 Hi, I'm Zor. Welcome to Unisor Education. Today's lecture is about energy of Nucleus. And this lecture is part of the course called Physics for Teens, presented in Unisor.com. I do suggest you to watch this lecture from the website Unisor.com. You have to go through Physics for Teens to energy and then there is a nuclear energy chapter in this. Because every lecture on this website has a textual detailed notes, which basically can be used as a textbook. And then, well, it's the course. I mean, on the website, it's the course. It has certain chapters. It has logical connection between different parts, different lectures. It's not like you just found one particular lecture on YouTube or somewhere else, and it's just by itself. It's not. This is the course, and I do recommend you to take the whole course. Plus, on the same website, you have a prerequisite course called Math for Teens. You know, Math is the mandatory part of the physics course, so I do suggest you to be relatively proficient in Math, in particular, calculus, vector algebra. That's all important. All right, so today we'll talk about nuclear energy, but I would like to start from a couple of previous lectures where we were also talking about energy. They're all related between themselves. We started with mechanical energy, which is energy of the macro objects moving or positioned against each other. That was our first kind of introduction to energy topic. Our next one was related to looking into the macro objects to see what are the smallest parts of any object, which is still maintaining its characteristics, and this is a molecule. A molecule of water is still a water, but anything less than the molecule is already not a water. Whenever we are talking about the molecules inside the macro objects, molecules are moving, and the moving of these molecules is a next type of energy, which we were talking about, the thermal energy or heat. Okay, so let's go even deeper than that. What happens if we will go inside the molecules? Well, molecules contain atoms inside, so basically any kind of a combination of atoms make a molecule. Now, there are only about 100 different atom types, but the number of molecules is tremendous, like thousands or millions. That's different types of substances we are dealing with, and now from all these atoms we can create the molecules. So, something like 100 different types of atoms combined together in different quantities make all the millions of molecules. Now, so what happens with the next level as we are going inside the molecule to the atomic level? Well, there is a chemical energy, that's the next type of energy, which we were talking about. So, as we go deeper inside the objects, the molecules, to the atoms, we are uncovering different types of energy. So, chemical energy is the energy which is related to atomic bonds. So, whenever we are breaking some molecules into individual atoms and combining into other molecules, this is the process which is called chemical reaction, and rearranging the atoms either consumes or releases energy. Now, let's go inside the atoms. This is our last movement towards the depths of the matter, how the matter actually is organized. So, what's inside the atoms? Well, the very simplified and I would say very classical model of atom is that atom contains three kinds of particles. Two heavy ones, proton and neutron, combined together in different quantities make up nucleus of the atom and electrons are orbiting around this nucleus. Now, protons and electrons are electrically charged particles, positive and negative correspondingly. Neutrons are electrically negative. So, this is the model of atom. So, in this simplified model, again model, it's not what's happening in reality. I don't know what's happening in reality, but this is a good model. It allows us to do a lot of different things which basically correspond to our experimental data. So, from only these three types of particles, at least as it was known in the beginning of 20th century, we combine them together into about a hundred different atoms. So, what actually is happening? Well, different number of protons and neutrons make certain nucleus, and then number of electrons in electrically neutral element should be equal to the number of protons, plus and minus, right? So, they are neutral. So, the only difference between all these 100 different types of atoms is the number of protons and neutrons inside the nucleus. And, obviously, electrically neutral number of electrons probably should be equal to number of protons for electrically neutral elements. Now, very similarly to chemical energy related to chemical reaction, which is actually rearranging of atoms into different molecules. Same thing with nuclear energy is related to nuclear reaction. Whenever we are rearranging protons and neutrons which are making some atoms into different atoms. So, again, we can break, for instance, the molecule into individual atoms, regroup them to get another molecule. That's the chemical reaction, and the energy is either released or consumed. Same thing here. We are breaking atoms into individual protons and neutrons, reconfigure, regroup them together into different atom, and as a result, we will get either consumed or released certain amount of energy. So, this is a general hierarchical view of different types of energy, as we are going deeper and deeper inside the matter. So, we have mechanical, we have thermal, we have chemical, and nuclear energy. All right. So, that's a good introduction. Now, next question is, well, we know, and if you don't just believe me, that there is electrical component in the construction of the atoms. I was talking about positively charged protons and negatively charged neutrons, sorry, electrons. Neutrons are neutrally charged. There is no charge inside the neutron. Now, the opposite electrically positive and electrically negative particles, electrically charged, they are attracting each other. So, this is a good question. Similarly charged, like proton and proton or electron and electron repel each other. Well, this is the nature of electricity. We will talk about this whenever we will consider the electricity. But in this particular case, this is just something which is, well, you can say, the law of nature or whatever it is. Now, knowing this, the question arises. What keeps protons and neutrons together in the nucleus if, let's forget about neutrons for a while, but protons