Through this activity children will realize that water naturally changes its structure and understand how rain and clouds are formed. They will realize that though the amount of water in nature does not change, its structure does (liquid, solid, gas) and understand that if there is no evaporation of water from an area located below or beside, there will be no rain.
- a cup of warm water
- transparent zipper bag
- marker pens
The bag will be a symbol of a piece of nature. Let’s assume this is our preschool garden. Paint the soil at the bottom of the bag, and then a flower meadow and a tree growing from the soil. Paint a small pond in the middle. Let’s draw the sun and cumulus (fluffy) clouds above. Now pour the right amount of water into the bag, so that its bottom is filled with water up to the level of the ground, which you painted before. This will make the lake look like it’s filled with water. The flowers will be growing above the ground water level. If by mistake we pour too much water, it will look like the flowers are growing under the water or in the water. In that case, we should pour out the excess of water. Let’s do it before starting the experiment. When the right water level is reached, close the bag tightly and fix it with tape to the window. We will talk about changes throughout the day. We should see slight differences in water levels. At the end of the day we shall see, what happens when the sun warms the water in a pond and at the flower meadow. During free play, observe the bag for changes, which we will discuss at the end of the day.
I OBSERVATION: The appearance of steam in the bag
EXPLANATION: When heated by the sun water begins to evaporate. Water changes its state from liquid to gas. How does it happen? We can say that warm molecules are getting more and more mobile and pulling away from each other. At some point they are so light that they can rise into the sky.
II OBSERVATION: Condensation of water vapor
EXPLANATION: When moving through the air, water vapor cools down quickly. When it reaches its dew point (i.e., temperature low enough to condense), it settles quite quickly on any available surface in the form of droplets. In our case the steam touched the surface of the bag and started condensing there. Such a phenomenon is very often observed in nature. When in the morning we go out into the garden or park, we can feel the dew on our feet. Why is that? At night, water vapor, that is in the air, touches the cool leaves and settles on them. In the morning, with bare foot we can feel the water vapor on leaves.
Would you like another example, which illustrates the settlement of water vapor? On a sultry and steamy day, our body quickly gets damp. Not only because “water evaporates from us”, but mainly because water droplets from humid air settle on our skin.
One more example. When we want to clean the glasses and we exhale on the lenses, a small part of the water vapor we exhale settles on the cold lenses, making cleaning easier.
III OBSERVATION: The droplets run down the surface of the bag
EXPLANATION: You can see how the droplets are running down the bag looking like raindrops. Do you know that what happens in the bag is very much like formation of clouds and rain? Water that evaporates from the soil, grass or forest rises into the atmosphere. Water vapor increases the humidity in the air. At some point, as altitude increases, the water vapor cools down. Just as with dew or glasses which we have just spoken about, the water vapor is ready to condense. High in the sky, a tiny droplet gets formed. When such a droplet meets dust floating in the air, it will settle on it. All the droplets do it. There are more and more of them, and they get bigger and bigger. Finally, many droplets form a cloud. At some point, when the water in the cloud becomes heavy enough, it falls. We say rain is falling from the sky. Some people don’t know where it comes from. However, we already know that these are the same water droplets that were in our garden or pond a moment earlier, they just evaporated.
We saw a similar phenomenon in our bag. The sun warmed the water in the bag. The molecules broke off, turning into water vapor. The steam circulated in the bag until it finally touched the top of the bag. It turned back to water. When a few drops meet, they are heavy enough to run down the side of the bag. They come back to our flower meadow and to the pond from which they will evaporate again after a while. And so, on and on and on.
The post was created as part of the project “I love Warsaw – I’m catching rainwater” financed by the Veolia Foundation.