 Hi, I'm Zor. Welcome to Unisor Education. Today I would like to talk about units of energy and work. Now this lecture is part of the course called Physics for Teens. It's presented on Unisor.com. That's the website. Right now we are in the very last part of this course where I'm just talking about units of measurement. Now the lectures in the course of this part, well, trying to do it everywhere, but in this part are actually sequenced in a very proper way, which means I first introduce some base units and even within the base units I'm introducing first something like seconds for example, time units, and based on that I introduced some other units. So it's always introduction of the new units based on whatever has been already defined. That's why it's very important to watch these lectures in exactly the sequence they are presented. Now today I will do basically the same thing. I will continue building new units, in this case units of energy, based on whatever we have already covered. Now the website, I prefer actually use the website to watch the lectures because there is a menu and using the menu you can actually maintain the proper sequence of the lectures. So if you just found it accidentally somewhere on YouTube or wherever else, just know that Unizor presents a much better picture of everything because it's a course which was logically constructed based on this gradual incremental knowledge. And the website also contains the prerequisite course called mass routines. Mass is absolutely necessary to start physics. And the website is totally free. You don't even have to sign in if you don't want to. There are no advertisement. There are however certain functionality features. For example, you can take exams as many times as you want until you will get the perfect score. So back to energy. Well, we will start talking about energy and units it's measured with the concept of work. So what is work? By definition, if you have a constant force, force is a vector. So there is a direction and the magnitude. And it forces some object to move in the same direction the force is directed with certain acceleration because the object has a mass and the force acting on mass produced certain acceleration according to the second Newton's law. So as a result, this particular object is moving at a certain distance, let's say s, during a certain time period. Now, by definition, the work which this particular force is performing is equal to force times distance. Now, from common sense, it's obvious that if you will increase by factor of two, let's say, the distance, the constant force is acting. It should increase the work by two. So that's why it's definition is this way. So now, if there is a little bit complicated case, for example, the force is directed at the angle to the trajectory. What kind of work it does? The work, we represent this force as a combination of the force which goes with the direction of the, with the trajectory, direction of the movement, and the perpendicular. And obviously, perpendicular doesn't contribute anything to movement towards this direction. Only this component does. So it's basically original force times cosine of the angle. That's the projection of the force onto trajectory. Still, basically, it's the same thing. Force is newtons. And the distance is in meters. So what was actually decided was that we will introduce a unit and we will call it a joule, which is equal to one newton times meter. So if it's one newton times one meter or half newton times two meters or whatever else, it will give you one joule. So whenever the multiplication of newton force basically in newtons and distance in meters is equal to one, that's the work of one newton. One joule. Abbreviation is J, capital J. So basically one J is equal to one newton times meter. So that's the definition of the unit of work. Now there is even more complicated case when the force is variable, changes everything, direction, magnitude, etc. Well, as we usually do in this case, we divide our trajectory. And by the way, the trajectory also not exactly the straight line, but something like curve. And the force is acting in many different directions. So how to calculate the work there? Well, we divide it into infinitesimal pieces. On each infinitesimal piece of a trajectory, we're considering force to be constant because it's infinitesimal piece of trajectory, whatever it is, and then use exactly the same formula, magnitude of the force, time cosine of an angle with tangential line with our trajectory. That's the force. And the differential of trajectory is the distance and we integrate along this curve. So it's all kind of mathematics and it doesn't really relate too much to establishing the unit of measurement of work, which is one joe. So that's it. We have finished with work. Now these lectures related to units are really very simple ones. All we need to know is what kind of units have already been established and the formula which basically explains the new concept for which we would like to introduce a new unit, how this formula relates this new concept with old ones. In this particular case, the formula was, as I was saying, W equals F times S. That's the original formula. So force have already been defined before. Distance is one of the base units of measurement and this is the work. So this has already been defined in the previous lectures. This has been defined in the previous lectures. That's why we can define this one based on one of this and one of this gives you one of them. So that's always like that. Okay, so let's introduce a new concept. New concept. Now this is work. Now we're talking about power. Power. P. Again, formula. First of all, formula. Now how power actually, what is power? Power is basically amount of work we do in the unit of time. So the formula should be, now