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In this video, we're going to talk about analog versus digital. Something that's analog can be any value within a given range, while something digital is represented by a number of discrete or separate levels. To distinguish these two ideas, I like to think about clocks. An analog clock has the numbers in the hands, and it's analog because the motion of those hands is continuous. They can sweep across the circle, representing any of infinite times on that clock. For example, between 3.06 and 3.07, the minute hand is actually going to be at some point between those marks on the clock, showing one of the infinitely possible times that the clock can represent. Compare that to a digital clock.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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An analog clock has the numbers in the hands, and it's analog because the motion of those hands is continuous. They can sweep across the circle, representing any of infinite times on that clock. For example, between 3.06 and 3.07, the minute hand is actually going to be at some point between those marks on the clock, showing one of the infinitely possible times that the clock can represent. Compare that to a digital clock. A digital clock is only going to show you 3.06 or 3.07. It will never display any of the many fractional seconds between those two times. Digital only takes on certain discrete values, and it has a finite number of those values.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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Compare that to a digital clock. A digital clock is only going to show you 3.06 or 3.07. It will never display any of the many fractional seconds between those two times. Digital only takes on certain discrete values, and it has a finite number of those values. So an analog wave or signal will smoothly sweep across the infinitely many possible values it has, while a digital wave or signal will only be at one of a number of discrete values, so the shape of the wave will be more square or step-like. Let's check out an example so this makes a little more sense. I like music, so we're going to talk about sound.
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Digital only takes on certain discrete values, and it has a finite number of those values. So an analog wave or signal will smoothly sweep across the infinitely many possible values it has, while a digital wave or signal will only be at one of a number of discrete values, so the shape of the wave will be more square or step-like. Let's check out an example so this makes a little more sense. I like music, so we're going to talk about sound. Sound is an analog signal or wave. So if we look at a graph of sound, volume over time, it's going to have a smooth, continuous analog waveform. Both the amplitude, or the volume, and the frequency, what we hear as pitch, are changing continuously between infinite possible values.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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I like music, so we're going to talk about sound. Sound is an analog signal or wave. So if we look at a graph of sound, volume over time, it's going to have a smooth, continuous analog waveform. Both the amplitude, or the volume, and the frequency, what we hear as pitch, are changing continuously between infinite possible values. And that's because sound waves, the vibration of particles propagating through the air, actually changes continuously. The very first sound recording and reproduction technology imprinted that analog wave directly onto a material. For example, records imprint that sound wave into vinyl, and cassettes imprint the sound wave onto tape.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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Both the amplitude, or the volume, and the frequency, what we hear as pitch, are changing continuously between infinite possible values. And that's because sound waves, the vibration of particles propagating through the air, actually changes continuously. The very first sound recording and reproduction technology imprinted that analog wave directly onto a material. For example, records imprint that sound wave into vinyl, and cassettes imprint the sound wave onto tape. A major drawback of this technology is that for the sound to play back exactly as it was recorded, that waveform needs to stay untouched, right? So think about scratching vinyl, or stretching or smudging a cassette tape. That's directly deforming the wave, so you'll never be able to reproduce the sound exactly as it was recorded.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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For example, records imprint that sound wave into vinyl, and cassettes imprint the sound wave onto tape. A major drawback of this technology is that for the sound to play back exactly as it was recorded, that waveform needs to stay untouched, right? So think about scratching vinyl, or stretching or smudging a cassette tape. That's directly deforming the wave, so you'll never be able to reproduce the sound exactly as it was recorded. So technology advanced, and sound waves became digitized. Here's how. Alright, so recall our analog sound wave.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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That's directly deforming the wave, so you'll never be able to reproduce the sound exactly as it was recorded. So technology advanced, and sound waves became digitized. Here's how. Alright, so recall our analog sound wave. We have a smooth analog wave that's taking on any number of infinitely possible values within this range. In order to digitize this wave, we're going to ascribe numbers to the amplitude at different points. Alright?
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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Alright, so recall our analog sound wave. We have a smooth analog wave that's taking on any number of infinitely possible values within this range. In order to digitize this wave, we're going to ascribe numbers to the amplitude at different points. Alright? Watch this magic. So we go over here and make a scale. So we're breaking up the amplitudes into discrete possibilities.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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Alright? Watch this magic. So we go over here and make a scale. So we're breaking up the amplitudes into discrete possibilities. Then we can go through the wave, and at specific points of the wave, measure what is the amplitude based on that scale. So over here, we're at the first point of the scale. At this peak, we're at the second point of our scale.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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So we're breaking up the amplitudes into discrete possibilities. Then we can go through the wave, and at specific points of the wave, measure what is the amplitude based on that scale. So over here, we're at the first point of the scale. At this peak, we're at the second point of our scale. Then the first, the third, the second, the fourth, back down to the first. Now that we have this wave broken up into discrete levels, right, we can ascribe the numbers and we effectively turn this analog wave into a set of numbers. One, two, one, three, two, four, one.
