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Times 70 kilograms. Let's get my handy TI-85 out to figure this out. So I get 9.8 times 70. And that gives me 686. So this is equal to 686 kilogram meters per second squared. Or this is the exact same thing as this, the same right over here. This is the definition of a Newton. | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
And that gives me 686. So this is equal to 686 kilogram meters per second squared. Or this is the exact same thing as this, the same right over here. This is the definition of a Newton. So this is a Newton, which is appropriately named for the guy that's the father of all of classical physics. So my weight on Earth, wh... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
This is the definition of a Newton. So this is a Newton, which is appropriately named for the guy that's the father of all of classical physics. So my weight on Earth, which is the same thing as the force that Earth is pulling down on me, or that the gravitational attraction between me and Earth, I should say, is 686 N... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
Now I will ask you an interesting question. So here is Earth. And I am not even a speck of a speck of a speck on Earth. But for the sake of simplicity, let's say that this is me. I'm hanging out in the Indian Ocean someplace. So that is me. And we already know that Earth is pulling down on me with a force of 686 Newton... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
But for the sake of simplicity, let's say that this is me. I'm hanging out in the Indian Ocean someplace. So that is me. And we already know that Earth is pulling down on me with a force of 686 Newtons. Now my question to you is, am I pulling on the Earth with any force? And am I pulling on the Earth with a larger or a... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
And we already know that Earth is pulling down on me with a force of 686 Newtons. Now my question to you is, am I pulling on the Earth with any force? And am I pulling on the Earth with a larger or a smaller force than it is pulling on me? And your gut, or just your knee-jerk reaction might be, well, look. Earth is so ... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
And your gut, or just your knee-jerk reaction might be, well, look. Earth is so huge. Sal is so tiny. Clearly, the Earth must be pulling with a greater force on Sal than Sal is pulling on the Earth. Unfortunately, that's not the case. So the Earth is pulling on Sal with a force of 686 Newtons. And Sal is also pulling o... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
Clearly, the Earth must be pulling with a greater force on Sal than Sal is pulling on the Earth. Unfortunately, that's not the case. So the Earth is pulling on Sal with a force of 686 Newtons. And Sal is also pulling on the Earth with a force of 686 Newtons. So Sal is also pulling on the Earth. It makes me feel very po... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
And Sal is also pulling on the Earth with a force of 686 Newtons. So Sal is also pulling on the Earth. It makes me feel very powerful with a force of 686 Newtons. But you might say, wait, that doesn't make sense, Sal. If I have a building over here, and if you were to, let's say, jump from the building, the force of gr... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
But you might say, wait, that doesn't make sense, Sal. If I have a building over here, and if you were to, let's say, jump from the building, the force of gravity is going to be acting on you. And you're going to start accelerating downwards. It doesn't seem like the Earth is accelerating up to you. Wouldn't we all not... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
It doesn't seem like the Earth is accelerating up to you. Wouldn't we all notice that every time someone were to jump off a building if the Earth started accelerating in a major way? And the way to think about that is the force is the same. And we'll touch on this in more detail in other videos. But force is equal to m... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
And we'll touch on this in more detail in other videos. But force is equal to mass times acceleration. So when we're talking about 686 Newtons in terms of the force that Earth, the gravitational attraction between myself and Earth, and this is going to be equal to 68 kilograms, then it provides a pretty good accelerati... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
So in this case, if you solve for a over here, you're going to get the 9.8 meters per second squared. Now, if you do the same thing for Earth, I already told you that we're pulling on each other with the same force, 686 Newtons. But now, if you want to figure out how much is the Earth accelerating from that force, you'... | Introduction to gravity Centripetal force and gravitation Physics Khan Academy.mp3 |
Imagine that I'm standing here holding the end of a rope. I'm over here on the left end, and while holding the rope, I rapidly move my hand up, down, and back to the starting position. If we were to take a snapshot of the rope immediately after I finish my motion, we're going to see something like this. The rope has a ... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
The rope has a squiggly disturbance that mirrors the motion I made with my hand, up, down, and back to the middle. And the rest of the rope is still flat. You might have seen something like this if you've ever played with a jump rope and wiggled it back and forth, or a slinky and you've seen that oscillate back and for... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
And we know that over time, this disturbance is actually going to make its way through the rope. If this is what we observe right after my hand motion, at some later point in time, we will observe that the beginning of the rope is back to its original shape, this squiggly disturbance has made its way further down the r... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
A wave is a disturbance, in this case, the squiggle in the rope caused by my hand motion, and that disturbance can propagate, it can travel or move in a particular direction. So a wave is a disturbance that can propagate. This particular example is called a mechanical wave. It's called a mechanical wave because the dis... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
