Wonder World Of Science: Can I Sit On A Cloud? (1987)

I wonder. I wonder What do you wonder, Wonder Cat? I wonder. Can I sit on a cloud? Can you sit on a cloud? Well, you can answer that question if you know what clouds are made of. What are clouds made of? If you're curious enough, you can find out. I'd need an airplane for that. Clouds are too high. Clouds are high, all right, but sometimes mountains are even higher. Let's go to the mountains. Hey, that's a cloud. If we could get there, I could find out what it's made of. And then I could find out if I can sit on it. Here's your cloud. And it's like a fog. Right. A fog is just a cloud that's close to the ground. And the fog feels wet, doesn't it? So, the cloud, or the fog, must be made of water. Yes, that's right. Well, if a cloud is just like a fog, then I guess I can't sit on it. But if a cloud is made of water, like a lake is, could I float on it? Boats float on water, so do people. So can I? So, can I float on a cloud? Well, the water that's in a lake is different from the water that's in a cloud. Water in a lake can spray up into the air and separate into drops that fall back into the lake. Water in a cloud is always in drops, but not nearly as big as the drops in the spray. Water drops in a cloud are so tiny and weigh so little that the moving air can hold them up. They seem to float in the air. Does that mean that I can't float in a cloud? That's right. But I wonder, where does cloud water come from? Most cloud water comes from the oceans. It does? How? Well, look on the rocks over there. At those puddles that the waves made? Yes. What do you think will happen if no more ocean water falls into them? Well, I guess after a while they'll dry up, sort of disappear. That's right. If we could speed up what happens, it would look like this. Where does the water go? It goes into the air. The water changes into invisible water vapor. It evaporates. But not just the water from the puddles evaporates into the air. Water from the ocean and lakes and rivers and everything that's wet does this all the time. Including me? That's right. You'll get dry because the water will evaporate from you. The warm sun helps to make the water evaporate. I think I understand. The warm sun helps water evaporate into the air. It changes into invisible water vapor. Very good. But how does that water vapor change back to water and get into the clouds? Well, water doesn't get into the clouds. The clouds are water. Then how does the water vapor we can't see become a cloud we can see? Why, you've made it happen many times. I have? When? On cold days with the warm moist air you breathe out of your body. Hey, I made a cloud. When the water vapor in your warm breath is cooled, some of it changes into a cloud of tiny water droplets. So that's what must happen with clouds. That's right. You see, high up where the clouds are, the air is cooler than it is near the ground. When moist air gets cool enough, the invisible water vapor in it changes to tiny droplets that make clouds. But I wonder, why are there different kinds of clouds? Some clouds are fluffy and white. And some are dark gray, almost black. Well, it all has to do with those tiny droplets that clouds are made of. The clouds that first form when the droplets come out of the air are white clouds, like the clouds your breath makes. The white clouds are fair weather clouds. But if more and more of the tiny water drops come out of the air, and the cloud gets bigger, the drops bump together and get bigger, too. Now the clouds get darker and darker. These are rain clouds. And finally, when the drops are much bigger and much heavier than they were when the cloud first formed, the drops of water are heavy enough to fall to the ground. And do you know what you get? Rain. Exactly right. But I was just wondering, if a cloud is water, how can it snow? I know snow is frozen water, but how do we get snowflakes? Well, if the temperature of the air is below freezing, the water vapor doesn't change into tiny water droplets. Instead, the water vapor changes into tiny crystals of ice. These ice crystals make snow clouds. The crystals are the beginnings of snowflakes. They get bigger in the cloud, and after a while, if they get heavy enough, they gently fall to the ground. But if the air that they fall through is warm enough, the snowflakes may melt on the way down and change to rain. Rain and snow are just different forms of water falling from the clouds. Then why are there still clouds after it rains? For the same reason there are clouds before it rains. The water drops in the clouds aren't heavy enough to fall. But clouds are changing all the time, whether it rains or not. And if we could speed up how they change, it would look like this. Their shapes change. The wind blows them from one place to another place. They bump together and break apart. The clouds are always changing. But what they are doesn't change. I know they're all made of some kind of water, and I can't sit on a cloud. But I can sit on what used to be a cloud when it's frozen and on the ground and made into a snowman like this. But not for very long. It's cold.