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At this peak, we're at the second point of our scale. Then the first, the third, the second, the fourth, back down to the first. Now that we have this wave broken up into discrete levels, right, we can ascribe the numbers and we effectively turn this analog wave into a set of numbers. One, two, one, three, two, four, one. Our wave has been digitized. Now that digitized wave can be played back through a speaker to recreate the analog wave. As long as the sampling happens at a quick enough rate, humans can't tell the difference.
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One, two, one, three, two, four, one. Our wave has been digitized. Now that digitized wave can be played back through a speaker to recreate the analog wave. As long as the sampling happens at a quick enough rate, humans can't tell the difference. Alright? So the digitization of waves is all about ascribing specific numbers to some of those mechanical properties of the wave. The important thing here is that now that the wave has been digitized, the digitized sound wave can be reliably stored, processed, and communicated with computers.
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Digital and analog information Information Technologies High School Physics Khan Academy.mp3
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As long as the sampling happens at a quick enough rate, humans can't tell the difference. Alright? So the digitization of waves is all about ascribing specific numbers to some of those mechanical properties of the wave. The important thing here is that now that the wave has been digitized, the digitized sound wave can be reliably stored, processed, and communicated with computers. So some information is lost in translation, but once the wave is digitized, its quality will never degrade. Okay? This allows for a lot more reliable technology because the wave is represented with numbers instead of it being physically imprinted on some material.
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Hello everyone, let's talk about potential energy. Potential energy is energy that is stored in an object and this energy is related to the potential or the future possibility for an object to have a different type of energy like kinetic energy for motion that is converted from that potential energy. There are many kinds of potential energy, but they all arise from an object's relation to a position or an original shape. So while in general there are many different types of potential energy, there are several specific types that are very common, so let's talk about these. Gravitational potential energy is the potential energy that an object with mass has due to the force of gravity from another object with mass, like say the Earth. And in fact we often use the surface of the Earth to compare an object's position with to see how much potential energy it has in the Earth's gravitational field. Gravity is an attractive force, so objects with mass want to move towards the surface of the Earth.
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So while in general there are many different types of potential energy, there are several specific types that are very common, so let's talk about these. Gravitational potential energy is the potential energy that an object with mass has due to the force of gravity from another object with mass, like say the Earth. And in fact we often use the surface of the Earth to compare an object's position with to see how much potential energy it has in the Earth's gravitational field. Gravity is an attractive force, so objects with mass want to move towards the surface of the Earth. If we move them further away or opposite the direction of the gravitational force, we increase their gravitational potential energy, and the opposite is true if it gets closer. When an object is on the surface of Earth, we typically say it has no potential energy, but you could use any point to be this comparison where potential energy is zero. Consider a book on a bookshelf.
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Gravity is an attractive force, so objects with mass want to move towards the surface of the Earth. If we move them further away or opposite the direction of the gravitational force, we increase their gravitational potential energy, and the opposite is true if it gets closer. When an object is on the surface of Earth, we typically say it has no potential energy, but you could use any point to be this comparison where potential energy is zero. Consider a book on a bookshelf. If the book is on this shelf, we can use this shelf as the 0.4 potential energy. Moving it to a higher shelf would mean it has gravitational potential energy relative to that lower shelf, or relative to the floor if we want to use that as our comparison instead. Next we have elastic potential energy, which is the potential energy some objects have due to their shape being changed.
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Consider a book on a bookshelf. If the book is on this shelf, we can use this shelf as the 0.4 potential energy. Moving it to a higher shelf would mean it has gravitational potential energy relative to that lower shelf, or relative to the floor if we want to use that as our comparison instead. Next we have elastic potential energy, which is the potential energy some objects have due to their shape being changed. These types of objects are called elastic objects. Elastic objects are made of materials and designed so they have internal or inside forces that try to return them to their original shape. One very common example of this is a spring.
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Next we have elastic potential energy, which is the potential energy some objects have due to their shape being changed. These types of objects are called elastic objects. Elastic objects are made of materials and designed so they have internal or inside forces that try to return them to their original shape. One very common example of this is a spring. When you stretch or compress a spring, you change its shape, and the shape of the spring causes internal forces that try to return the spring to its original shape. Now electric potential energy, which is the potential energy a charged object has due to the electric force from another charged object. Opposite electric charges are attracted to one another, and similar electric charges are repelled, so the potential energy depends on what type of charges there are and how far apart they are.
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One very common example of this is a spring. When you stretch or compress a spring, you change its shape, and the shape of the spring causes internal forces that try to return the spring to its original shape. Now electric potential energy, which is the potential energy a charged object has due to the electric force from another charged object. Opposite electric charges are attracted to one another, and similar electric charges are repelled, so the potential energy depends on what type of charges there are and how far apart they are. Potential energy increases when the charges move opposite the direction of the electric force, for example when two negative charges get closer together. Similarly, magnetic potential energy is the potential energy a magnetic object has due to the magnetic force from another magnet. Magnetic force causes similar poles to repel one another and opposite poles to attract, and because magnets have north and south poles, the potential energy depends not only on the position within a field, but also the magnet's orientation.