It's called a mechanical wave because the disturbance is traveling through a medium, in this case, the rope. So mechanical waves travel through a medium. One important point about waves that is worth noting right now is that waves transfer energy without transferring matter. So what that means is that the disturbance t... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
So what that means is that the disturbance that is moving here, this squiggly shape, is moving through the rope, but it isn't moving the rope to a different position. Any part of the rope might go up and down as a wave travels through that section, but the rope itself is not going anywhere. Rather, it's the kinetic ene... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
So waves transfer energy but not matter. So in my first example, I only jerked my hand up and down once, which created a single wave pulse that moved through my rope. If instead I were to keep moving my hand up and down consistently, I would see a waveform that looks something like this. And when we model a wave, there... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
And when we model a wave, there are a few key characteristics that we need to know about that wave. First is the period. Period is measured in seconds, and it tells us how long it takes for one wave cycle to complete. Next is the wavelength. Measured in units of distance, like meters, the wavelength is the distance bet... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
Next is the wavelength. Measured in units of distance, like meters, the wavelength is the distance between identical points of adjacent waves. And finally, there's frequency. So the waveform that we've drawn here takes one second. There are four cycles in that one second. That means it has a frequency of four Hertz, or... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
So the waveform that we've drawn here takes one second. There are four cycles in that one second. That means it has a frequency of four Hertz, or four cycles per second. So the frequency, measured in cycles per second, tells us how many wave cycles there are every second. Now using just these basic anatomical propertie... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
So the frequency, measured in cycles per second, tells us how many wave cycles there are every second. Now using just these basic anatomical properties of a wave, we can start to figure out more interesting physical characteristics, like speed or distance over time. If we want to know how fast a wave is traveling, we c... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
The cycles cancel out, and we're left with units of distance over time, the same as speed. And that's our equation for the speed of the wave, wavelength times frequency. The standard units for speed are meters per second. There are a couple factors that can affect the speed of a wave. The first is the wave type. So dif... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
There are a couple factors that can affect the speed of a wave. The first is the wave type. So different types of waves move at different speeds. A relatable example of different waves moving at different speeds is lightning. If you've ever seen lightning strike or been in a thunderstorm, you know that the first thing ... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
A relatable example of different waves moving at different speeds is lightning. If you've ever seen lightning strike or been in a thunderstorm, you know that the first thing you see is the flash of lightning. And then you hear the thunder associated with that lightning flash. So the lightning comes first, and the thund... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
So the lightning comes first, and the thunder comes second. That's because those are two different waves that are part of the same phenomenon. When the lightning strike hits, you see the flash first because that's an electromagnetic wave, light. It travels much faster than the sound associated with the lightning strike... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
It travels much faster than the sound associated with the lightning strike. Electromagnetic waves are special not only because they travel really fast, but they also don't need a medium to travel through. The thunder, on the other hand, is a sound wave, traveling slower than the light. So you'll see the lightning befor... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
So you'll see the lightning before you hear the thunder. Different wave types move at different speeds. The second key factor that can affect the speed of a wave is the medium through which the wave travels. And we'll consider sound as an example here. So when someone is talking, right, we have this talking head creati... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
And we'll consider sound as an example here. So when someone is talking, right, we have this talking head creating some vibrations of the particles in front of their mouth. That's the sound wave. It's the vibration of those particles propagating through the air. When you speak, your vocal cords exert force on the parti... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
It's the vibration of those particles propagating through the air. When you speak, your vocal cords exert force on the particles just in front of you. They vibrate back and forth, creating a compression that transfers to the surrounding particles. As the vibrations continue to propagate, the sound travels. You can imag... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
As the vibrations continue to propagate, the sound travels. You can imagine that if these particles are packed closer together, those vibrations are going to transfer a lot more quickly because the particles are colliding much faster than if they're further apart. So sound travels much faster in water, a liquid, than i... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
