Learn about Fluids - part 1 Video

By: Guest More than a year ago

Your fluid pressure videos are really well done. I like that the science is sound and your explanations are easy to understand and follow. I am a Grade 8 Science teacher in Toronto , Canada, and I would like to use your videos to support my Fluids unit. I am going to check out your other videos. Great job! Lynn

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Learn about Fluids - part 1

Learn about Fluids - part 1 Let’s learn a little bit about fluids, and you probably have some notion of what a fluid is. But let’s talk about it in the physics science or maybe even the chemistry science depending on what context that you’re watching this video. So, fluid is anything that takes the shape of its container. So, for example, if I had a glass sphere, let’s say they were in my k or let’s say I completely fill this glass sphere with water. Let’s going to see what a zero gravity in barometer but you really don’t’ even need that. Let’s say that every cubic centimeter or cubic meter of glass sphere is filled with water. And then, let’s say that if I were to - then, let’s say it’s not a glass, let’s say it’s a rubber sphere. If I were to change the shape of that sphere but not really change the shape of the volume, and if I were to change the shape of the sphere where it look like this now. The water would just change its shape with the container, and in this case I have green water. The same is also true if I had a - if that was oxygen or if that was just some gas, it would fill the container, and in this situation, it would also fill the newly shaped container. So, a fluid in general, takes the shape of container. And, I just gave you two examples of fluids; you have liquids, and you have gasses. Those are two types of fluid. Both of those things take the shape of the container. And then, what’s the difference between a liquid and a gas then? Well, a gas is compressible, which means that I could actually decrease the volume of this container, and the gas will just become denser within the container. So, you can think of it as if I blew air into a balloon, you could squeeze that balloon a little bit. There’s air in there, I mean some point, the pressure might get high enough to pop the balloon but you can squeeze it. Well, a liquid is incompressible. And, how do I know that liquid is incompressible? Well, imagine the same balloon filled with water, completely filled of water, if you squeezed on that balloon from every sides, so let’s say that - let me pick different color, let’s say I had this balloon and it was filled of water. If you squeezed on this balloon form every side, you would not be able to change the volume of this balloon. No matte what you do, you would not be able to change the volume of this balloon. No matter how much force or pressure you put from any side on it. Well, if this was filled with gas, and magenta balloon for gas, you actually could decrease the volume by just increasing the pressure on all sides of the balloon. And you can actually squeeze it, and make the entire volume smaller. So, that’s defined a liquid and a gas. Gas is compressible and liquid is within of, and we’ll learn later that you can turn a liquid into a gas and gas into a liquid, and turn a liquid into a solid. Well, we’re in all about that later. But this is a pretty good working definition of that. So, let’s use that and I were going to actually just focus on the liquids to see if we could learn a little bit about liquid motion or maybe even motion in general. Okay, let me draw something else. So, let’s say I had a situation where - let’s say I have this weird shaped object which tends to show up in a lot of physics books, which I’ll draw it in yellow. It’s weird shaped container where it’s rout ably narrow there, and then it goes in kind of u-turns and to a much larger opening. Let’s say that the area of this opening is - let’s say that this isA1, and the area of this opening is A2, and this one is bigger. And let’s fill this thing with some liquid, which will be blue. So, that’s my liquid. Let’s fill it with some liquid, and let me see if they have this tool. There you go, look at that; I filled it with liquid so quickly. This was liquid, and it’s not just a fluid. And so, what’s the important thing about liquid is that it’s incompressible. So, let’s take what we know about force, actually about work, and see if we can come up with any rules about force and pressure with liquids itself. So, what do we know about work? Work is force times distance, or you can also kind of view this, the energy put into the system. Alright, down here. So, work is equal to force times distance. And we learned in mechanical advantage, etc. that the work-in is equal to work-out. The force times the distance that you put into a system is equal to the force times the distance you put out of it. And you might want to review the work chapters on that. But that’s just the law of conservation of energy because work-in is just the energy that you’re putting into a system, right? It’s measured in joules in a work-out as the energy that comes out of the system. And that’s just saying that no energy is just order created, it just turns into different forms. So, let’s just use this definition. The force times the distance-in is equal to force times distance-out. Force-in, although I like that, times distance-n is equal to force-out times distance-out. Alright, so let’s say that I pressed with some force on this entire surface. So, let’s say I had like the - let’s say it’s like a Piston and we’ll see if I can grow up this too much a good color for Pistons. So, let’s say I had a magenta Piston right here, and I pushed down on this magenta Piston. So, I pushed down on this with the force of F1. And let’s say I pushed a distance of D1. So, let me say it goes - that’s its initial position and say its final position. I’ll do in a color -. The hardest part of this video is picking the color. So, let’s say like after I pushed it, the Piston goes this far. So, this is the distance that I pushed at. So, this is D1. The water is here, and I pushed the water down, D1 meters, whatever, right? So, in this situation, my work-in is F1 times D1. But let me ask you a question. How much totals water did I displaced? What’s this volume? I took this entire volume and pushed it down. So, what’s the volume right there that I displaced? Well, the volume there is going to be - so, the initial of the volume that I’m displacing. Let’s all say that the volume displaced has to equal this distance, right? This is like a cylinder of liquid. So, this distance times the area of that container f that foil. And I’m assuming it’s constant at that point and then it changes after that. So, it equals area one times distance one. Well, we also know that liquid has to go some place because what do we know about liquid, is that you can’t compress it; you can't change its total volume. So, all of that volume is going to have to go some place else. So, this is where the liquid was. The liquid is going to raise some level. Let’s say it gets to this level. Let’s say it’s a new level, right? It’s going to change some distance there, and how do we know what that distance has going to be? Well, the volume that it changes here has to - if I had to go some place, you cannot say, “Well, that’s going to push on that, that’s all going to push in.” That liquid has to some place and essentially it’s going to end up. It might not be the exact same molecules but that might display some liquid here. That’s going to displace some liquid here, here, and here, and here, and all the way until the liquid up here gets displaced and gets pushed upward. So, the volume that you’re pushing down here is the same volume that goes up right here. And so, how much volume did you pushed up here? Well, this volume here is going to be the distance two times this larger area. So, we could say volume two is going to be equal to the distance two times this larger area. And we know that this liquid is incompressible. So, this volume has to be the same as this volume. So, we know that these two quantities are equal to each other. So, area one times distance one, right? This area times this distance is going to be equal to this area times this distance; area two times distance two. So, let’s see what we can do. We notice that the force-in times the distance-in is equal to the force-out times the distance-out. Let’s take this equation. I’m going to switch back to green so that we don’t lose track of things, and divide both sides by - well, let’s just rewrite it. So, let’s say I rewrote each input force - actually I’m about to run out of time, so I’ll continue this into the next video. See you soon.