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Opposite electric charges are attracted to one another, and similar electric charges are repelled, so the potential energy depends on what type of charges there are and how far apart they are. Potential energy increases when the charges move opposite the direction of the electric force, for example when two negative charges get closer together. Similarly, magnetic potential energy is the potential energy a magnetic object has due to the magnetic force from another magnet. Magnetic force causes similar poles to repel one another and opposite poles to attract, and because magnets have north and south poles, the potential energy depends not only on the position within a field, but also the magnet's orientation. Again, you could increase the potential energy by moving the magnets opposite the direction of the magnetic force, for example by pulling apart a north pole and a south pole. All of these types of energy are due to different forces and are calculated differently from different equations, which we won't cover here, but they are all potential energy. And these are just a few of the most common types of potential energy, but there are more.
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Magnetic force causes similar poles to repel one another and opposite poles to attract, and because magnets have north and south poles, the potential energy depends not only on the position within a field, but also the magnet's orientation. Again, you could increase the potential energy by moving the magnets opposite the direction of the magnetic force, for example by pulling apart a north pole and a south pole. All of these types of energy are due to different forces and are calculated differently from different equations, which we won't cover here, but they are all potential energy. And these are just a few of the most common types of potential energy, but there are more. In summary, potential energy is the stored energy in an object due to its position, its properties, and the forces acting on it. Potential energy is measured relative to some comparison position or shape and describes the potential for other forms of energy, commonly kinetic energy for motion, to exist. There are many forms of potential energy, including gravitational, elastic, magnetic, and electric.
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And this is also known as Newton's third law of motion, but it's also one of the most misunderstood laws of physics. So that's why we're going to dig into it a little bit in this video. So I have two examples here where Newton's third law or this notion of an action and a reaction force is happening. So over here, you have this plane flying and the plane is able to move forward by pushing air particles through these jet engines. So these air particles are pushed outward at a very, very high velocity out the back of the engines. If you were to enlarge one of those air particles, let's say this is this purple dot right over here, there is a force that is being exerted on it by the jet engine. And that force is going in that direction.
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So over here, you have this plane flying and the plane is able to move forward by pushing air particles through these jet engines. So these air particles are pushed outward at a very, very high velocity out the back of the engines. If you were to enlarge one of those air particles, let's say this is this purple dot right over here, there is a force that is being exerted on it by the jet engine. And that force is going in that direction. So what is the equal and opposite reaction force? Well, the equal and opposite reaction force is not also occurring on that molecule, it's what the molecule is doing to the plane. The equal and opposite reaction force is that the molecule is going to be pushing on the jet engine with an equal, but an opposite force.
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And that force is going in that direction. So what is the equal and opposite reaction force? Well, the equal and opposite reaction force is not also occurring on that molecule, it's what the molecule is doing to the plane. The equal and opposite reaction force is that the molecule is going to be pushing on the jet engine with an equal, but an opposite force. So it's going to go in the opposite direction. And that's how the jet is able to accelerate forward by pushing on these particles and accelerating them backward by exerting a force on them. The equal and opposite force is the force that the particles, those molecules of air are exerting on the jet and moving it forward.
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The equal and opposite reaction force is that the molecule is going to be pushing on the jet engine with an equal, but an opposite force. So it's going to go in the opposite direction. And that's how the jet is able to accelerate forward by pushing on these particles and accelerating them backward by exerting a force on them. The equal and opposite force is the force that the particles, those molecules of air are exerting on the jet and moving it forward. The same thing here is going on with this rocket. You have some rocket fuel in there, it gets ignited, it explodes. And as it explodes, there's a force that exerts on those little molecules.
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The equal and opposite force is the force that the particles, those molecules of air are exerting on the jet and moving it forward. The same thing here is going on with this rocket. You have some rocket fuel in there, it gets ignited, it explodes. And as it explodes, there's a force that exerts on those little molecules. And that force is going in this direction. But as it does that, there's an equal and opposite force that the molecules are exerting on the rocket. The rocket is having a force acted on it, once again, equal and opposite.
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And as it explodes, there's a force that exerts on those little molecules. And that force is going in this direction. But as it does that, there's an equal and opposite force that the molecules are exerting on the rocket. The rocket is having a force acted on it, once again, equal and opposite. So it's important to realize that the reaction force is not on the same object, it's on the other object. If one object is putting an action force on another, then the second object is putting a reaction force on the first. The forces do not cancel out.
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The rocket is having a force acted on it, once again, equal and opposite. So it's important to realize that the reaction force is not on the same object, it's on the other object. If one object is putting an action force on another, then the second object is putting a reaction force on the first. The forces do not cancel out. It's also important to realize that both forces are generated in pairs and happen at the exact same time. There's no delay. We can look at other examples of this.
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The forces do not cancel out. It's also important to realize that both forces are generated in pairs and happen at the exact same time. There's no delay. We can look at other examples of this. This is a scenario that I would never want to be caught in being drifting through space. Now, this astronaut here has some type of a rocket pack that might help it move around. But let's say your rocket pack ran out of fuel and you're just drifting through space.
