Now, nice to meet you. Dear students of Jongjung School . Okay, the science exam is next week, and since it seems like you guys are finding the material a bit difficult, I prepared this video to review it for you before the test . Now, first of all, the most important thing covered in this exam is power. Strength. But this strength is really difficult. No one will find it easy . Nevertheless, the reason we need to learn this is because it is extremely important. Because I said that power is the very beginning of science . Oh, Newton. So, just as we started science in middle school, we need to understand force to easily understand the rest of the subject, which is why we began learning about force as soon as we entered middle school . However, it is really not easy. The reason it is difficult is primarily because we use terms like "strength" and "oh my" indiscriminately in everyday life. How do we use them in our daily lives ? I'm talking about power. it's hard. It gives me strength. I have no strength. We use all sorts of expressions related to force in everyday life, like saying "cheer up" and all sorts of other things; this is actually the definition of force that Newton established . Force is a word coined by Newton. In fact, the statement that something was made is a clearly defined concept. Newton didn't make it so that we would just use it haphazardly; he clearly defined what it meant, but despite that, we use it carelessly and indiscriminately in our daily lives. And generally speaking, these terms are completely different from the concept defined by Newton. So, when science books say, "This is what force is," the majority of us misunderstand it in a very strange way . That is why, unless this wrong power in your head—that power—disappears from your minds, you must have had a really bad headache studying power during this exam period . Now, secondly, the reason strength is difficult is that the concept is n't familiar. Now, this concept of force defined by Newton is completely different from the concept we use in everyday life, and you probably have never thought about it before. That is why, uh, since it’s not familiar, it will be difficult to accept. Now, and lastly, the reason the strength is difficult is that there is a lack of time. Now, is it really easy to understand this concept—which is so important it could be called the beginning of science—when it has been about a month and two weeks since we started school ? It definitely won't be . I'm very short on time. Nevertheless, the reason we must learn this power first is that it is that important. And despite the many reasons why it is so difficult, I believe that if I make this video to help you, you will be able to understand it well . So, first of all, the word 'power' is written in the textbook as follows: power. It is defined as " force" as the cause that changes the shape or state of motion of an object. If you just look at what he said, you might think it’s nothing special, but the part you really need to pay attention to is "changing the state of exercise ." It is important to properly understand this phrase . Saying that the exercise has changed and saying that the location has changed are completely different things . Now, saying that motion has changed means, for example, that I am moving at a speed of 30 m/s . The act of doing some kind of exercise. If, after some time has passed, I am still exercising at a speed of 30 m/s, has this person's exercise changed? It hasn't changed. Because the speed is still being maintained at 30 m/s . So, has your exercise changed or not ? It hasn't changed. In other words, according to the definition of force, force is the cause that changes the state of motion. My exercise status hasn't changed. So, in this case, is there power or not? This person currently lacks real power . The net power is 0 . Has the location changed? It has changed. why? Since the speed is 30 m/s, it is moving 30 m per second. But this has nothing to do with power . But what do we think? Our wrong thinking. You need strength to move . The more I move, the more I lose strength. Because they are having all sorts of really wrong thoughts like this, oh, they have power. Then I should move. It stops. I have no strength. Or maybe it's moving . Looks like someone is pushing them. Or it seems like it has power. I think like this, but all of this is just absurd thinking. That is all wrong thinking, and you need to remove all the concepts of power that you had in your heads before we learned about science—what is this power now? I just have nothing in my head. You need to hear the explanation after you reach this state . The reason you are struggling is because you have the wrong mindset right now. hmm. It might sound a bit like a cult, but please believe me. 99%, no, 100% of the power you think you know is all wrong. Now, why did you say Newton made it? Uh, if it's not the force Newton talked about, you can just consider everything else wrong . Okay, let's go back to the beginning. What is power? Uh, force is the thing that changes the state of motion, that is, speed. Let's just talk comfortably like this. Having power means that the speed has changed . okay? Or, the point is that as long as it changes, regardless of which of the two directions it takes, there is power . Now, one of the things you all misunderstand the most. I think that the first moving object must have force. Now, the reason I'm thinking of this kind of entertainment is... well, let's take a look at a simulation first . Now, I will push the object . Now, if you push, ah, again, oh, it will push the object . What happens if you give it a push ? What is the speed like? As you can see in the top left, this is the speed dog. The speed is getting faster and faster. Now, this is what power is. If you have power, the speed increases. Now, see what happens if I take away my power here . I will remove the power. Then, shall we stop here? no. It doesn't stop. It's just that what changes? Movement disappears during speed reading. The speed stopped. It means the change in speed stopped. You can move even without strength. It just means that the exercise isn't changing because there is no strength . The fact that the speed doesn't change . Now, if you apply force again, the speed changes. Having power means that the movement changes, and the best example of movement changing is that the speed is increasing . Take your hand off again. The speed doesn't change. Think again. Does a moving object need to have force? no. Moving has nothing to do with strength . Force makes things move faster or slower, or even changes direction—it changes things like speed and velocity . Uh, if you move, you have power. no. Now, they have the illusion that they can transmit the second power. For example, if I kick the ball, I have transferred power to the ball . The ball has power, so call it. The ball will lose strength as it rolls and stop. There are so many people who think this way, but there is n't a single proper statement here. That's all wrong . Now, power is n't something you transmit. transmission. And the ball, and the ball doesn't roll because it has power . It doesn't lose strength as it rolls . Now, power is not a concept that can be