Name: The water cycle | Ecology | Khan Academy
Uploaded: 2017-04-01T00:01:24.000Z
Duration: 8 min 14 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...

about the water cycle, which we're all familiar with.

In fact, we're all part of the water cycle,

So we could start with the surface of the ocean here,

there's going to be water evaporating off of that surface.

Water molecules that were in their liquid state,

liquid state, they just have enough energy to bounce away

And water in a gaseous state we call vapor, water vapor.

And so that water vapor, it is going to rise,

likely with the air that has been heated on the surface,

due to the sun, and there's other more complex dynamics

at play, but as it rises, and as the overall temperature

cools, that water vapor will condense into little droplets.

It'll condense around little, tiny air particles,

little particles of dust that you can't even see

with your eye, and that's what forms clouds.

So this is little droplets, so the water's actually back

to the liquid form, they're not individual water molecules

anymore, they're now able to interact with each other,

and they're condensing around these little,

microscopic dust particles to form these water droplets.

And if it's cold enough, they might also form

small ice crystals, and that's what clouds are.

And we see here, they're talking about transportation,

you can have these clouds, we obviously, if you look outside

and you see clouds, those clouds are moving with the wind.

And so they could be moving all of those droplets

And when those droplets get heavy enough,

they will precipitate, they will precipitate down.

Now they could precipitate back into where we started,

Or ice, but then eventually things might warm up,

or they might not warm up, but if they do warm up,

so let's say it's not cold enough for it to be snow,

Well, most of that water is actually going to

We look around us and we see these rivers and lakes,

and we say wow, there's a lot of water there.

But it turns out, there's actually a lot more water

inside the ground and obviously, in the ocean.

And we'll talk about that in a little bit.

But some of it also ends up in these lakes

and these lakes are usually in a situation where

the ground is either already saturated with water,

and similarly, rivers are formed by runoff,

it's snow melt run-off can famously form rivers.

And in general, if you see a creek or a river

near your house, especially when it rains it fills up,

that's a good indication that the ground water's

already saturated and so things are running off

And so that in general is the water cycle.

You have evaporation, it condenses into clouds,

it eventually precipitates, and it keeps going,

Now of course, there's others actors at play.

Plants will take up water from the upper soil,

And it will use that water to transport nutrients

the photosynthesis process that we've studied

And a lot of that water gets transpired out.

So once again, this is transpiration, essentially,

That's going straight from the solid form of water, ice,

into the gas form of water, or water vapor.

And this will happen in situations where it's cold

So instead of going into the liquid state,

right then the water molecules start just leaving

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The water cycle | Ecology | Khan Academy

stuff

obvious

eventually

associate