The particles in the liquid are closer together. Since they're closer compacted, they collide more and the propagation of the wave happens faster. So different waves move at different speeds and the medium through which a wave travels can also affect the speed of a wave. All right, so let's try to summarize all this in... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
All right, so let's try to summarize all this information. We have waves, a wave, a disturbance that can propagate, and it has a few key characteristics. There's the period, or how long it takes one cycle to complete. There's the wavelength, the distance between identical points on two waves that are next to each other... | Wave properties Wave properties High School Physics Khan Academy.mp3 |
Energy is a word we hear all the time in seemingly different contexts almost every single day. We hear about renewable energy on the news, and particularly in the winter we hear people talking about their energy bills because they're worried about how much it's going to cost to heat their homes. So this brings about th... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
So in physics we actually have a specific definition of what energy is, and you'll see it's really not that different from how we talk about energy day to day. Energy in physics is defined as the ability to do work. We can't talk about energy without talking about work, so we should probably define that right now. Beca... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
Because work is another one of these words that we use an awful lot, but once again physics has a specific definition for it. In physics, work is performed when you apply force over a distance. We can actually write this as an equation, W equals F times D, where W is work, F is force, and D is distance or displacement.... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
If you've ever moved a box, a suitcase, or really any object in your room across the floor just to get out of your way, you performed work. You had to apply force to that box to move it whatever distance it took to get out of your way. If it was a short distance, you can see from the equation that that's going to be le... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
And in order to perform this work to move the box out of your way, you had to have energy available. That energy is enabling you to do the work because you're going to transfer the energy from yourself to that box in order to move it. So another way that we can think about work and energy is that the change in energy o... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
When we define energy this way, it allows us to do a lot of interesting things. We've set up a way to measure and calculate energy, so it's actually a quantifiable property. Let's go back to the example of a box, and let's say that instead of just trying to move a box out of your way in your room, you're actually going... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
And now you have 10 boxes to move. We can actually calculate the energy required to move all of those boxes. You might be saying to yourself, wait a minute, I'm now moving 10 boxes. That actually sounds kind of tiring. And if I'm getting tired, does that mean I'm actually losing energy? It turns out that energy is comi... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
That actually sounds kind of tiring. And if I'm getting tired, does that mean I'm actually losing energy? It turns out that energy is coming from somewhere, and in this case it's going to come from food. So as you're moving these boxes, you may find yourself getting hungry. So you should probably grab a snack, somethin... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
So as you're moving these boxes, you may find yourself getting hungry. So you should probably grab a snack, something like, I don't know, an apple. Let's pretend that's what I've drawn there. So that you can get more energy to move the rest of those 10 boxes. And you might be thinking now, wait a minute, this energy co... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
So that you can get more energy to move the rest of those 10 boxes. And you might be thinking now, wait a minute, this energy coming from food to me seems different than energy between me and moving a box. And that's because you can actually see the box moving. Which brings us to our next point. Energy comes in various... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
Which brings us to our next point. Energy comes in various forms, and they don't all look the same. We have equations to quantify the energy of these various forms, and we'll talk about those in another video. But the key here is that energy can transfer between objects, and it can also convert between different forms,... | What is energy Introduction to energy High school physics Khan Academy.mp3 |
So in either of these cases, these things are going to repel each other. But if they have different charges, they're going to attract each other. So if I have a positive and I have a negative, they're going to attract each other. This charge is this property of matter that we've started to observe, and we've started to... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
This charge is this property of matter that we've started to observe, and we've started to observe of how these different charges, this framework that we've created, how these things start to interact with each other. So these things are going to, these two things are going to attract each other. But the question is, w... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
And this was a question people have noticed, I guess what you could call electrostatics for a large swath of recorded human history, but it wasn't until the 1600s and especially the 1700s that people started to seriously view this as something that they could manipulate and even start to predict in a kind of serious ma... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
And so in Coulomb's Law, what it states is, is if I have two charges, so let me, so let's say this charge right over here, and I'm going to make it in white because it could be positive or negative, but I'll just make it q1, it has some charge. And then I have in Coulomb's, and then another charge, q2 right over here, ... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