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We can look at other examples of this. This is a scenario that I would never want to be caught in being drifting through space. Now, this astronaut here has some type of a rocket pack that might help it move around. But let's say your rocket pack ran out of fuel and you're just drifting through space. How can you get back to your spaceship? Well, if you have a wrench or something on you that you can throw, if you can take that wrench and if you can push that wrench in that direction, and let's say your spaceship is over here to the left, well, the equal and opposite force is the force that the wrench is going to exert on you, the astronaut, and then it will push you in that direction and accelerate you in that direction. So that's a useful thing if you ever get caught drifting through space.
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Action and reaction forces Movement and forces Middle school physics Khan Academy.mp3
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But let's say your rocket pack ran out of fuel and you're just drifting through space. How can you get back to your spaceship? Well, if you have a wrench or something on you that you can throw, if you can take that wrench and if you can push that wrench in that direction, and let's say your spaceship is over here to the left, well, the equal and opposite force is the force that the wrench is going to exert on you, the astronaut, and then it will push you in that direction and accelerate you in that direction. So that's a useful thing if you ever get caught drifting through space. But you could do an experiment right now. Press on the table in front of you. When you press on that table, you're clearly putting a force onto that table.
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Action and reaction forces Movement and forces Middle school physics Khan Academy.mp3
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So that's a useful thing if you ever get caught drifting through space. But you could do an experiment right now. Press on the table in front of you. When you press on that table, you're clearly putting a force onto that table. If your table is soft, you'll see it get compressed. But notice your finger itself is also getting compressed. And the whole reason why you can even feel that is because your finger is getting compressed.
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Action and reaction forces Movement and forces Middle school physics Khan Academy.mp3
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When you press on that table, you're clearly putting a force onto that table. If your table is soft, you'll see it get compressed. But notice your finger itself is also getting compressed. And the whole reason why you can even feel that is because your finger is getting compressed. And that is the equal and opposite force that the table is putting on your finger. And this can happen at very, very large distances as well. The whole reason why the moon is in orbit around the Earth is because there's a gravitational force of Earth's mass acting on the moon, but there's an equal and opposite force of the moon acting on Earth.
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Action and reaction forces Movement and forces Middle school physics Khan Academy.mp3
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And the whole reason why you can even feel that is because your finger is getting compressed. And that is the equal and opposite force that the table is putting on your finger. And this can happen at very, very large distances as well. The whole reason why the moon is in orbit around the Earth is because there's a gravitational force of Earth's mass acting on the moon, but there's an equal and opposite force of the moon acting on Earth. And it's actually not that the moon is rotating around the Earth. It's actually they're both rotating around the center of mass of their combination. That just happens to be so much closer to Earth.
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Action and reaction forces Movement and forces Middle school physics Khan Academy.mp3
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The whole reason why the moon is in orbit around the Earth is because there's a gravitational force of Earth's mass acting on the moon, but there's an equal and opposite force of the moon acting on Earth. And it's actually not that the moon is rotating around the Earth. It's actually they're both rotating around the center of mass of their combination. That just happens to be so much closer to Earth. It's actually within Earth's volume that it looks like the moon is rotating around the Earth. And this isn't just celestial bodies. I weigh 165 pounds.
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That just happens to be so much closer to Earth. It's actually within Earth's volume that it looks like the moon is rotating around the Earth. And this isn't just celestial bodies. I weigh 165 pounds. That is the force that Earth is acting on me due to gravity. But it turns out that there's an equal and opposite force of 165 pounds that I am pulling on Earth with. So I will leave you there.
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Action and reaction forces Movement and forces Middle school physics Khan Academy.mp3
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I weigh 165 pounds. That is the force that Earth is acting on me due to gravity. But it turns out that there's an equal and opposite force of 165 pounds that I am pulling on Earth with. So I will leave you there. Look around the world. This is happening everywhere. For every force, there's an equal and opposite reaction force.
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We do this by using units and frames of reference, which are also called reference frames. We talk about units in another video, so let's look at what a frame of reference is. Let's say this blue box thing is a car, and it's going 45 miles per hour. Someone standing on the side of the road would see it pass at 45 miles per hour. Now if this yellow truck is going 40 miles per hour, someone sitting in the yellow truck would observe the blue car traveling at five miles per hour. How could the person on the side of the road see the blue car traveling at 45 miles per hour, and a person in the yellow truck see the blue car moving at five miles per hour? This is because both observers are using different frames of reference.
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Someone standing on the side of the road would see it pass at 45 miles per hour. Now if this yellow truck is going 40 miles per hour, someone sitting in the yellow truck would observe the blue car traveling at five miles per hour. How could the person on the side of the road see the blue car traveling at 45 miles per hour, and a person in the yellow truck see the blue car moving at five miles per hour? This is because both observers are using different frames of reference. So let's go ahead and take a look at that, starting with the speed of the blue car. The person on the side of the road is using their frame of reference of being at rest, so relative to them, the blue car is moving at 45 miles per hour. To the person in this yellow truck, which remember is already going 40 miles per hour, the blue car is going five miles per hour.
