Learn about Newton's Third Law of Motion Video

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Learn about Newton's Third Law of Motion

Now we’re ready for Newton 3rd law and Newton’s 3rd law in some ways I think is the most fun because its—at least it was to me the list intuitive apart all the laws. But once you really kind of understand it a lot of things start to make sense. So the Newton’s 3d law essentially says but actually I can tell you kind of what you might have heard, you know, a lot of people say every action has an equal and opposite reaction. Another way of thinking about it is if there's an object and it excerpt of force in another object so let say I have a—let me think of something. Let say that I have a fist and it is punching someone faces so this is the face and they're not happy. Right, and let say this fist is punching the face with the force of 10 Newton’s. Let's not make it so violent. Let say that, this is a hand massaging the face it pressing upon the face with the force of ten Newton’s. So what Newton’s 3rd law tells us is that the face is also I guess we could say punching the hand or no, we’re not we’re not using the violent. The face is also pressing upon the hand with the force of 10 Newton’s in the opposite direction put along the same I guess you could say along the same line. So does that make any sense because it seems like the hand is doing something to the face and not the other way around. But if you think about it when you press on someone’ face their face might kind of pressing a little bit but you also feel something on your fist or on your hand. I mean think of it maybe a better example would be instead of someone’s face imagine if it was a tree that you’ve decided to massage or I guess punch. So here is the tree and the same thing would happen, if you were to press upon the tree with—if you were to punch the tree essentially the tree is essentially punching back with the exact same force. And here it makes sense because your hand will hurt and maybe in this case the face will hurt because the face kind of gives way while your fist doesn’t. But here the tree is not giving way and your fist will. Another way to think about it is if and this is probably the list intuitive if I have the earth and here am I standing on top of the earth. So we already figure out that the pull of the earth of the force of gravity upon me its pulling down upon me at 150 pounds that’s the force. And you know we could say the pound is a unit of force, its weight. But it also Newton’s 3rd law tells us that I'm actually at the same moment pulling on the earth with the force of 150 pounds. And I know this might not make a lot of sense to you but you can think about it this way. When I stepping on, let say I'm stepping on a soft surface like sand or something I feel my feet were compress a little bit but so does the sand probably by, you know, well depending on which one softer. And another way to think about it also is if me in the earth are both in deep space and I am, you could say falling towards the earth because the earth is pulling on me. How do we know that earth isn’t falling towards me? I mean it’s kind of arbitrary there's no frame of reference we’re both in deep space there's nothing else to look at. We’re essentially falling towards to each other. I'm not necessarily falling to the earth the earth not necessary falling to me we’re just falling towards each other. And that’s another way of thinking about thinking about this. So you could think about every example where force supplies to something and if you really think about it the force is going the other way as well. For example if I were to take a bat to this tree and swing on it really hard so I would have swing on this tree really hard I have a good chance of breaking that bat even though you would have thought, “Hey, that bat is applying the force to the tree but why is the bat breaking?” Because the tree is applying an equal force to the bat and actually if I did it perfectly if I had like—let say I had two bats or two swords for some reason I think I'm going a little too mile to the example but I guess you know we’re talking about forces so maybe violence is justify here. Well, let say I have two swords that are completely identical hitting each other, right. And at some point and let say I keep increasing the force at which they're kind of going in opposite directions. At some point they're going to break, right. If I just keep increasing the force on one guy swinging in one direction, one guy swinging in the exact opposite direction and the force is keeps increasing at some point they're going to break And you could say that—well, this guy says, “Well, I was the only guy swinging because this guy was stationary” and the other guy says, “Well, I was the only guy swinging because this is guys was stationary.” But some points not one of them was going to be break they're both going to break because even though this mow sword was pushing on this blue sword with some force the blue sword was essentially pushing that with the exact same force. So these are completely identical swords at some point they're going to break. Another way we can think about it one of the swords could have just been held stationary, it could have been held stationary by somebody and there's other sword that if you were to press down then kept increasing the force with what you press at some point they both would break because one there identical. If one was hard on the other then that would stick around. Hopefully that’s gives you a little intuition, I mean we could do a bunch of more examples I'm trying to think. Oh, let me think of another one. Let say we’re in deep space again and I have a basketball and it weighs one kilogram. And let say that I weigh 50 kilograms. So let say I push my hand pushes on this ball with the force of, I don’t know let say I push on that ball with the force of 10 Newton’s to the right. What Newton’s 3rd law tells me is that essentially that basketball is going to push on my hand with an equal and opposite force that’s going to push on me with the force of ten Newton’s. So what's going to happen? So we’re touching I'm pushing on ten Newton’s on the basketball we’re in deep space there's no gravity for random stars et cetera, et cetera. And then the basketball going to push on me with the force of 10 Newton’s simultaneously. So the basketball we know that f = ma, so the basketball so 10 Newton’s is equal to one kilogram times accelerations. So acceleration is going to be 10 meters per second squared to the right so as long as we’re touching the basketball it's going to accelerate at 10 meters per second squared to the right. And simultaneously I'm going to accelerate at certain acceleration to the left and what's that going to be? So we know that the force to the left is going to be 10 Newton’s and that equals 50 kilograms times’ acceleration. So here the acceleration is going to be 1/5 meters per second squared. So when I push on—so we’re both in deep space floating around and I push on this one kilogram basketball with the force of 10 Newton’s as long as I'm pushing on it it’s going to accelerate at 10 meters per second squared as long as I'm pushing it. But simultaneously when I'm pushing on it, it exerting an equal and opposite force of me on 10 Newton’s so I'm going to actually move back a little bit at the slower acceleration and that’s just because I have more mass at 1/5 meters per seconds squared. Another example you can think of is if someone shoot s a gun, right. There's that I forgo the term because I don’t shoot guns but you know that you're shoulder jerks back as I've seen in the movies when the bullet shut. And that because the gun is exerting a force on that bullet and the bullet is exerting an equal and opposite force on the gun and which kind of pushes back on your shoulder, and the reason why the bullet just goes a lot, lot faster forward than you and the gun go backward is because your mass is much, much, much larger than the bullet. Hopefully that gives you a little bit intuition on Newton’s 3rd law. And this is kind of none intuitive so look around you in the world and look at all the forces that are being applied and I want you to think about, you know when one force is being applied in one direction why does it make sense that another force an equal and opposite force is being applied in the exact opposite direction. I'll see you all in the next video.

