Many people think that clouds form due to the process of the water cycle phase, evaporation. It is true that without evaporation, clouds would not exist. Evaporation is the process of liquid water turning into gaseous water, or water vapor. Without evaporation as a part of the water cycle, water would only cycle from liquid to solid, and would never make it off the ground.
Liquid water is relatively “sticky”, the molecules when water is in a liquid state are attracted to each other creating a lattice of water molecules. Think about how water can “stick” to the sides of a glass, your mirror during a shower, or itself when you’ve poured a glass of it too high, and it domes up above the edge of the glass (try it!).
When liquid water molecules have enough energy, some of them break away from the liquid water lattice. A single water molecule is less dense than our typical air molecules (nitrogen and oxygen) so it rises up through the air. That’s usually where water vapor hangs out, amid our air molecules. But we don’t see it.
Water molecules floating around alone are far too small to see. Even so, a common misconception exists that evaporation, liquid water becoming water vapor, creates clouds. But we can see clouds! And we can see liquid water. So at some point, the water vapor must turn back to liquid water, otherwise known as the process of condensation.
Remember that it takes water molecules with energy to break away to form water vapor, so the opposite needs to happen to water vapor molecules to slow down enough to allow their natural attraction to take hold. The temperatures further from the surface of Earth are colder due to less pressure (“thinner” air), so as water vapor rises in the air, it cools, or the molecules lose energy and slow down. In addition to sticking to each other, water molecules tend to need a surface to form onto. Our atmosphere is full of microscopic dust which provides a perfect surface for microscopic water molecules to cling to as they lose energy. The lattice formed between the clinging water and dust is our cloud!
So in a typical graphic that appears in many student textbooks, we can see the cause and effect that creates this cycle of cloud formation:
In a recent workshop, fifth grade teachers from Franklinville, Randolph Academy, West Valley, and Genesee Valley practiced an activity they do with their students in the Models of the Earth Advancing STEM Kit.
This activity helps students understand the conditions needed for a cloud to form. There are different scenarios represented by four combinations of water and air: (1) cold water/cold air; (2) cold water/warm air; (3) warm water/cold air; and (4) warm water/warm air. You can see in the picture that water droplets have formed on the top of one of the cups enclosing the land. What do you think is the combination that created this “cloud”? This activity goes along great with one of the third grade NYS Required Science Investigations: Cloud in a Bottle.
Another great activity to do with kids or by yourself is Cloud BINGO. This fun activity can help develop keen observation skills and practice prediction. Record the date and time when you see a type of cloud and record the weather going on at the time you see this cloud. You can make this a competition if you set a time frame, say three weeks, and whoever has seen the most clouds, wins!
Follow-up questions to a few weeks of cloud observations might be: What type of weather would you expect with thin, wispy clouds? What type of weather would you expect with thick, fluffy clouds? What type of weather would you expect with dark clouds? What did you find were the most common types of clouds? The least common? Are there any clouds that indicate bad weather or good weather is on the way? Are there any clouds that signify a storm is now over? Did you discover any other types of patterns?
By: Kelli Grabowski, CA BOCES Learning Resources
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