy. How do you think this energy reaches us? No. It does not reach us through power lines. Wait, I will tell you. The energy released after nuclear fusion reaches us in the form of sunlight. Ultraviolet radiations, heat, etc. Hey. But we are already producing electricity with the help of nuclear fission. So, why do we require nuclear fusion? For this, you need to first understand difference between nuclear fusion and nuclear fission. As we already know, nuclear fusion is the fusion of two lighter nuclei. With the release of a large amount of energy. The exact opposite process happens in nuclear fission. Here, a heavier nucleus splits into two lighter nuclei, releasing a large amount of energy. This process of fission is used in nuclear power plants. Where a heavy nucleus of uranium is split into lighter nuclei. The energy that is released in this is used to generate electricity. However, there is a major disadvantage of nuclear fission. Wondering what it is? The major disadvantage is that uranium is a radioactive element. When uranium undergoes fission, it generates radioactive waste along with energy. This radioactive waste is very harmful for most lifeforms and the environment. Hence, we need to find a clean and safe source of energy to generate electricity. What source would that be? Would it be nuclear fusion? You are right. Then why are we not harnessing the energy of nuclear fusion to produce electricity? This is because, for nuclear fusion, two conditions are required. They are high pressure and high temperature. Only when these conditions are met, can the two nuclei travel at very high speeds. Resulting in collision. On earth, it is extremely difficult to create such high pressure and temperature. Even if we are somehow able to create these conditions. The question is how will we control them? As there are many questions unanswered and unsolved. We have not yet succeeded in using nuclear fusion in the production of electricity. Heat. Why is a laboratory thermometer not used to check body temperature? You have got fever. Why don't you check your body temperature using a thermometer? No. Please do not use a laboratory thermometer. You will not be able to get the correct reading. Why don't you try another one? This is called a clinical thermometer. A clinical thermometer is different from a laboratory thermometer. Seems like you have made your choice. A clinical thermometer has a kink. When we check our body temperature, the kink present in it prevents the mercury. From falling back down, thus helping the thermometer to hold the temperature recorded by it. And giving us an accurate reading. Now, in a laboratory thermometer, this kink is absent. This is because a laboratory thermometer is meant to measures immediate temperature. Hence, after recording our body temperature, until we check it, the mercury will fall. Thus, not giving us an accurate reading. Ultrasound. Why is ultrasound used in sonar? Hey. Looks like you are searching for a treasure hidden in a sunken ship. Why don't you use a sonar? It will emit ultrasounds and help you locate the ship. You know what, I have a better idea. No. A music system will make ordinary sound. So, it is of no use. Do not fool me. I know that the music system is the right choice. See, you are not able to find the ship. Now, will you use a sonar? Look, you easily found the ship. Do you know how a sonar could locate the sunken ship? It was because of ultrasound. Ultrasounds are sounds having very high frequencies which start from 20,000 Hertz. So, is ultrasound used in sonar because of its high frequency? You are absolutely correct. Due to its high frequency, an ultrasound can penetrate to a greater depth. Thus, helping us to locate the depth of the sea, sunken ships, etc. But, I am not able to hear the ultrasound? It is because human beings can hear sound frequencies from 20 Hertz to 20,000 Hertz. As ultrasounds have frequencies higher than 20,000 Hertz, we cannot hear them. Bad conductors of heat. Why are two thin blankets warmer than one thick blanket? Because two chocolates are better than one. No. To understand this, we need to first learn about bad conductors of heat. Bad conductors of heat are the materials which do not allow heat. To easily flow through them. Air, wood and glass are some examples of bad conductors of heat. In these examples, is our train conductor included as well? Just listen. A thick blanket allows much of our body heat to escape into the atmosphere. However, when we use two blankets one on top of the other. Air gets trapped between them. This air being a bad conductor of heat, does not allow our body heat. To easily flow into the atmosphere, thus keeping us warm. Pathogens. Why do we get fever? So that we can take a holiday from work. No. Fever is a protective response of our body to fight against pathogens. Such as bacteria, viruses and fungi. These pathogens cause diseases. Hence, when pathogens enter our body, the immune cells such as white blood cells. Produce chemicals called pyrogens which are released into the bloodstream. I thought like movies, they are released in theaters. Please, pay attention. Hypothalamus, which is a small part of our brain, regulates our body temperature. However, when these pyrogens reach the hypothalamus, it starts to raise our body temperature. Thus, producing fever. Now, one of the reasons for producing this fever is that many pathogens. Cannot survive at high temperatures. Thus, they die and we remain safe. Human tears. Why do onions make you cry? Because they cannot crack a joke. No. Onions consist of amino acid sulfoxides. When we cut an onion, millions of onions cells rupture. Releasing the amino acid sulfoxides along with some special enzymes. These special enzymes react with amino acid sulfoxides. To form a chemical called Syn-propanethial-S-oxide. This chemical is volatile, that is, it easily evaporates at normal temperature. Forming a gas. When this gas reaches our eyes, it reacts with substance that keeps eyes lubricated. And forms mild sulfuric acid. What? An acid in my eyes. Absolutely. This sulfuric acid gives us a burning sensation. Now, in order to wash off this acid, our lacrimal glands produce a disinfecting liquid. But when our eyes cannot hold any extra amount of disinfecting liquid. It starts to fall down, making us cry. Joints. Why do knuckles pop? So that when we get bored we can pop them for time pass. No. A knuckle is a joint in the finger where two bones come together or connect. This joint is filled with a fluid called synovial fluid. Synovial fluid is a viscous fluid containing dissolved gases like oxygen and carbon dioxide.