Name: How To Make a Self-Starting Siphon
Uploaded: 2020-04-13T17:51:56.000Z
Duration: 13 min 24 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Ding dong Michael here today we're gonna talk about this a thing that you could make it home.

I'm gonna fill this glass with water that I've dyed blue.

So it's easier to see all the way up to the very top of the glass.

Now watch what happens when I place this tube in the glass.

Water flows out, and it keeps flowing out.

What's pushing the water out of the glass?

I first learned about these from the curiosity show, and I am incredibly grateful because I mean, they're a blast.

It's almost like magic, but it's not magic.

It has everything to do with shape of the tube and physics.

Let's keep watching because it won't run forever.

Eventually the flow will stop, and that will happen when the water level in the glass is that the same height as the exit point of the straw?

The flow will get weaker and weaker as we approach that point.

Eventually it'll just turn into a few drops and then it will stop and the system will be in.

At this point, the forces acting on the fluid cancel each other out and the fluid stops moving.

Well, for a siphon like this, the most relevant forces are wait forces.

Every single molecule of water and air in this system is being squeezed by the weight of everything above it.

The lower down a molecule is, the more stuff there is above it, and therefore the larger weight weighs down on it.

So it's under greater pressure now because water and air can flow.

The result of this pressure isn't just a tendency to move down when possible.

Water and air molecules can slip by each other.

And so when under pressure, they're ready to move in whatever direction they can think about an air molecule right here by the exit of the straw, it is being squeezed by the weight of air above it.

And if that straw was suddenly evacuated of water and air, you better believe that under pressure, those molecules of air outside would rush inside.

All right, so now that we're thinking about pressure, let's look at a picture.

Here is a diagram of what we have been looking at, a container filled with water and a tube that is also filled with water.

The exit of the tube is at the same height as the liquid in the container, and nothing is flowing.

Well, let's take a look at the pressures at work.

First of all, it's important to note that pressure depends on depth, and that's really it.

I mean, it also depends, of course, on acceleration and gravity and the density of the fluid that urine.

But those don't really change much over these small distances.

So here at the entrance, where is the entrance?

Well, the entrance is deep in the container.

Well, it's this distance deep, and I'm gonna call this H one perfect.

Let's talk about some other depth that exists.

The entrance is also in much deeper water in the tube.

And now I'm gonna call this half the outside half in this half the inside half, So there's a lot.

The water goes up a lot higher here in the tube.

Well, from the surface of the water in the container down to the entrance.

All right, same depth, but the water goes up higher in the tube.

So H two plus H one equals the total depth on the inside of the tube.

This is the distance from the top of the tube to the exit.

Now let's talk about the pressures created here.

We've got a pressure proportional to H one that is coming from the water in the container, and that's gonna cause water to go into the straw, if possible.

But we also have a column of Water H one tall inside the straw that's creating a pressure in the opposite direction.

Um, let's not forget about air when it comes to canceling out.

By the way, there's also a Rh pressure, right air pressure pushing on the water in the container, and if this straw was empty, that would that would cause the water to go into the straw.

There's also Aaron contact with the exit and that air pressure is equal to this air pressure.

So they also cancel out all we're left with R H two and H three, the depth of water above the water in the container on both the inside and the outside of the tube.

If H two is equal to H three, that means we have the same pressure out of the straw into the container, as we do out of the straw into the environment, and so nothing will move.

However, if I pour more water into the container and say, raise the level of water in it up to here.

Now there is a greater pressure out of the container because H two has become much smaller.

H two is now only this large, and if H two is smaller than a TSH three, if the depth of water on the inside above the containers level is smaller than the depth of water on the outside, there's more pressure here moving out, and so the water will flow out until the water level in the container has dropped back down to the same level as the exit, at which point we'll be back in equilibrium.

There will be this situation H two and H three equal depths on the inside and the outside, and the water will stop moving.

Let's see this in real life, water will flow in the direction of the side of the siphon that has the deepest amount of water in it that isn't already underwater.

Right now, those depths are equal, so water isn't flowing.

But if I add some more water to the glass, the water level in the glass will go up, and the depth of the water in the siphon that isn't also underwater will get smaller relative to the depth outside, so the water will flow to the outside.

This will continue until once again the water level in the glass is equal in height to the exit of the strong.

Now let's say you don't already have a straw that's full of liquid.

Well, there's a couple of ways to do that.

One way is to kind of feel like this should finish.

Subtitles ListPlay Video

How To Make a Self-Starting Siphon

eventually

force

squeeze

pressure