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Frames of reference Movement and forces Middle school physics Khan Academy.mp3
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This is because both observers are using different frames of reference. So let's go ahead and take a look at that, starting with the speed of the blue car. The person on the side of the road is using their frame of reference of being at rest, so relative to them, the blue car is moving at 45 miles per hour. To the person in this yellow truck, which remember is already going 40 miles per hour, the blue car is going five miles per hour. Now let's do the exact same thing for the speed of the yellow truck. So what is the speed of the yellow truck for the observer on the side of the road? It's 40 miles per hour.
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To the person in this yellow truck, which remember is already going 40 miles per hour, the blue car is going five miles per hour. Now let's do the exact same thing for the speed of the yellow truck. So what is the speed of the yellow truck for the observer on the side of the road? It's 40 miles per hour. And what do you think the speed of the truck is for the person using their blue car as the reference frame? Well, the blue car is moving at 45 miles per hour, and the truck is only moving at 40 miles per hour. So the speed of the yellow truck is actually five miles per hour slower than this reference frame because the blue car is already moving at 45 miles per hour.
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It's 40 miles per hour. And what do you think the speed of the truck is for the person using their blue car as the reference frame? Well, the blue car is moving at 45 miles per hour, and the truck is only moving at 40 miles per hour. So the speed of the yellow truck is actually five miles per hour slower than this reference frame because the blue car is already moving at 45 miles per hour. Now you might be thinking, but wait, the person on the side of the road isn't really at rest. They're on the earth and the earth is moving. You're completely correct.
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So the speed of the yellow truck is actually five miles per hour slower than this reference frame because the blue car is already moving at 45 miles per hour. Now you might be thinking, but wait, the person on the side of the road isn't really at rest. They're on the earth and the earth is moving. You're completely correct. The person is at rest with respect to the earth, and the earth is the most common frame of reference that we use. To an observer in space who is not rotating with the earth, the blue car is going 45 miles per hour plus the speed of earth's rotation. And this is why frame of reference is so important.
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You're completely correct. The person is at rest with respect to the earth, and the earth is the most common frame of reference that we use. To an observer in space who is not rotating with the earth, the blue car is going 45 miles per hour plus the speed of earth's rotation. And this is why frame of reference is so important. We just talked about one blue car having three different velocities depending what the frame of reference is. How would we communicate this to avoid confusion? Well, we state the reference frame we're using.
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And this is why frame of reference is so important. We just talked about one blue car having three different velocities depending what the frame of reference is. How would we communicate this to avoid confusion? Well, we state the reference frame we're using. The blue car is moving at five miles per hour with respect to, which I'll write as WRT, the yellow truck. This tells us that the yellow truck is our frame of reference. Or we could say that the yellow truck is moving at 40 miles per hour and the blue car at 45 miles per hour with respect to the earth.
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And what we wanna do is we wanna start to move it. So what we do is we attach a rocket to one side and then we ignite that rocket and it starts to send all the superheated gas, all of these particles to the right. Well, what do you think that's going to do to the asteroid? Well, it's going to push on the asteroid in that direction or you could say it's going to exert a force on that asteroid. And we could show that force like this where the strength of that force or the magnitude of the force is the length of this line. And then the direction I will specify or show with that arrow. So fair enough, I will be pushing towards the left.
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Well, it's going to push on the asteroid in that direction or you could say it's going to exert a force on that asteroid. And we could show that force like this where the strength of that force or the magnitude of the force is the length of this line. And then the direction I will specify or show with that arrow. So fair enough, I will be pushing towards the left. And when I push to the left, it doesn't just start to move the asteroid to the left, it actually will accelerate the asteroid to the left. So the longer that this rocket is running, it's going to make the asteroid move to the left faster and faster and faster. But let's think about another example.
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So fair enough, I will be pushing towards the left. And when I push to the left, it doesn't just start to move the asteroid to the left, it actually will accelerate the asteroid to the left. So the longer that this rocket is running, it's going to make the asteroid move to the left faster and faster and faster. But let's think about another example. Let's say that you and one of your friends, you had a little bit of miscommunication and they went and put an identical rocket on this side of the asteroid and y'all ignited it at the exact same time. So this one is going to push in the other direction. What do you think is going to happen if these happened at the exact same time?
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But let's think about another example. Let's say that you and one of your friends, you had a little bit of miscommunication and they went and put an identical rocket on this side of the asteroid and y'all ignited it at the exact same time. So this one is going to push in the other direction. What do you think is going to happen if these happened at the exact same time? Even though there's now twice as much force being exerted on this asteroid, it's going in opposite directions. So they zero out and so there's zero net force. And so this asteroid won't be accelerated at all.
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Net force Movement and forces Middle school physics Khan Academy.mp3
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What do you think is going to happen if these happened at the exact same time? Even though there's now twice as much force being exerted on this asteroid, it's going in opposite directions. So they zero out and so there's zero net force. And so this asteroid won't be accelerated at all. Now let's say that a third friend wanted to correct this situation and this isn't necessarily the most efficient way to do it, but what they do is they put another identical rocket right over here and let's say ignite that. Now what will happen? Well, now you had the original two forces that net out to each other, but now you have this also this new force, which I will make in purple because it's a purple rocket.
