Name: 水 - 液体オーサム。クラッシュコース生物学 #2 (Water - Liquid Awesome: Crash Course Biology #2)
Uploaded: 2021-01-14T04:20:39.000Z
Duration: 11 min 17 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

Here at Crash Course HQ we like to start out each day with a nice healthy dose of water

It's the only substance on all of our planet earth that occurs naturally in solid, liquid,

And to celebrate this magical bond between two hydrogen atoms and one oxygen atom

here, today, we are going to be celebrating the wonderful

But we're going to do it slightly more clothed.

When we left of here at the Biology Crash Course, we were talking about life

and the rather important fact that all life as we know it is dependent upon there being

Scientists and astronomers are always looking out into the universe trying to figure out

because that is kind of the most important question that we have right now.

They're always getting really excited when they find water someplace

And this is one reason why I am so many other people geeked out so hard last December when

Mars' seven-year-old rover, Opportunity, found a 20-inch long vein of gypsum that was almost

certainly deposited by long-term liquid water on the surface of mars.

And this was probably billions of years ago, and so it's going to be hard to tell

whether or not the water that was there resulted in some life.

But maybe we CAN figure that out and that would be REALLY exciting!

But why?! Wy do we think that water is necessary for life?

Why does water on other planets get us so freaking excited?

So let's start out by investigating some of the amazing properties of water.

In order to do that we're going to have to start out with THIS

The world's most popular molecule -- or at least the world's most memorized molecule.

Two hydrogens, one oxygen. The hydrogens each sharing an electron with oxygen in what we

So as you can see, I've drawn my water molecule in a particular way

and this is actually the way that it appears.

It is V-shaped. Because this big old oxygen atom is a little bit more greedy for electrons

it has a slight negative charge whereas this area here with the hydrogen atoms has a slight

Thanks to this polarity, all water molecules are attracted to one another -- so much so

they actually stick together, and these are called hydrogen bonds. We talked about them

Essentially what happens is that the positive pole around those hydrogen atoms bonds to

the negative pole around the oxygen atoms of a DIFFERENT water molecule.

Seriously though, I cannot overstate the importance of this hydrogen bond.

So when your teacher asks you, "What's important about water?"

Start out with the hydrogen bonds and you should put it in all caps and maybe some sparkles

One of the cool properties that results from these hydrogen bonds is a high cohesion for

water, which results in high surface tension. Cohesion is the attraction between two like

things, like attraction between one molecule of water and another molecule of water.

Water has the highest cohesion of any non-metallic liquid, and you can see this if you put some

water on some wax paper or some Teflon or something where the water beads up.

Some leaves of plants do it really well. It's quite cool.

Since water adheres weakly to the wax paper or to the plant, but strongly to itself, the

water molecules are holding those droplets together in a configuration that creates the

It's this high surface tension that allows some bugs and I think one lizard and also

The cohesive force of water does have its limits of course. There are other substances

that water quite likes to stick to. Take glass for example.

This is called adhesions and the water is spreading out instead of beading up because

the adhesive forces between the water and the glass are stronger than the cohesive forces

of the individual water molecules in the bead of water.

Adhesion is attraction between two different substances. In this case the water molecules

These properties lead to one of my favorite things about water: the fact that it can defy

That really cool thing that just happened is called capillary action, and explaining

it can be easily done with what we now know about cohesion and adhesion.

Thanks to adhesion, the water molecules are attracted to the molecules in the straw. But

as the water molecules adhere to the straw, other molecules are drawn in by cohesion,

following those fellow water molecules. Thank you, cohesion! The surface tension created

here causes the water to climb up the straw. And it will continue to climb until eventually

gravity pulling down on the weight of the water in the straw overpowers the surface tension.

The fact that water is a polar molecule also makes it really good at dissolving things,

Scratch that. Water isn't a GOOD solvent, it's an AMAZING solvent!

There are more substances that can be dissolved in water than in any other liquid on Earth.

Yes, that includes the strongest acid that we have ever created. These substances that

dissolve in water -- sugar or salt being ones that we're familiar with -- are called

hydrophilic, and they are hydrophilic because they are polar, and their polarity is stronger

When you get one of these polar substances in water, it's strong enough that it breaks

all the little cohesive forces, all those little hydrogen bonds, and instead of hydrogen

bonding to each other the water will hydrogen bond around these polar substances.

Table salt is ionic, and right now it's being separated into ions as the poles of

But what happens when there is a molecule that cannot break the cohesive forces of water?

It can't penetrate, and come into it. [Seriously...?]

Basically, what happens when that substance can't overcome the strong cohesive forces

That's when we get what we call a hydrophobic substance, or something that is fearful of

water. These molecules lack charged poles, they are non-polar and are not dissolving

in water because essentially they're being pushed out of the water

Water: we may call it the universal solvent, but that does not mean that it dissolves everything.

There've been a lot of eccentric scientists throughout history, but all this talk about

water got me thinking about perhaps the most eccentric of the eccentrics -- a man named