He stated that the magnitude of the electrostatic force is proportional to the product of the magnitudes of the charges. I could write this as Q1 times Q2 and I could take the absolute value of each, which is the same thing as just taking the absolute value of the product. Here's why I'm taking the absolute value of th... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
Well, if they're different charges, this will be a negative number, but we just want the overall magnitude of the force. We could take, it's proportional to the absolute value of the product of the charges and it's inversely proportional to not just the distance between them, not just to R, but to the square of the dis... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
Newton's Law of Gravitation, we know that the force due to gravity between two masses, remember mass is just another property of matter that we sometimes feel is a little bit more tangible because it feels like we can kind of see weight and volume, but that's not quite the same, or we feel like we can feel or internali... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So let's say that I have a charge here, let's say that I have a charge here, and it has a positive charge of, I don't know, let's say it is positive five times 10 to the negative three Coulombs, so that's this one right over here, that's its charge. And let's say I have this other charge right over here, and this has a... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So given that, let's figure out what the electrostatic force between these two are going to be. And we can already predict that it's going to be an attractive force because they have different signs, and that was actually part of Coulomb's Law. This is the magnitude of the force. If these have different signs, it's att... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
If these have different signs, it's attractive. If they have the same sign, then they are going to repel each other. And I know what you're saying, well in order to actually calculate it, I need to know what k is. What is this electrostatic constant, what is this electrostatic constant going to actually be? And so you ... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
What is this electrostatic constant, what is this electrostatic constant going to actually be? And so you can measure that with a lot of precision, and we have kind of modern numbers on it, but the electrostatic constant, especially for the sake of this problem, I mean if we were to get really precise, it's 8.987551, w... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
I won't have to get a calculator out. Let's just say it's approximately nine times 10 to the ninth. Nine times 10 to the ninth. Nine times, actually let me make sure it says approximately, because I am approximating here. Nine times 10 to the ninth. And what are the units going to be? Well in the numerator here, when I... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
Nine times, actually let me make sure it says approximately, because I am approximating here. Nine times 10 to the ninth. And what are the units going to be? Well in the numerator here, when I multiply Coulombs times Coulombs, I'm going to get Coulomb squared. This right over here is going to give me, that's going to g... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
Well in the numerator here, when I multiply Coulombs times Coulombs, I'm going to get Coulomb squared. This right over here is going to give me, that's going to give me Coulombs squared. And this down over here is going to give me meters squared. This is going to give me meters squared. And what I want is to get rid of... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
This is going to give me meters squared. And what I want is to get rid of the Coulombs and the meters and end up with just Newtons. And so the units here are actually, the units here are Newtons, Newton and then meters squared, and that cancels out with the meters squared in the denominator. Newton meters squared over ... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
Newton meters squared over Coulombs squared. Over Coulombs squared. Let me do that in white. Over Coulombs squared. So these meters squared will cancel with those, those Coulombs squared in the denominator over here will cancel with those and you'll be just left with Newtons. But let's actually do that. Let's actually ... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
Over Coulombs squared. So these meters squared will cancel with those, those Coulombs squared in the denominator over here will cancel with those and you'll be just left with Newtons. But let's actually do that. Let's actually apply it to this example. And I encourage you to pause the video and apply this information t... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
Let's actually apply it to this example. And I encourage you to pause the video and apply this information to Coulombs law and figure out what the electrostatic force between these two particles is going to be. So I'm assuming you've had your go at it. So it is going to be, this is really just applying the formula. It'... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So it is going to be, this is really just applying the formula. It's going to be nine times 10 to the ninth. Nine times 10 to the ninth. And I'll write the units here. Newtons meters squared over Coulombs squared. And then Q one times Q two. So this is going to be, let's see, this is going to be, actually let me just w... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
And I'll write the units here. Newtons meters squared over Coulombs squared. And then Q one times Q two. So this is going to be, let's see, this is going to be, actually let me just write it all out for this first time. So it's going to be times five times 10 to the negative 30 Coulombs times negative one times 10 to t... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So this is going to be, let's see, this is going to be, actually let me just write it all out for this first time. So it's going to be times five times 10 to the negative 30 Coulombs times negative one times 10 to the negative one Coulombs. And we're going to take the absolute value of this so that negative is going to... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