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Net force Movement and forces Middle school physics Khan Academy.mp3
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And so this asteroid won't be accelerated at all. Now let's say that a third friend wanted to correct this situation and this isn't necessarily the most efficient way to do it, but what they do is they put another identical rocket right over here and let's say ignite that. Now what will happen? Well, now you had the original two forces that net out to each other, but now you have this also this new force, which I will make in purple because it's a purple rocket. And so that new force, you could draw like this to show, all right, that will now be the net force because you have the equivalent of two rockets going in the left direction and one rocket going in the right direction. Or another way we could draw that is we have two rockets going in the left direction. So that would have a force that looks like this.
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Net force Movement and forces Middle school physics Khan Academy.mp3
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Well, now you had the original two forces that net out to each other, but now you have this also this new force, which I will make in purple because it's a purple rocket. And so that new force, you could draw like this to show, all right, that will now be the net force because you have the equivalent of two rockets going in the left direction and one rocket going in the right direction. Or another way we could draw that is we have two rockets going in the left direction. So that would have a force that looks like this. And then we have one going in the right direction. And so if you were to net it out, this is equivalent to just having one rocket that we originally saw. That's equivalent to just going back to what we originally saw.
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Net force Movement and forces Middle school physics Khan Academy.mp3
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Let's talk about waves. So let's imagine that you were to take a string and attach it at one end to a wall, and then on the other end, you were to wiggle it up and down. Well, then you would have made a wave. You would see a pattern that looks like this. Now, what could be a good definition for a wave? Well, we could call it a traveling disturbance. Well, what does that mean?
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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You would see a pattern that looks like this. Now, what could be a good definition for a wave? Well, we could call it a traveling disturbance. Well, what does that mean? Well, we're disturbing the rope. If we didn't move it, if we just held it straight, it might look something like that, or it might just hang down a little bit, but clearly, we are now moving it up and down, and those movements are disturbing that rope, and that disturbance can move along that rope. Now, we see waves not just in ropes that are moving up and down.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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Well, what does that mean? Well, we're disturbing the rope. If we didn't move it, if we just held it straight, it might look something like that, or it might just hang down a little bit, but clearly, we are now moving it up and down, and those movements are disturbing that rope, and that disturbance can move along that rope. Now, we see waves not just in ropes that are moving up and down. You have probably seen water waves. If you were to take a tank of water like this, and if you were to start pressing on one end of the water here, you would see these waveforms that start. We can also see that with sound and sound waves.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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Now, we see waves not just in ropes that are moving up and down. You have probably seen water waves. If you were to take a tank of water like this, and if you were to start pressing on one end of the water here, you would see these waveforms that start. We can also see that with sound and sound waves. You might not realize it, but the sound of my voice right now is actually just a traveling compression or disturbance in the air that is getting to your ear, and then little hairs in your ears can sense those changes in pressure from the air, and your mind perceives that as sound, and once again, this is a traveling disturbance. You have particles that have high pressure, and then they knock into the particles next to them that then knock into the particles next to them, so if you were to be able to observe this in slow motion, you would see these high-pressure parts right over here could be traveling, say, to the right, and even though this might be a pressure wave that's traveling through the air, we can represent it in a way that looks a lot like our first rope that we were moving up and down. Areas where things are high, in the sound example, that's high pressure, and you have areas where things are low, in the sound example, that is low pressure.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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We can also see that with sound and sound waves. You might not realize it, but the sound of my voice right now is actually just a traveling compression or disturbance in the air that is getting to your ear, and then little hairs in your ears can sense those changes in pressure from the air, and your mind perceives that as sound, and once again, this is a traveling disturbance. You have particles that have high pressure, and then they knock into the particles next to them that then knock into the particles next to them, so if you were to be able to observe this in slow motion, you would see these high-pressure parts right over here could be traveling, say, to the right, and even though this might be a pressure wave that's traveling through the air, we can represent it in a way that looks a lot like our first rope that we were moving up and down. Areas where things are high, in the sound example, that's high pressure, and you have areas where things are low, in the sound example, that is low pressure. Now, when we talk about waves, there are common properties. For example, we might wanna know how much are we getting disturbed from what we would call the equilibrium. You could view that as maybe the middle state right over there.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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Areas where things are high, in the sound example, that's high pressure, and you have areas where things are low, in the sound example, that is low pressure. Now, when we talk about waves, there are common properties. For example, we might wanna know how much are we getting disturbed from what we would call the equilibrium. You could view that as maybe the middle state right over there. Well, if we're getting disturbed that much, we could call that the amplitude. That's how much we are going above or below that equilibrium. This would be the amplitude as well.