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Learn about Fluids - part 1

Let’s learn a little bit about fluids, and you probably have some notion of what a fluid is. But let’s talk about it in the physics science or maybe even the chemistry science depending on what context that you’re watching this video.

So, fluid is anything that takes the shape of its container. So, for example, if I had a glass sphere, let’s say they were in my k or let’s say I completely fill this glass sphere with water. Let’s going to see what a zero gravity in barometer but you really don’t’ even need that. Let’s say that every cubic centimeter or cubic meter of glass sphere is filled with water. And then, let’s say that if I were to - then, let’s say it’s not a glass, let’s say it’s a rubber sphere. If I were to change the shape of that sphere but not really change the shape of the volume, and if I were to change the shape of the sphere where it look like this now. The water would just change its shape with the container, and in this case I have green water.

The same is also true if I had a - if that was oxygen or if that was just some gas, it would fill the container, and in this situation, it would also fill the newly shaped container. So, a fluid in general, takes the shape of container.

And, I just gave you two examples of fluids; you have liquids, and you have gasses. Those are two types of fluid. Both of those things take the shape of the container. And then, what’s the difference between a liquid and a gas then? Well, a gas is compressible, which means that I could actually decrease the volume of this container, and the gas will just become denser within the container. So, you can think of it as if I blew air into a balloon, you could squeeze that balloon a little bit. There’s air in there, I mean some point, the pressure might get high enough to pop the balloon but you can squeeze it.

Well, a liquid is incompressible. And, how do I know that liquid is incompressible? Well, imagine the same balloon filled with water, completely filled of water, if you squeezed on that balloon from every sides, so let’s say that - let me pick different color, let’s say I had this balloon and it was filled of water. If you squeezed on this balloon form every side, you would not be able to change the volume of this balloon. No matte what you do, you would not be able to change the volume of this balloon. No matter how much force or pressure you put from any side on it.

Well, if this was filled with gas, and magenta balloon for gas, you actually could decrease the volume by just increasing the pressure on all sides of the balloon. And you can actually squeeze it, and make the entire volume smaller.