conveyed. Generally, when they are in contact, it is the cause that changes the object's speed, and the moment they are not in contact, the force disappears. What it means to have no power is that there is no change in speed . Okay, let's look at the simulation one more time . Now, the object is stationary, right? This is the speed. The speed is zero. If you want to change the speed, you just need to apply force to it . How do you apply force? I just need to touch it . Push against it. Now, what happened to the speed when force was applied ? It gets faster. But what happened to your strength when you let go? It's gone, right? It is powerful. I have no strength. It is powerful. I have no strength. It is powerful. does not exist. It has power only when your hands are fully engaged; when your hands are fully engaged and pushing, the speed increases, and the moment you let go, the power disappears and the speed no longer changes. This is how you need to understand it. okay. First of all, there are exceptions. There are exceptions, such as gravity, electricity, or magnets, which can apply force without direct contact. However, generally speaking, for the topics we will be covering at our level— excluding gravity—you can assume that force exists only when there is contact . And just because an object isn't in contact or lacks force doesn't mean it stops. You just need to understand that the speed does not change . But the reason this is difficult to understand is, teacher, for example, when I move objects—for instance, when I'm dragging or pushing a heavy box—if I think about it, it only moves when I apply force, and stops if I don't. The thought that Because of this experience, I have come to think that I should only move when I have strength, and stop when I do not. But you guys missed one thing. Well, you are forgetting the existence of friction . Now, what I mean is that we have to push it like this to make it move. And what happens if I don't push ? Stop. Okay , right now I can't see anything. Again, ah, I see. It only moves if I push it, and stops if I don't. Ah, it is not that an object stops only when I apply force, and stops unconditionally if there is no force . What I mean is, it's because you are n't thinking about the fact that there is friction right now . Now, the reason I can move this is that something that was stationary moved. The exercise has changed. Because I had the strength. And the reason it stops is not because it lacks power, but because the friction on the floor slows it down. It stops because it has the power . I'm going to push him again. Push, push. So, net power has been generated, and since there is power, what happens? The object starts to move. But since there is a net force, what is the speed? It's gradually increasing. But here, I'll relax . So, what happened to the speed? It's consistent, right? why? If I gradually reduce my force and push with a force equal in magnitude to the friction, the net force becomes zero. So, even though I'm pushing, what is the speed? It's consistent. why? Since it counterbalances with friction and the net is 0. okay. Just because I say I give strength doesn't necessarily mean there is some real, substantial power . This concept is also wrong right now . So, the reason it stops when I let go is not because the force I applied is lost, but because the pushing force disappears and the only force hindering it is friction, which causes a change in speed. Changes in exercise . So what happens ? It gradually stops. So, the moment I don't make contact— what I mean is, I have to exert force for it to move. It only appears that way because there is friction that causes it to stop if you don't apply force . What if there were no friction ? It will get faster if I put more force into it, right? Gradually. Then, don't apply force. It's not that he's going to stop. It’s not that it will stop because I’m not pushing it; it’s that there is no reason for it to stop right now because there is no friction . Why do we stop in everyday life ? It stopped because of friction, not because the force I applied ran out . Now, anyway, one of the things you keep misunderstanding is that, lastly, I keep talking about the force of an object . When an object stops, stopping means the object loses its force. Or, people think that the reason an object moves is because the object has force, or that the object possesses some kind of force . The problem is that there is no concept of power as belonging to someone else, being mine, the teacher's power, your power, or one's own power . You keep thinking that way, but regarding power, please remember this well. Power can only be expressed in this way, unconditionally, to B. Force must always be expressed as who exerts force upon whom. Uh, well, I don't have any heretical powers or anything like that . I’ll try to express the power of the heretical type—or rather, the power of the box—in a very strange and wrong way . I am pushing a box. I'll express this in a strange way, in your own style. The heretic borrowed the box, and the heretic's power was transferred to the box. The box gains power and moves. The box keeps losing strength. Just like we lose strength if we don't eat, what do you mean if Lee Dan doesn't keep pushing us? If you don't keep supplying force, the box will lose power and stop. That statement itself is completely nonsensical . The point is that you shouldn't understand it like this . If you are thinking here, "Oh, that sounds right," then you have already misunderstood. What should I say? Then, the situation where the box is being pushed. How should we talk about power? Someone always acts on or influences someone else . You have to say it like this. Okay, the situation is that a box is being pushed . Who is the heretic, to whom? Give strength to the box. As a force is applied, the speed changes, so the box gets faster and faster. The box fits not only the single type but also the bottom . The floor applies friction to the box. To whom? To the box. Friction hinders the movement of the box because it is opposite to the direction of motion. okay. If the pushing force of the heretic is greater than the pushing force of the heretic who trusts whom, the box will speed up. At that time, if the heretic takes his hand off the box, the force the heretic exerts on the box disappears. It means there isn't one . Now, the only force applied to the box is the frictional force exerted by the floor on the box . The box slows down due to friction . Eventually, the box will stop . You need to be able to say it like this . There is not a single wrong word in this . Power is not something that can be transmitted. It means that getting that isn't hiding my identity . okay? It is applied only when the hand connects, and that is all that changes the speed . Now, since I gave this explanation with a positive attitude without being fully prepared, it might be a bit unclear. However, if you don't understand, let's at least try to properly understand what " strength, strength, strength" actually is, even if it means repeating it . If there is something in the content that you don't understand right now, it will continue to be difficult. I hope you understand the power, even if it requires repeating it many times.