All of that over, all of that over, we're in kind of the home stretch right over here, 0.5 meters squared. 0.5 meters squared. And so let's just do a little bit of the math here. So first of all, let's look at the units. So we have Coulombs squared here and then we're going to have Coulombs times Coulombs there. So tha... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So first of all, let's look at the units. So we have Coulombs squared here and then we're going to have Coulombs times Coulombs there. So that's Coulombs squared divided by Coulombs squared. That's going to cancel with that and that. You have meters squared here. And actually let me just write it out. So the numerator,... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
That's going to cancel with that and that. You have meters squared here. And actually let me just write it out. So the numerator, in the numerator we are going to have, so if we just say nine times five times, well we take the absolute value, it's just going to be one. So nine times five is going to be, nine times five... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So the numerator, in the numerator we are going to have, so if we just say nine times five times, well we take the absolute value, it's just going to be one. So nine times five is going to be, nine times five times negative one. Five times negative one is negative five with the absolute value there. So it's just going ... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So it's just going to be five times nine. So it's going to be 45 times 10 to the nine minus three minus one. So six, five. So that's going to be 10 to the fifth. 10 to the fifth. The Coulombs already canceled out and we're going to have Newton meters squared over 0.25 meters squared. These cancel. | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
So that's going to be 10 to the fifth. 10 to the fifth. The Coulombs already canceled out and we're going to have Newton meters squared over 0.25 meters squared. These cancel. And so we are left with, well if you divide by 0.25, that's the same thing as dividing by 1 4th which is the same thing as multiplying by four. ... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
These cancel. And so we are left with, well if you divide by 0.25, that's the same thing as dividing by 1 4th which is the same thing as multiplying by four. So if you multiply this times four, 45 times four is 160 plus 20 is equal to 180 times 10 to the fifth Newtons. And if we wanted to write it in scientific notatio... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
And if we wanted to write it in scientific notation, well we could divide this by 100 and then multiply this by 100 and so you could write this as 1.80 times, and actually I don't want to make it look like I have more significant digits than I really have, 1.8 times 10 to the seventh Newtons. I just divided this by 100... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
This is the magnitude of the electrostatic force between those two particles. And it looks like it's fairly significant. This is actually a good amount, and that's because this is actually a good amount of charge, a lot of charge, especially at this distance right over here. And the next thing we have to think about, w... | Coulomb's Law Electrostatics Electrical engineering Khan Academy.mp3 |
That if you do nothing to this moving object on its own, this object is going to come to a stop. It is going to come to rest. And on the other side of things, if you want to keep an object moving, you have to keep applying a force to it. We've never in our everyday experience seen an object that just keeps moving on an... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
We've never in our everyday experience seen an object that just keeps moving on and on and on forever without anyone acting on it. It seems like something will always stop. And this is why for most of human history, probably prehistory, but we definitely know the ancient Greeks all the way until the 1600s, all the way ... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
Objects have a tendency to come to rest or to stop. And if you want to keep them moving, if you want to keep them moving, you have to apply some type of a net force to it. Apply force. And once again, this is completely consistent with everyday human experience. This is what we've all experienced our entire lives. But ... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
And once again, this is completely consistent with everyday human experience. This is what we've all experienced our entire lives. But then these gentlemen show up in the 1600s. And you might be surprised to see three gentlemen pictured here because this was about Newton's first law of motion. And indeed, one of these ... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
And you might be surprised to see three gentlemen pictured here because this was about Newton's first law of motion. And indeed, one of these gentlemen is Sir Isaac Newton. That's Newton right over there. But these other two guys get at least as much credit for it because they actually described really what Newton's fi... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
But these other two guys get at least as much credit for it because they actually described really what Newton's first law describes, and they did it before Newton. This is Galileo, Galileo, Galilei, and this is Rene Descartes. And they described it in different ways, and Newton frankly gets the credit for it because h... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
And their big insight, and it was very unintuitive at the time, so now we come to the 1600s, is that these three gentlemen said maybe it works the other way. Maybe objects have a tendency to maintain their velocity, so their speed and their direction, have a tendency to maintain their velocity. And if their speed is ze... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
Unless acted on by unbalanced force. So completely the opposite way of thinking. For 2,000 years, objects tend to stop on their own. If you want to keep them moving, apply a force. These guys say objects have a tendency to maintain their motion forever, and the only way that you're going to stop them is if you act on o... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