So, that’s defined a liquid and a gas. Gas is compressible and liquid is within of, and we’ll learn later that you can turn a liquid into a gas and gas into a liquid, and turn a liquid into a solid. Well, we’re in all about that later. But this is a pretty good working definition of that.

So, let’s use that and I were going to actually just focus on the liquids to see if we could learn a little bit about liquid motion or maybe even motion in general. Okay, let me draw something else.

So, let’s say I had a situation where - let’s say I have this weird shaped object which tends to show up in a lot of physics books, which I’ll draw it in yellow. It’s weird shaped container where it’s rout ably narrow there, and then it goes in kind of u-turns and to a much larger opening. Let’s say that the area of this opening is - let’s say that this isA1, and the area of this opening is A2, and this one is bigger.

And let’s fill this thing with some liquid, which will be blue. So, that’s my liquid. Let’s fill it with some liquid, and let me see if they have this tool. There you go, look at that; I filled it with liquid so quickly. This was liquid, and it’s not just a fluid. And so, what’s the important thing about liquid is that it’s incompressible.

So, let’s take what we know about force, actually about work, and see if we can come up with any rules about force and pressure with liquids itself. So, what do we know about work? Work is force times distance, or you can also kind of view this, the energy put into the system. Alright, down here.

So, work is equal to force times distance. And we learned in mechanical advantage, etc. that the work-in is equal to work-out. The force times the distance that you put into a system is equal to the force times the distance you put out of it. And you might want to review the work chapters on that.

But that’s just the law of conservation of energy because work-in is just the energy that you’re putting into a system, right? It’s measured in joules in a work-out as the energy that comes out of the system. And that’s just saying that no energy is just order created, it just turns into different forms.

So, let’s just use this definition. The force times the distance-in is equal to force times distance-out. Force-in, although I like that, times distance-n is equal to force-out times distance-out. Alright, so let’s say that I pressed with some force on this entire surface. So, let’s say I had like the - let’s say it’s like a Piston and we’ll see if I can grow up this too much a good color for Pistons.

So, let’s say I had a magenta Piston right here, and I pushed down on this magenta Piston. So, I pushed down on this with the force of F1. And let’s say I pushed a distance of D1. So, let me say it goes - that’s its initial position and say its final position. I’ll do in a color -.

The hardest part of this video is picking the color. So, let’s say like after I pushed it, the Piston goes this far. So, this is the distance that I pushed at. So, this is D1. The water is here, and I pushed the water down, D1 meters, whatever, right?

So, in this situation, my work-in is F1 times D1. But let me ask you a question. How much totals water did I displaced? What’s this volume? I took this entire volume and pushed it down. So, what’s the volume right there that I displaced? Well, the volume there is going to be - so, the initial of the volume that I’m displacing. Let’s all say that the volume displaced has to equal this distance, right? This is like a cylinder of liquid. So, this distance times the area of that container f that foil. And I’m assuming it’s constant at that point and then it changes after that.

So, it equals area one times distance one. Well, we also know that liquid has to go some place because what do we know about liquid, is that you can’t compress it; you can't change its total volume. So, all of that volume is going to have to go some place else.

So, this is where the liquid was. The liquid is going to raise some level. Let’s say it gets to this level. Let’s say it’s a new level, right? It’s going to change some distance there, and how do we know what that distance has going to be? Well, the volume that it changes here has to - if I had to go some place, you cannot say, “Well, that’s going to push on that, that’s all going to push in.”

That liquid has to some place and essentially it’s going to end up. It might not be the exact same molecules but that might display some liquid here. That’s going to displace some liquid here, here, and here, and here, and all the way until the liquid up here gets displaced and gets pushed upward.

So, the volume that you’re pushing down here is the same volume that goes up right here. And so, how much volume did you pushed up here? Well, this volume here is going to be the distance two times this larger area. So, we could say volume two is going to be equal to the distance two times this larger area.

And we know that this liquid is incompressible. So, this volume has to be the same as this volume. So, we know that these two quantities are equal to each other. So, area one times distance one, right? This area times this distance is going to be equal to this area times this distance; area two times distance two.

So, let’s see what we can do. We notice that the force-in times the distance-in is equal to the force-out times the distance-out. Let’s take this equation. I’m going to switch back to green so that we don’t lose track of things, and divide both sides by - well, let’s just rewrite it. So, let’s say I rewrote each input force - actually I’m about to run out of time, so I’ll continue this into the next video. See you soon.

Transcription by: Scribe4you Transcription Services