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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You could view that as maybe the middle state right over there. Well, if we're getting disturbed that much, we could call that the amplitude. That's how much we are going above or below that equilibrium. This would be the amplitude as well. We could think about how far is it from the same points on the wave, so if we go from one peak to another peak, well, we could call that the wavelength, and you could just do it from any one point on the wave that's just like it on the wave again, so that would be the same wavelength as our original wavelength right over there. You might hear the term frequency of a wave, and one way to think about that is if you were to just observe our original rope, and if you were to say, how many times does it go all the way up, all the way down, and then back up, so it completes a full cycle, how many times can it do that in a second? If it does that five times in a second, then someone might say it has a frequency of five cycles per second.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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This would be the amplitude as well. We could think about how far is it from the same points on the wave, so if we go from one peak to another peak, well, we could call that the wavelength, and you could just do it from any one point on the wave that's just like it on the wave again, so that would be the same wavelength as our original wavelength right over there. You might hear the term frequency of a wave, and one way to think about that is if you were to just observe our original rope, and if you were to say, how many times does it go all the way up, all the way down, and then back up, so it completes a full cycle, how many times can it do that in a second? If it does that five times in a second, then someone might say it has a frequency of five cycles per second. Now, everything that we have just talked about, these are called mechanical waves. It's a special category, probably the ones that you will see most often. Now, mechanical waves need a medium to travel through.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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If it does that five times in a second, then someone might say it has a frequency of five cycles per second. Now, everything that we have just talked about, these are called mechanical waves. It's a special category, probably the ones that you will see most often. Now, mechanical waves need a medium to travel through. In the rope example, the medium was the rope. In the water example, it's the water. In the sound example, the medium is the air.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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Now, mechanical waves need a medium to travel through. In the rope example, the medium was the rope. In the water example, it's the water. In the sound example, the medium is the air. Now, there are things that can be described as waves that don't need a medium. In particular, and this is kind of mind-boggling, is that light can be considered a wave. If we think about the different frequencies of light, our brain perceives that as different colors, and if we think about the amplitude of light, our brain perceives that as the intensity of light, how bright it is.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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In the sound example, the medium is the air. Now, there are things that can be described as waves that don't need a medium. In particular, and this is kind of mind-boggling, is that light can be considered a wave. If we think about the different frequencies of light, our brain perceives that as different colors, and if we think about the amplitude of light, our brain perceives that as the intensity of light, how bright it is. And even more mind-blowing, visible light are just certain frequencies of what we would call electromagnetic waves. There's actually higher frequencies of electromagnetic waves that have all sorts of applications. You might've heard of ultraviolet light, or X-rays, or gamma rays.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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If we think about the different frequencies of light, our brain perceives that as different colors, and if we think about the amplitude of light, our brain perceives that as the intensity of light, how bright it is. And even more mind-blowing, visible light are just certain frequencies of what we would call electromagnetic waves. There's actually higher frequencies of electromagnetic waves that have all sorts of applications. You might've heard of ultraviolet light, or X-rays, or gamma rays. Similarly, there are lower wavelengths of light. You might've heard things like infrared or radio waves. These are all just different frequencies of what's known as electromagnetic waves.
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Mechanical waves and light Waves Middle school physics Khan Academy.mp3
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And when we're talking about data and measurements with other scientists, we need to make sure we're on the same page. So how do we do that? Well, one of the ways is to use units. We use units whenever we talk about things like position, where an object's located, how long it is. Its mass, how much matter it's made up of. Or its motion, how is that object moving? You probably hear units every day.
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Units Movement and forces Middle school physics Khan Academy.mp3
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We use units whenever we talk about things like position, where an object's located, how long it is. Its mass, how much matter it's made up of. Or its motion, how is that object moving? You probably hear units every day. For example, you've grown, let's say, an inch and a half in the past year. Or that tree over there is 25 feet tall. And maybe you went swimming in a 25 meter pool.
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Units Movement and forces Middle school physics Khan Academy.mp3
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You probably hear units every day. For example, you've grown, let's say, an inch and a half in the past year. Or that tree over there is 25 feet tall. And maybe you went swimming in a 25 meter pool. And we're just going to pretend that the pool is a rectangle, because as you can tell from my tree, my artistic skills are not that great. Anyway, this brings up a super important point about why we use units. I just used three examples of length measurements with three different units.
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Units Movement and forces Middle school physics Khan Academy.mp3
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And maybe you went swimming in a 25 meter pool. And we're just going to pretend that the pool is a rectangle, because as you can tell from my tree, my artistic skills are not that great. Anyway, this brings up a super important point about why we use units. I just used three examples of length measurements with three different units. Inches, feet, and meters. Imagine if I didn't attach a unit to any of these measurements. You grew one and a half what?
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Units Movement and forces Middle school physics Khan Academy.mp3
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I just used three examples of length measurements with three different units. Inches, feet, and meters. Imagine if I didn't attach a unit to any of these measurements. You grew one and a half what? Meters? Whoa. One and a half hands?
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Units Movement and forces Middle school physics Khan Academy.mp3
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You grew one and a half what? Meters? Whoa. One and a half hands? Well, whose hands? Your hands? Or my hands?