If you want to keep them moving, apply a force. These guys say objects have a tendency to maintain their motion forever, and the only way that you're going to stop them is if you act on or accelerate them or change their velocity, so either their speed or direction some way, is to act on them with an unbalanced force. ... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
You just went through this. You said for most of human history, including my own personal history, this is what I observed. How can these guys say that this thing has a tendency to go on forever? This seems to break down. And their big insight was, well, maybe these things don't have by themselves a tendency to stop, b... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
This seems to break down. And their big insight was, well, maybe these things don't have by themselves a tendency to stop, but because of interactions with their environment, forces are being generated that are acting against their motion. So when you think you're just leaving this thing alone, there's actually a net f... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
And this particular example right over here, the net force is the force of friction. It's the interaction between the block and the ground. So when you think that you're leaving this thing alone, you actually have a net force that is going against its motion, which is the force of friction. And these guys realized that... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
And these guys realized that because they said, look, if it was an innate property of the block, regardless of the environment, it should kind of always come to a stop in maybe a similar way. But they saw if you made this surface a little bit smoother and a little bit smoother, this thing would travel further and furth... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
And they didn't have the luxury of launching satellites and doing things in deep space. So it was a very, very, very unintuitive thought experiment. And then you might say, well, what about this other thing? What happens when I am applying a force? Because in my everyday life, if I want to drag my TV set across the roo... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
What happens when I am applying a force? Because in my everyday life, if I want to drag my TV set across the room, I apply a force to it. And what these guys would tell you is all you were doing, if you were keeping the velocity of that TV constant, all you were doing was counteracting this net negative force. So if th... | Newton's first law of motion Forces and Newton's laws of motion Physics Khan Academy.mp3 |
I am smelling pizza as it's in the oven. It's on my mind. And I know we're supposed to be talking about heat and thermal equilibrium, but I think we can make this work. Now, if you're impatient like me, you probably put a slice of pizza on your plate as soon as it comes out of the oven, and you've probably noticed that... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
Now, if you're impatient like me, you probably put a slice of pizza on your plate as soon as it comes out of the oven, and you've probably noticed that the bottom of the plate warms up. So let's think about what's going on here. We have the temperature of the pizza, T pizza, which is warmer than the temperature of our ... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
So since the temperature of the pizza is higher than that of the plate, the plate starts to warm up. The pizza's temperature, on the other hand, will actually start to lower. And this will happen anytime the temperature of object one isn't the same as temperature of object two. We know temperature is how we express if ... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
We know temperature is how we express if something is hot or cold. What does hot or cold mean? Temperature is actually the measure of the average kinetic energy of the particles in an object. So let's digest that for a second and break it down. So temperature, temperature, is the average kinetic energy of particles. An... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
So let's digest that for a second and break it down. So temperature, temperature, is the average kinetic energy of particles. And kinetic energy, as we know, is one half mv squared. So when the pizza is warm, its particles are moving faster than if it was cold. And when particles and objects are moving, they're actuall... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
So when the pizza is warm, its particles are moving faster than if it was cold. And when particles and objects are moving, they're actually vibrating around. So what's happening in the hotter object is that the particles are vibrating faster than when the object is colder. And that's what it means to be hot or cold. Th... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
And that's what it means to be hot or cold. This type of kinetic energy, the motion of particles, is also known as thermal energy. Now you might be wondering if temperature is the measure of kinetic energy in objects and we have the pizza on the plate with their temperatures changing, does this mean there's some sort o... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
And you would be spot on. Heat is the transfer of energy between objects at different temperatures. This is a really important concept, so let's write that definition out. Heat is the transfer of energy between objects at different temperatures. As you can see with our pizza and plate, heat is transferring from the hot... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
Heat is the transfer of energy between objects at different temperatures. As you can see with our pizza and plate, heat is transferring from the hot pizza to the cold plate, from the hot object to the cold object. Why is that? Well, let's go ahead and break down our problem and really dig into what's happening with eve... | Heat transfer Thermodynamics High school physics Khan Academy.mp3 |
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