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Now we’re ready for Newton 3rd law and Newton’s 3rd law in some ways I think is the most fun because its—at least it was to me the list intuitive apart all the laws. But once you really kind of understand it a lot of things start to make sense. So the Newton’s 3d law essentially says but actually I can tell you kind of what you might have heard, you know, a lot of people say every action has an equal and opposite reaction.

Another way of thinking about it is if there's an object and it excerpt of force in another object so let say I have a—let me think of something. Let say that I have a fist and it is punching someone faces so this is the face and they're not happy. Right, and let say this fist is punching the face with the force of 10 Newton’s. Let's not make it so violent. Let say that, this is a hand massaging the face it pressing upon the face with the force of ten Newton’s. So what Newton’s 3rd law tells us is that the face is also I guess we could say punching the hand or no, we’re not we’re not using the violent. The face is also pressing upon the hand with the force of 10 Newton’s in the opposite direction put along the same I guess you could say along the same line. So does that make any sense because it seems like the hand is doing something to the face and not the other way around. But if you think about it when you press on someone’ face their face might kind of pressing a little bit but you also feel something on your fist or on your hand. I mean think of it maybe a better example would be instead of someone’s face imagine if it was a tree that you’ve decided to massage or I guess punch.

So here is the tree and the same thing would happen, if you were to press upon the tree with—if you were to punch the tree essentially the tree is essentially punching back with the exact same force. And here it makes sense because your hand will hurt and maybe in this case the face will hurt because the face kind of gives way while your fist doesn’t. But here the tree is not giving way and your fist will.

Another way to think about it is if and this is probably the list intuitive if I have the earth and here am I standing on top of the earth. So we already figure out that the pull of the earth of the force of gravity upon me its pulling down upon me at 150 pounds that’s the force. And you know we could say the pound is a unit of force, its weight. But it also Newton’s 3rd law tells us that I'm actually at the same moment pulling on the earth with the force of 150 pounds. And I know this might not make a lot of sense to you but you can think about it this way. When I stepping on, let say I'm stepping on a soft surface like sand or something I feel my feet were compress a little bit but so does the sand probably by, you know, well depending on which one softer.