we know the formula for this, the unit for this, which is one J divided by one second. So one watt, that's the unit of power watt is equal to one J per second and the abbreviation is W. Well, it's a little bit confusing maybe. This is not abbreviation of the unit. Abbreviation of unit is J. W is just because of the word work which we're using and P because the word is power. So these are concepts and these J and W are units. J for J for work and W for watt for power. So this W should not be mixed with this W. This is unit. This is a concept. This is a watt. This is work. So obviously there are many different tables, how different units are related to each other. For example, power can be measured, let's say it's horsepower or something like this. I'm not going to do any kind of conversion right now. If you want, you can go to internet and find out what it is. I'm talking only about the units in C, in the system, which has been established as the standard in physics and in many other places, like technology, in industries, whatever. Okay, so that's the power. That's another new concept. All right, and now let's go back to energy. Now as we see, whatever I have defined here is related to movement, mechanical movement, force times distance, object has certain mass, etc., acceleration because of the force. Now these are all mechanical issues. Energy is much more kind of a general concept. So the energy in all these cases basically is capacity to perform work. So when we are saying that certain force or certain source of energy, if we can say so, performed such and such work, let's say it moves objects from A to B and it spends certain amount of work according to the formula, whatever we calculate the work. We are saying that this particular source of energy spent, that amount of energy, which is equal to amount of work. So in these cases, we can actually say that, okay, energy is basically capacity to perform work. And whenever something or somebody actually does the work, performs the work, it spends energy exactly equal to amount of work, which has been performed. So energy basically is a concept which also measured in Joe's J. Now what about chemical energy? I mean when we were talking about energy, and there is a whole part of the course dedicated to energy, chemical energy, nuclear energy, whatever, what else here, electromagnetic energy, gravity as an energy, gravitational field. I mean there are many different types of energies, but if you think about these other things related to energy in a more, in a deeper way, you will actually see that there is some movement everywhere. For instance, if we are talking about chemical energy, chemical energy related to movements of ions between certain, I don't know, two liquids or whatever, they're exchanging electrons, they're exchanging certain composition of molecules, there is always some kind of a movement. And energy really is always related to movement of something. Nuclear energy is related basically to like splitting the nucleus, and that's also some kind of energy being released because something was inside, and now we are just releasing it outside. There is always a movement of something. So it's no wonder that any energy, in any kind of incarnation, we measure in Jaws, in the system C. So basically all we can say right now that energy always manifests itself in work it can perform. We might not even know how much energy is concentrated somewhere until that energy is being released and it makes it, it does some kind of a work. So that's why we can predict certain things. I mean we can calculate how much energy might be released and perform work. Remember the potential energy or kinetic energy, for instance, the moving object has certain kinetic energy. Why? Because if we will force that moving object to perform some work, for example, move another object to accelerate it, for instance the billiard ball, it's actually rolling and rolling. It does not perform any work, but it does have a potential, it does have a kinetic energy because it's moving. As soon as it hits another ball, that's the work which is being performed. And the first ball stops and the second ball starts moving further, which means the energy has been transformed from one to another. But it's always work. Now in this case the rolling ball, the first ball having certain energy in its movement does the work of hitting and accelerating the second ball. So energy is basically a capacity to perform work. It can be related to movement, which is kind of a mechanical type of energy, which is kinetic energy. Or it can have a potential energy like, for example, the field, gravitational field. It has a potential energy because if I have something like a stone, for example, I keep it in my hand, nobody performs any work, but as soon as I let it go, gravitational energy performs work to accelerate it when it goes down. So we can say that whatever the work has been performed by gravitational field used to be in this stone on a certain height over the surface of the earth, it was a potential energy. So potential energy also can be measured in the work. We can predict, so to speak, how much work will be performed if we will release the stone at a certain distance over the earth. So basically that's it. My purpose was to introduce Joel and Wat, two measures, measures of energy in C. And again, granted my explanation was initially mechanical, so to speak. I'm just telling that all other kinds of energy in some way are related to motion of different components of the objects, atoms or even parts of the atoms like protons or electrons, or even inside the proton and electrons. Sometimes all these quarks or whatever else we were talking about, they are doing certain work and that's the source of energy. Okay, that's it for today. Thank you very much and good luck.