What does it do?

Well, take a look.

I have here a glass.

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.

Just like that.

Perfect.

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

Pretty cool, right?

Water flows out, and it keeps flowing out.

But how is this happening?

I mean, I just put a tube in the glass.

The tube has no moving parts, no pump.

What's pushing the water out of the glass?

Well, this isn't just a two, you know.

It is a self starting siphon.

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.

Now to see how it works.

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.

Well, Marie equilibrium.

Perfect.

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

But what are the forces?

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.

Oh, no.

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.

against all the molecules below 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.

Right.

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.

Why?

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.

It's the depth that matters.

Not the volume of water, just the depth.

So here at the entrance, where is the entrance?

Well, the entrance is deep in the container.

And how deep?

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

Now before we get too far.

Let's talk about some other depth that exists.

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

Let's divide the tube in half.

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

There's a lot more water.

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

So what is this depth?

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

This is also a tch one.

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

There's also this extra depth.

I'll call this H two.

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

Over here on the outside.

How deep is the water at the exit?

Well, it is, Let's say, H three deep.

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.

So they both cancel out.

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.

But there's also a route here.

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.

So this is now all water will.

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.

Watch this.

It's regulating itself.

It's really beautiful.

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.

How do you get to this point?

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

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

It's just doing such a good job.

Yeah, thank you.

All right, So let's say your straw isn't already filled with liquid.

How do you get some Seif in action going?

Well, let's fill this up to the brim.

That makes our job a lot easier because, remember, we only need the water on the outside of the siphon to go below the water level in the glass.

So the higher that level in the glasses, the less down we're gonna need the water to have gone to get the siphon to happen.

Now, if I put this empty straw in the glass, not much will happen.

But I need the water level on the outside to get below the water level in the glass, and I could do that by just like sucking on the straw like that.

Perfect.

Now it's working, but let's say you want to siphon a liquid that you don't want in your mouth.

Well, there are a number of different options available to you all kinds of devices to draw the liquid through the siphon.

This is also a really fun thing to do with a straw.

Cover one end of the straw and place it in the glass.

Because you're covering one end, the air won't be able to escape when you put it in, so the air inside the strong will get compressed.

It's pressure will be greater, and it will push down on the water in the straw, more so than atmospheric pressure does.

When you then release your finger, the compressed air inside will escape and the water in the straw will rise up to the level of that It is in the glass.

However, it won't stop there because while the water is being pushed up by pressure, well, what is pressure right?

It's force its force per area so that force accelerates the water.

By the time the water reaches the level that it would normally stay at an equilibrium.

It still has velocity.

It's gonna be slowing down.

But if I do this just right, it won't slow down or get reversed until it's too late.

And the water's already passed over the bend and fallen down the other side, below the water level in the glass and see if I can do this.

I can use my thumb to cover the straw.

Gonna go in.

And when I release my thumb, there you go.

The water is flowing out and nothing had to get in my mouth, and that's pretty cool.

But what about this self working siphon?

How does it work?

Because I don't even have to cover it over with my thumb.

Where is my I found it.

So, yeah, how does a self starting siphon work?

I don't need to use my finger or suck on it to get it started.

It just well, true to its name is self starting.

Well, to see how this works, let's go back to the overhead camera.

Here's a cardboard model of the shape of our self starting siphon.

I'm gonna use this because this is kind of wet.

All right, So what happens when I put the self starting siphoned into a full glass of water.

Well, at first, the siphon is full of air.

As it goes down into the glass, the water in the glass enters the straw and pushes out the air.

But if I put this in really quickly, look what happens.

Well, there's enough pressure here for the water to get pushed all the way up to the top.

But that can't happen because of the bend in the strong.

So the water reaches this bend and it's still under pressure.

There's still a force acting on it, so it continues to be accelerated.

But now it's going down.

Russo is also being accelerated by gravity, so it's velocity gets larger and larger and larger.

It turns that bend and it comes all the way up here.

Once the water in the straw has reached this level, it will not be accelerating up anymore.

However, after all of this, it may have reached, we hope, if I put the straw in fast enough, a velocity sufficient to continue on around this third bend before being stopped and reversed until it is low enough, maybe, like say here that it's below the water level in the container.

When that happens, it will continue flowing.

And we've got ourselves a self started siphon.

To make your own self starting siphon, you will need a full glass of water, three bendy straws and some scissors.

Now, one of these straws will be our middle bend, and we're going to use it to ensure that one hump is higher than the other.

I'm gonna do that by cutting the straw a bit shorter on one side of the bend.

That should be about enough.

Perfect.

Now, as you can see, we're going to be able to join the straws together to make an M shape where one side is higher than the other to join them.

I like to cut the straw at a bit of a diagonal like that.

So I get a nice sharp point in a gradual widening.

That way I can push them together, let the plastic to form, and they come together.

Hopefully with a really nice air tight and watertight seal.

Is that good?

All right, Well, the best way to check is to cover one end with your finger and suck on the other end.

If it feels good, then it should hold the vacuum.

I'm happy with that.

Very good.

All right, Now let's join up the other side again.

I'm going to cut at a diagonal just like that, and then I'm gonna push them together.

If you're having trouble with your seals, you can always put some tape around the joint, and that might be all you need to do.

But it's extremely important that they be air and water tight.

Let's see how well I've done cover one end suck.

Yeah.

See that?

That's good guy.

Not good.

Feel all right?

We're not quite done because I need to shorten one end.

I want the lower hump to be submerged in the water, and right now, the straws is a bit too long.

So when the higher hump is at the edge of the glass, I think I'll need it to be maybe that short to be safe, to make sure it's gonna fit in the glass.

And let's make sure the seal is still good.

Okay.

All right.

I think we're ready.

I think we're ready to test our homemade self starting siphon in 321 Hey, look at that.