 All right, guys, so I can see that attendance is little less. I was expecting full attendance today because I have to start this particular chapter since it has been getting delayed. Bharath, whatever frame you take, answer will not change. Time is independent of your frame, unless you are moving with speed of light or something. Anyways, so what I'm trying to say here is that maybe your exams are on or whatever pressures you may have, but then try attending all the classes, all right? Every class is very, very important. We discuss things which are beyond your, you know, at times, whatever is discussed in the school also. So these classes are very important. Anyway, since this is an online session, it will get recorded and available to you. But my point is, do not miss any of the classes. Anyways, write down this chapter name, which we are going to start. I hope you have enjoyed Laws of Motion Chapter and you can appreciate how simple the theory is and how difficult or how tricky the questions can be, OK? So it's fun, you know, to try out various types of questions in Laws of Motion Chapter and it's a constant learning process. Do not try to master each and everything of Laws of Motion in just couple of weeks or couple of months. You just have to solve like 100 to 200 questions and move forward. Slowly and slowly, you will master Laws of Motion Chapter. It takes a year or one and a half years to master that. So but then you can't stop and just do that chapter, OK? Write down work, power, energy, or work, energy, power. So the name of the chapter is not a phrase. It's just like three things which you are going to learn in this chapter. Work you will be learning. What is work? Physically, how you will quantify it. Then you will be learning what is power and then you will be learning what is energy, OK? So you will not stop after learning it individually. You'll also learn what is the connection between energy and work or what is the connection between power or work, fine? So this chapter is all about these three things which you can see as a title, fine? Work, power, and energy, OK? The best part of this chapter is you're not dealing with vectors, OK? Work is a scalar quantity. Power is, again, a scalar quantity. And energy is also a scalar quantity. So you never have to bother to take components of work to know the direction of the work or to know the component of energy or direction of energy. You know, you are dealing with a number, OK? Which has no direction sense. It's like a mass or time or volume density, fine? Similarly, these three terms, work, power, and energy, all right? So but then the definition of work may involve few vectors. How it is defined. The outcome is a scalar, fine? So although the work is a scalar quantity, but in order to find the work, you are dealing with vectors. So I will quickly revise few things that are useful to find the work, OK? Or the way you define the work, all right? Now, before I even go on to define all these things, I will first touch upon what it is, OK? Now, just write down these three things on your notebook. Work, power, and energy, fine? Right now we are just trying to define what it is that we are going to study. What is work? How you will define the power and how you will define the energy? Because the way you define will tell you how you will measure it, OK? Now, can you type in what do we mean by work? What comes in your mind when somebody says work is done or I'm done with the work? What does it mean, actually? Work is spending of energy, OK? See, Bharat, I'm not getting into mathematical part of the work. Right now, I just want to know what it is. As in, when somebody says, have you done your work? Like, if I ask you, have you done your homework? You will not say, OK, force into displacement, right? So the definition of work should take in all the scenarios possible, the way it is defined, what it is. Some useful outcome out of effort or energy. Does it need to be a useful outcome? Does it need to be useful? I mean, if you ask me to do something, it is one thing to not to do something, but it is another way to, if you ask me to save money and I start spending it, so I'm not doing a useful work according to what you have tasked me to. Some forced done object moves through some distance. So that is fine, but see, I'm not getting into the mathematical part of it. When somebody asks you that, have you done your work, what does it mean? If you say I'm done, so what does it mean? Work is applying force to do something. When you study for your exam, what force you are applying being involved in some activity to achieve result. More or less, you guys know what you're talking about, but then somehow you're not able to put it in proper words. So let me write down here, work is some change in the status. For example, whatever state you are in, if that state changes, be it learning something, be it doing anything, if that state is changing, then there is some change that has happened and that change defines whether work is done or not. If you meant in the same state which you were in before and after, then work is not done. So work represents some change in the status quo. Are you getting it? Now the same philosophy is taken in the physics also that it should represent a change. There should be a change. Now when you talk about a change in physics, when you talk about a change in physics, it usually means a displacement. It usually means what there was a location of object. Has it changed or not? The change in