are repelling each other. So, why doesn't nucleus just fall apart into different protons and neutrons? Why is it together, like, 50 different neutrons and 48 different protons together? They are forming a nucleus of some element. I don't remember which one. It doesn't matter. Okay. So, there is very important consideration and, well, basically physicists were thinking about this. They knew electricity. They knew that the protons are positively charged and they must repel each other. So, something holds them together. What? Well, the answer is there is yet another force in the nature. Not only gravitational force, not only electromagnetic force. There is also some other force which is called strong force. Now, why is it called strong force? Well, the answer is actually obvious because it should be stronger than electricity because the protons together, if they want to stay inside the nucleus, there must be something which keeps them together. That's what keeps them together, the strong force. So, the strong force is stronger than electrical repelling force and that's why the nucleus actually doesn't fall apart into individual particles. The only thing which is kind of different, well, it's important to put it this way. Strong force acts, if this is the proton and this is the proton, it acts between them. This is the positive and this is the positive. It actually acts on a very, very short distance. If two protons on a bigger distance, the strong force, so it's not really strong enough. So, the strength of the strong force is increasing as we are moving closer and closer and obviously decreasing if we are moving them apart. Now, the law of changing the strength of the strong force is such that on a longer distance it's practically undetectable. But in a short distance, a very short distance, very much comparable to the nucleus size. The strong force is significantly stronger, like a hundred times stronger than the electrical force of repelling from each other. So, to keep the protons together, well, and neutrons as well, because there is a strong force between all of them, to keep the nucleus together, we have to really move all these particles very close together and then the strong force will really catch them up. Because if they are really apart, then the strong force is not really strong enough and the electrical repelling would probably be stronger to force the particles to go into different directions. Alright, so, we have introduced a new concept, a strong force, which keeps the nucleus together, which means that if we want to reorganize the atom, we have to somehow break some strong forces and rearrange them into a different configuration so other strong forces will take hold. So, this is the source of nuclear energy. So, in some cases, if we are doing certain nuclear reaction, the overall energy is released, in some cases it's consumed. It's exactly the same as in the course of chemical reaction. We are either releasing or consuming certain amount of energy, depending on what exactly we are doing. So, let's just think about what exactly can happen in what cases. Let's consider that we have an atom of hydrogen. It has a proton and it has an electron and an orbit. So, this is positive one, this is negative one, and that's why the whole thing is basically electrically neutral. Now, there are different isotopes, if I can say, of hydrogen. This is a regular hydrogen. There is a deuterium of hydrogen, which is a hydrogen of hydrogen, which is a hydrogen which has neutron as well. Now, what happens if we will combine proton and neutron to make an atom of deuterium? Well, think about it this way. There is a strong force between them, right? Let me just give you an example. Let's say we have an object above the Earth and then we dropped it down. What happens? Well, at this position, it has certain potential energy, right? Whenever we drop it down, it hits the ground and it has no more potential energy. So, where is the energy going? Well, the energy will be converted into probably some kind of a thermal energy because we are squeezing the molecules of the ground, so probably they are heating a little bit or something like this. So, the kinetic energy of these pieces of the ground, which we are heating with our object, whatever conversion is, but it happens and the potential energy here is converted into other kinds of energy, which is released. It's like thermal energy or kinetic energy, whatever it is. It's released and our object is on the surface of the Earth anymore. It does not have any potential energy. Now, what happens if our proton and neutron are at certain distance from each other? Well, in this case, there is no electricity among them, right? Because the proton is positive, but neutron is neutral, so there is no electrical force in between. So, the only force is the strong force. Yes, granted, it actually acts in a very small distance, but what does it mean? I mean, whenever the distance is greater, it still acts, but it's weaker. Same thing like the gravity. Gravity on the surface of the Earth is stronger than if we will go up, let's say, 1000 kilometers up from the Earth and the gravity will be smaller, right? Remember, the gravity is actually decreasing with the distance, inversely proportional to the square of the distance between the centers. Here is the same thing. It's just not the square proportional or inverse proportional, but there is definitely some kind of potential energy, because there is an attraction between them. The strong force is the force of attraction. So, there is a potential energy. Now, so what happens if we are making them closer together, if they fall on each other? Well, there is no more potential energy, right? So, where is the energy? Well, whenever we are moving proton and neutron or rather the atom of hydrogen and add the neutron into this so that the neutron and proton will combine together because of the strong force, potential energy which they had before they are together when they are apart must be converted into some other form of energy and released, obviously, the same thing as if I will drop something on the floor, the potential energy is converted into kinetic, thermal, whatever it is. So, here is exactly the same thing. So, some form of energy, thermal energy, electromagnetic, I don't know, whatever it is, it should be released in some way or another, which means that by doing this we can actually release certain