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Units Movement and forces Middle school physics Khan Academy.mp3
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One and a half hands? Well, whose hands? Your hands? Or my hands? Oof. Well, pretend those are hands. Units let us know how much of a quantity there is.
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Units Movement and forces Middle school physics Khan Academy.mp3
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Or my hands? Oof. Well, pretend those are hands. Units let us know how much of a quantity there is. So a meter is always used to measure length, and we know exactly how long a meter is. That way, when we say something is two meters long, no one has to guess at how big that is. Any measurement or data point always needs to have a unit, or else it's just a meaningless number.
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Units Movement and forces Middle school physics Khan Academy.mp3
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Units let us know how much of a quantity there is. So a meter is always used to measure length, and we know exactly how long a meter is. That way, when we say something is two meters long, no one has to guess at how big that is. Any measurement or data point always needs to have a unit, or else it's just a meaningless number. To avoid any confusion, in science we use what are called SI units. SI units are the International System. Could there be any more letters in this word?
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Units Movement and forces Middle school physics Khan Academy.mp3
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Any measurement or data point always needs to have a unit, or else it's just a meaningless number. To avoid any confusion, in science we use what are called SI units. SI units are the International System. Could there be any more letters in this word? System. Used by scientists all over the world. People use meters to describe position or length, kilograms for mass, and if we're talking about the motion of something, meters per second.
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Units Movement and forces Middle school physics Khan Academy.mp3
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Could there be any more letters in this word? System. Used by scientists all over the world. People use meters to describe position or length, kilograms for mass, and if we're talking about the motion of something, meters per second. And while this is the agreed upon scientific unit system, you should be aware that other systems do exist, which means things can very easily get very confusing if you forget your units. And you might be thinking, oh come on, who mixes up units? Well, it happens more often than you think.
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Units Movement and forces Middle school physics Khan Academy.mp3
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People use meters to describe position or length, kilograms for mass, and if we're talking about the motion of something, meters per second. And while this is the agreed upon scientific unit system, you should be aware that other systems do exist, which means things can very easily get very confusing if you forget your units. And you might be thinking, oh come on, who mixes up units? Well, it happens more often than you think. Even rocket scientists have done it. I mean, a Mars orbiter actually crashed due to a mix up in units. No seriously, that actually happened.
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Units Movement and forces Middle school physics Khan Academy.mp3
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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 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 forth on the ground, or if you've been in the gym and seen somebody doing exercises with large battle ropes, slamming them up and down repeatedly. And we know that over time, this disturbance is actually going to make its way through the rope.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 forth on the ground, or if you've been in the gym and seen somebody doing exercises with large battle ropes, slamming them up and down repeatedly. 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 rope, and it will keep traveling in this direction until it reaches the end of the rope. This is exactly what a wave is in physics. 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.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 rope, and it will keep traveling in this direction until it reaches the end of the rope. This is exactly what a wave is in physics. 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 disturbance is traveling through a medium, in this case, the rope.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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 that is moving here, this squiggly shape, is moving through the rope, but it isn't moving the rope to a different position.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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 energy imparted to the rope by my hand that is transferring from particle to particle and making its way through the rope. So waves transfer energy but not matter.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 energy imparted to the rope by my hand that is transferring from particle to particle and making its way through the rope. 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 are a few key characteristics that we need to know about that wave.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 between identical points of adjacent waves. And finally, there's frequency. So the waveform that we've drawn here takes one second.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 four cycles per second. So the frequency, measured in cycles per second, tells us how many wave cycles there are every second.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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 can take its wavelength, which is the distance covered by a single cycle, and multiply that by the frequency, which is how many cycles are completed in a second, a given amount of time. The cycles cancel out, and we're left with units of distance over time, the same as speed.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 can take its wavelength, which is the distance covered by a single cycle, and multiply that by the frequency, which is how many cycles are completed in a second, a given amount of time. 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.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 different types of waves move at different speeds. A relatable example of different waves moving at different speeds is lightning.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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 thunder comes second.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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. 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 before you hear the thunder.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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 it does in air for that exact reason. The particles in the liquid are closer together.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 it does in air for that exact reason. 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 information.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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 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, and the frequency, which is how many wave cycles complete in one second.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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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, and the frequency, which is how many wave cycles complete in one second. In this case, we have two cycles in one second for a frequency of two Hertz. Wave speed is found by multiplying wavelength and frequency, and that wave speed is affected by the type of wave and the medium through which the wave travels. Mechanical waves are waves that travel through a medium, so sound, a slinky or rope, ocean waves, and electromagnetic waves like light are special because they can travel through a vacuum.
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Wave properties Wave properties High School Physics Khan Academy.mp3
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So I have three different asteroids over here and they have different masses. And we'll talk a lot more about what mass means. But one way to think about it is how much stuff there is there. There's other ways to think about it. And so let's say that this first asteroid is twice the mass of either of these two smaller ones. And these two smaller ones have the same mass. Now we've attached the back of a rocket to each of these asteroids.
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Force, mass and acceleration Movement and forces Middle school physics Khan Academy.mp3
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