the coordinates or the displacement represents the change. Sorry, represents the change. And if that change is not there or displacement of the object is not there, then no matter how much effort you are applying, work done will be zero. It is like this. When you sit in a chair to study something, no matter how long you sit in the chair, if you have not solved five questions that I have given you for homework, you have not done the homework. You can't say that I have made so much effort because that's not I'm asking you for. I'm asking you whether you have done or not done the work, whether the status quo was changed or not. So in physics, the change is represented by the displacement. Fine. This change represented by the displacement. So if you apply an effort, if you apply an effort, which in physics is force, when you apply a force and that leads to some change, if that leads to some change or that leads to some displacement, you say that work is done by the force. Work is done is not a proper statement. When you say work is done, you have to specify which force has done the work. It's like this. If you take a mass, if you take a mass like this, if I am applying force in this direction, but the object is moving in that direction, then can you notice that this displacement, whatever is this block moving, let's say this block has moved by one meter, is this one meter because of this force? Yes or no? Is this displacement because of that force? No. So this displacement is not because of this force. So that is the reason why work done by this particular force is zero. So this force do not do any work in this particular scenario. Maybe there is a force acting from down. Let's say this is F1, which is causing the displacement. So this particular force has done the work, all right? So there has to be a sense of direction also when we talk about work done by a particular force, fine? So we will take this work or definition of work in detail in little bit time. Right now, let's talk about power. So right now I'm just introducing these three terms. So I hope you are now clear with the definition of what is work. Now can you tell me what is the definition of power? What does it mean? Now power is actually rate at which, right down, rate at which work is done, fine? So you might be doing lot of work. You might be doing 100 joules of work, okay? But if that 100 joules of work takes you one year, okay? And if there is some other person that is able to do 100 joules of work in just one hour, the amount of work done is same, but rate at which you have done the work is completely different, okay? So at times rate of work is very important, all right? It's like saying that, have you heard of Birbal Kichadi? You put a utensil, you put a utensil very far away from the flame, okay? Slowly and slowly your food will cook, okay? It will take lots and lots of time, fine? And if you are putting the utensil near the flame, maybe food will get cooked fast, fine? So amount of heat required to cook the food will be same in both, but the rate at which the heat is getting inside the food is different. So rate is a very, very important aspect of everything you do, okay? You will not, I mean, you don't want to take five years to clear JEE, right? Isn't it? So that's how, I mean, that's how important the aspect of the time is. The aspect of the time is captured by the power, how fast work is done. And the amount of change or amount of work is taken care by the definition of work, all right? So this is rate of doing work, power, fine? Now what is energy? What do you mean by the energy? Anyone of you, what is energy? Energy is ability to do work, okay? Any other answer? Capacity, potential, great, great. So energy is nothing but plain and simple. It is your capacity to do work, okay? Does it mean work is done? No, it doesn't mean that work is done. It just tells you how much capacity you have to do the work, all right? For example, a particular student may have a capacity to be in top thousand ranks, okay? But that's just a capacity. If that individual do not follow the regime in a systematic manner, do not listen to his teachers what they are saying, he'll not even be clear the JEE, forget about coming in top thousand, fine? So capacity is not the measure of how much work is done. Capacity just says that you are capable of doing work, fine? Now, if you do the work, you will spend some energy, okay? If you have zero energy, if you have no energy, you will not be able to do the work because energy is required to do the work. It is a capacity to do the work. If you don't have energy, you have zero capacity to do the work, fine? So this just tells you how much is your capability to do the work, fine? So even capacity is very important to measure until and unless you know how much energy is there, you'll not be able to effectively find out how much work you can extract out of that energy, fine? All right? So we have learned in thermodynamics, right? So this energy may be the heat energy, okay? Until and unless you know that how much heat energy is absorbed, you'll never be able to find out how much work will be coming because of that absorption of energy, fine? So all these three terms are very, very important when you will learn this, you'll see that they are mixed. I mean, you can't just study energy separately. You can't just study work separately, all right? So that's what these three terms are all about, okay? You have any doubts till now? All of you, please message if you have any doubts.