energy. So, this is a nuclear reaction combining proton and neutron together to form the atom of deuterium produces certain amount of energy. That's very, very important. There is one more very interesting thing and it's related to theory of relativity which I know we didn't go yet, but everybody knows a beautiful formula which is actually the most famous formula in physics. The energy is equal mass times square of the speed of light. So, energy and mass are always related. If we have certain particles and then we have a nucleus which contains these particles but certain amount of energy has been released, what does it mean? Well, it means that we have lost certain amount of mass as well and the mass of proton plus mass of neutron should be greater than the mass of proton plus neutron. This is called defective mass and it is indeed true. The sum of two masses is greater than the mass of the nucleus of deuterium in this particular case. So, and that's because energy is always related to mass. Since we have released certain amount of energy, used to be potential energy, now we don't have it. So, it's released in some form or another which means we have lost certain amount of mass. Now, let's think about bigger atoms. This is an atom of hydrogen and there are only like two particles inside the nucleus, proton and neutron. What if you have bigger atoms? Well, bigger atoms have more protons and if you would like to combine two different atoms like, for instance, atom which contains 15 protons plus 14 neutrons and combine it with 12 protons and 10 neutrons. If we will combine these two nucleases together, what happens with energy? Well, that's not such a simple answer because don't forget that since there are protons here and here, they are repelling each other. So, it's not so much, you know, it's not as easy as in this particular case to combine them. It's not as clear now because the energy we have to really combine whatever the potential energy these two have when they are apart should actually be somehow compared with repelling energy which is also a potential energy. If two things are together, we are holding them together using something but they still have a potential energy because if we will break the link, break the strong force, then they will just fly apart. That's a potential energy like a spring. The compressed spring has a potential energy. So, in this particular case, if we will combine them into one nucleus, they would have potential energy inside as an electrostatic repulsion. So, it looks like if we have bigger atoms, it's not really obvious whether the potential energy of the strong force when they are apart is bigger or smaller than potential energy of the electrostatic repellent when they are together. So, what's the final equation? What's the final result? Whether energy will be released or consumed depends on comparison between the potential energy of the strong force when they are apart and potential energy of the electrostatic repelling when they are together. So, the calculations show that as we are combining bigger and bigger atoms, in the beginning when we have very few number of protons, the final result will be releasing the energy. But at some moment as we are dealing with greater and greater atoms, it becomes the other way around. Somewhere on the level of iron, the atom of iron, we have this borderline when it's almost the same thing. So, lighter than iron atoms probably will release certain amount of energy and heavier will consume. What it also means that the opposite process, if we will break the nucleus into parts, if we will break the small one, we will have to actually consume certain amount. But if we will break the bigger ones where the electrostatic energy is significant potential energy of repelling and we will break the strong forces so we will let this spring which basically imitates the electrostatic repelling, if we will let that spring to go, that would release. So, the heavy atoms produce energy if we split them. The light elements produce certain amount of energy if we make them from their own parts, particles rather. And these are two very, very important processes in nuclear reaction. This process is fusion when we are fusing together and the process whenever we are breaking the big atom into its pieces. It's called fission. And both are the processes where we can use this energy produced by these reactions. So, whenever we are fusing certain light atoms, we are producing energy and it's used in hydrogen bomb, unfortunately. Now, whenever we are splitting the heavy atoms like plutonium, for instance, we are producing energy which is the fission reaction so this is where the atomic bomb, the first bombs actually were invented and later on we have learned actually how to control this nuclear reaction of fission and we use them in nuclear power plants. Using the fusion to produce electricity in some kind of power plants is kind of questionable right now. I mean, there are experimental processes but it's still experimental. Now, the fission is very much used all over the world. Nuclear power stations are used everywhere. Unfortunately, we had certain disasters. We had Chernobyl disaster and we have in Japan Fukushima disaster. So, probably the work should be done to make it much safer than they are right now. But anyway, the number of nuclear power stations is really very, very large and we can use relatively safely this nuclear energy. There are some other issues with the result of this splitting. It's not so easy. I mean, we will talk about the details, what exactly is fusion and what exactly is fission, what exactly components which are produced when we are making one reaction or another reaction. But as of right now this is an introductory lecture to nuclear power, nuclear reaction, the energy of the nucleus. That's probably sufficient information. So, light atoms can produce energy if we fuse elementary particles or parts of these atoms and the fission is used when we are splitting the heavy atoms like plutonium or uranium or whatever. Okay, so that's it for today. That's kind of an introduction into what nuclear energy is and where it stands in the hierarchy of different energies. I do suggest you to read the textual part. There are some interesting numbers about the strengths of the strong forces relatively to electrostatic ones. It's all on the website Unisor.com in the physics 14 course. So, thanks very much and good luck.