And another way to think about it also is if me in the earth are both in deep space and I am, you could say falling towards the earth because the earth is pulling on me. How do we know that earth isn’t falling towards me? I mean it’s kind of arbitrary there's no frame of reference we’re both in deep space there's nothing else to look at. We’re essentially falling towards to each other. I'm not necessarily falling to the earth the earth not necessary falling to me we’re just falling towards each other. And that’s another way of thinking about thinking about this.

So you could think about every example where force supplies to something and if you really think about it the force is going the other way as well. For example if I were to take a bat to this tree and swing on it really hard so I would have swing on this tree really hard I have a good chance of breaking that bat even though you would have thought, “Hey, that bat is applying the force to the tree but why is the bat breaking?” Because the tree is applying an equal force to the bat and actually if I did it perfectly if I had like—let say I had two bats or two swords for some reason I think I'm going a little too mile to the example but I guess you know we’re talking about forces so maybe violence is justify here.

Well, let say I have two swords that are completely identical hitting each other, right. And at some point and let say I keep increasing the force at which they're kind of going in opposite directions. At some point they're going to break, right. If I just keep increasing the force on one guy swinging in one direction, one guy swinging in the exact opposite direction and the force is keeps increasing at some point they're going to break

And you could say that—well, this guy says, “Well, I was the only guy swinging because this guy was stationary” and the other guy says, “Well, I was the only guy swinging because this is guys was stationary.” But some points not one of them was going to be break they're both going to break because even though this mow sword was pushing on this blue sword with some force the blue sword was essentially pushing that with the exact same force. So these are completely identical swords at some point they're going to break.

Another way we can think about it one of the swords could have just been held stationary, it could have been held stationary by somebody and there's other sword that if you were to press down then kept increasing the force with what you press at some point they both would break because one there identical. If one was hard on the other then that would stick around.

Hopefully that’s gives you a little intuition, I mean we could do a bunch of more examples I'm trying to think. Oh, let me think of another one. Let say we’re in deep space again and I have a basketball and it weighs one kilogram. And let say that I weigh 50 kilograms. So let say I push my hand pushes on this ball with the force of, I don’t know let say I push on that ball with the force of 10 Newton’s to the right. What Newton’s 3rd law tells me is that essentially that basketball is going to push on my hand with an equal and opposite force that’s going to push on me with the force of ten Newton’s.

So what's going to happen? So we’re touching I'm pushing on ten Newton’s on the basketball we’re in deep space there's no gravity for random stars et cetera, et cetera. And then the basketball going to push on me with the force of 10 Newton’s simultaneously. So the basketball we know that f = ma, so the basketball so 10 Newton’s is equal to one kilogram times accelerations. So acceleration is going to be 10 meters per second squared to the right so as long as we’re touching the basketball it's going to accelerate at 10 meters per second squared to the right. And simultaneously I'm going to accelerate at certain acceleration to the left and what's that going to be?

So we know that the force to the left is going to be 10 Newton’s and that equals 50 kilograms times’ acceleration. So here the acceleration is going to be 1/5 meters per second squared. So when I push on—so we’re both in deep space floating around and I push on this one kilogram basketball with the force of 10 Newton’s as long as I'm pushing on it it’s going to accelerate at 10 meters per second squared as long as I'm pushing it. But simultaneously when I'm pushing on it, it exerting an equal and opposite force of me on 10 Newton’s so I'm going to actually move back a little bit at the slower acceleration and that’s just because I have more mass at 1/5 meters per seconds squared.

Another example you can think of is if someone shoot s a gun, right. There's that I forgo the term because I don’t shoot guns but you know that you're shoulder jerks back as I've seen in the movies when the bullet shut. And that because the gun is exerting a force on that bullet and the bullet is exerting an equal and opposite force on the gun and which kind of pushes back on your shoulder, and the reason why the bullet just goes a lot, lot faster forward than you and the gun go backward is because your mass is much, much, much larger than the bullet.

Hopefully that gives you a little bit intuition on Newton’s 3rd law. And this is kind of none intuitive so look around you in the world and look at all the forces that are being applied and I want you to think about, you know when one force is being applied in one direction why does it make sense that another force an equal and opposite force is being applied in the exact opposite direction.

I'll see you all in the next video.

Transcription by: Scribe4you Transcription Services