Well, nice to meet you. Dear students of Jongjung Middle School . Okay, next week is the science test, and I think you guys are having a little trouble with the science material before the test, so I prepared a video to summarize it . Okay, first of all, the most important thing we're going to cover in this exam is strength. Power. But this power is really difficult. No one will have it easy . Nevertheless, the reason why we must learn this is because it is so, so important. Because this is what I said: power is the beginning of science . Oh, Newton. So, since we started studying science in middle school, we need to know about force to easily understand the rest, so we started learning about force as soon as we entered middle school . But it's really not easy. The reason it is difficult is because the first power is that we use the term indiscriminately in our daily lives. How do we use it in our daily lives ? It's called strength. it's hard. It's hard. I'm weak. We use words like "Cheer up" and "All kinds of force-related words" in our daily lives, but Newton defined the word force . Force is a word coined by Newton. In fact, the word "created" is a clearly defined concept. It's not that Newton created it to be used roughly, but he clearly defined what force means, and yet we still use it roughly and haphazardly in our daily lives. And by and large, these words are completely different from the concepts defined by Newton. So when we read in science books that this is what power is, we often get a very strange and misunderstood impression. That's why, unless this wrong power, this power, doesn't disappear from your head, oh, you must have had a lot of headaches studying power during this exam period . Now, the second reason why strength is difficult is because the concept is unfamiliar. Now, this concept of force defined by Newton is so different from the concept we use in our daily lives that we probably have never thought about it. So, uh, because you're not used to it, it's going to be hard to accept. Okay, and finally, the reason strength is difficult is because there is not enough time . Now, is it really easy to understand this concept, which is so important that it can be called the beginning of science, after only a month and two weeks of school ? Absolutely not . I'm really short on time . Nevertheless, the reason why we must learn this power first now is because it is that important. And even though there are many reasons why it's so difficult, I believe that if I make this video to help you understand it better, Okay, so first of all, how is the word power written in the textbook? It's power. Force is the cause that changes the shape or state of motion of an object. If you just look at his words, you might think, "Oh, it doesn't seem like much," but what you really need to pay attention to is how he changes his exercise state . It's important to understand this properly. It's a world of difference that the movement has changed and the location has changed . Now, when we say that the motion has changed, we could say, for example, that I am moving at a speed of 30 m/s . What kind of exercise do you do? If after some time I am still moving at a speed of 30 m/s, has this person's movement changed? It hasn't changed. Because the speed is still 30m/s and the motion is still continuing . So, has exercise changed or not ? It hasn't changed. That is, according to the definition of force, force is the cause that changes the state of motion. The exercise status hasn't changed. Here, then, there is power, or there isn't. This person has no real power right now . The net power is 0 . Has the location changed? It has changed. why? Since the speed is 30 m/s, it moves 30 meters per second. But this has nothing to do with strength . But what do we think? Our wrong thinking. Well, you need strength to move . The more I move, the more strength I lose. It's so powerful because I'm just randomly thinking about these really wrong things . Then we have to move. It's stopping. I have no strength. Or it's moving, it's moving . I wonder who's pushing me. Or maybe you have the power. I'm thinking this way, but all of this is completely out of the blue. It's all wrong thinking, and we need to take out all the concepts of power that we had before we learned science, what is science now, this power. I just have nothing on my mind. I need to hear an explanation after I get to this state . The reason you guys are having a hard time right now is because you have wrong ideas. hmm. It may sound a bit cultish, but trust me. 99%, no, 100% of what you think you know is wrong. Now, why did Newton make it? Well, if it's not the force that Newton talked about, then you can just assume it's all wrong. So, back to the beginning, what is strength? Well, force is something that changes the state of motion, that is, speed. Let's just talk comfortably like this. What it means to have power is that this speed has changed . okay? Or, if something changes, whether it's in one direction or the other, then there's power . Now, one of the things that most of you misunderstand. The first thing that comes to mind is that a moving object must have a force. Okay , so the reason I'm thinking about this kind of hospitality is , let's first take a look at a simulation . Okay, I'm going to push the object . Okay, so how about the noodle, ah, again, it's going to push the object . What happens if you push it? How is the speed going? As you can see in the upper left, this is a speedometer. The speed is getting faster and faster. Well, this is what power is. If you have strength, your speed increases. Now, let's see what happens if I take away the power here . I will take away your power. So should we stop here? no. It doesn't stop. Just what changes? There is no movement in the reading. The speed has stopped, the change in speed has stopped. You can move even if you don't have strength. Just because you do n't have the strength doesn't mean your movement doesn't change . That the speed doesn't change . Now, if you apply force again, the speed will change. Having power means that the motion is changing, and the best example of a motion changing is that it is getting faster . Take your hands off again. The speed doesn't change. Think again. Does a moving object have to have a force? no. Movement has nothing to do with strength . Force is something that changes speed, velocity, or anything else, whether it's making something move faster or slower, or changing direction . Oh, if you move, you have power. no. Well, the second power is the illusion that it can be transmitted. For example, when I kick a ball, I transfer power to the ball . The ball is powerful, so call it. As the ball rolls, it loses its strength and stops. There are a lot of people who think this way, but there is nothing right to say about it. They are all wrong . Now, power is n't something that's transmitted. transmission. And the ball, and the ball doesn't roll because it has power . It doesn't lose any strength as it rolls . Now, power is not a concept that can be communicated. Generally, when there is contact, the force causes the object's speed to change, and the moment there is no contact, the force disappears. What I mean by no power is that there is no change in speed . Okay, let's look at the simulation again . Okay, so the object is stationary? This is speed. The speed is amazing. If you want to change the speed, you can apply force to it . How do you apply force? I can put my hands on it. Push hard. Now, what happens to the speed when force is applied ? It gets faster. But what happened to the strength when I took my hand off? It's gone, right? It's powerful. I have no strength. It's powerful. I have no strength. It's powerful. does not exist. It's only powerful when you have all your hands, and when you have all your hands and you're pushing and you have power, the speed increases, and the moment you take your hands off, there's no power and the speed doesn't change anymore. This is how you should understand it. okay. First of all, there are exceptions. There are some things that can exert force even when they are not in direct contact, such as gravity, electricity, magnets, etc., but in general, most of what we will deal with at our level, excluding gravity, can be thought of as a force that exists only when there is a force . And just because there is no contact or no force doesn't mean the object stops. You just have to understand that the speed doesn't change . But the reason why this is difficult to understand is because, teacher, when I move something, for example, when I drag a heavy box or push something, if I think about it, it moves only when I apply force, and if I do n't apply force, it stops. The idea that. This experience makes me think that I need to have strength to move, and if I don't have strength, I should stop. But you guys are missing one thing. You're forgetting the existence of friction . So what I mean is, we have to push like this to get it to move. And what happens if I don't push ? Stop. Okay , I can't see anything right now. Again I know , I have to push it to move and if I don't push it stops. Ah, so an object is something that I have to apply force to stop it, and if I don't apply force, it stops unconditionally. That's not it . What I mean is, you're not thinking about the friction right now . Now, the reason I can move this thing is because it was still and now it's moving. Exercise has changed. Because I had the power. And the reason it stops is not because it lacks strength, but because the friction on the floor slows it down. It stops because it has the power . I'll push him again. Push push. Okay , so now that you have the power and the strength, what happens? The object begins to move. But since there is a net force, what happens to the speed? It's increasing more and more. But here I take my strength away. So, how's the speed? Is it regular? why? If I gradually release my strength and push with a force equal to the frictional force, the net force becomes bread. So what happens to the speed even though I'm pushing? It's regular. why? Because it is a net 0 when compared to frictional force . okay. Just because I say I give you strength doesn't mean there's some real strength . This concept is also wrong now . So the reason it stops when I let go is not because the force I gave it is gone, but because the force I was pushing is gone and the only force that is holding it back is friction, which causes a change in speed. Changes in movement . So what happens ? It's gradually coming to a halt. Okay, so the moment I don't touch it, what I mean is, I have to apply force for it to move. It only appears that way because there is friction that stops it if you don't apply force . What if there was no friction ? If I give it some strength, it will go faster, right? More and more. Then don't give it any strength. Then he said he won't stop. It's not that I'm not pushing hard enough to stop, it's that there's no friction right now, so there's no reason to stop. Why does it stop in everyday life ? It stopped because of friction, not because I lost all the strength I gave it . Okay, so anyway, one of the things that you guys keep misunderstanding is, I keep talking about the last thing about an object is the force of the object . When an object stops, the force that causes it to stop is released. Or, we think that the reason an object moves is because the object has force, or that the object has some kind of force . The problem with this is that there is no concept of power as someone else's, mine, the teacher's power, your power, or your own power . I keep thinking that way, but remember what strength is. Power can only be expressed unconditionally like this, from A to B. Power must always be expressed in terms of who exerts it on whom. Oh, there's no such thing as heretical power . I'll try to express it in a very strangely wrong way, like the power of a two-part box . I'm in a situation where I'm pushing a box. Let me put this in a weird way for you guys. The heretic borrowed the box, and the heretic's power was transferred to the box. The box gains power and moves. The box continues to lose strength. Just like we lose strength if we don't eat, what does it mean if Idanhyung doesn't keep pushing us? If you don't keep transmitting power, the box will lose power and stop. This statement itself is completely nonsensical . You shouldn't understand it like this . If you're thinking, "Oh, that sounds right," then you've already misunderstood. What should I say? Then, the situation where the box is being pushed. How should we talk about power? There is always someone doing or acting on someone . I have to say this. Okay , here's the situation where you're pushing a box . Who is the heretic? Who is the heretic? Gives strength to the box. As force is applied, the box's speed changes, so it gets faster and faster. The box fits not only the top but also the bottom . The floor exerts frictional force on the box . To whom? To the box. Friction opposes the motion of the box because it is opposite to the direction of motion. okay. If the force exerted by the heretic is greater than the force exerted by the heretic, the box will speed up. When the heretic releases his hand from the box, the force the heretic exerts on the box disappears. That means there isn't one. Now the only force acting on 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 have to be able to talk like this . There is nothing wrong with this . Power is not something that can be transmitted. That's what I got and it's not Ilko . okay? It's only applied when the hand is right, and that's what changes the speed . Okay, I'm not quite ready to explain this, so it might be a little unclear, but if you don't understand, let's try to understand what power, power, power is, even if it means repeating it. If you don't understand something in this content, it will continue to be difficult. Please understand the power even if it takes several repetitions.