At some point in our lives, we’ve all sprawled on our backs and gazed in wonder at fluffy, drifting clouds.
Technically, clouds are a massive collection of tiny ice crystals or water droplets — so tiny, they float way up in the air. But for your students, clouds are more than just dust and water. They’re mysterious, puffy objects that wander through the sky and constantly change into endless, wonderful shapes.
It can be challenging to communicate the facts about clouds without losing the wonder of them as well. Let’s take a look at the science behind clouds and their formation, along with some fun experiments to capture your students’ imagination.
How Clouds Form
Despite their cotton-like appearance, clouds are made from billions of tiny droplets of water.
All air holds water. Close to the ground, it’s just in the form of an invisible gas — water vapor. This warm air rises and gets colder the higher it floats. High in the sky, the air pressure drops and the once-warm air expands as it gets colder. Cold air isn’t able to hold as much water as hot air, so as the warm air cools, some of this water vapor condenses around very small pieces of dust or other pollutants. This water forms a tiny droplet around each particle. If the air is cold enough, the water freezes into little ice crystals. Billions of these droplets or crystals gather together to form a cloud.
What Is Condensation?
Condensation is a part of the water cycle and is an essential part of cloud formation. The change of water from a gas to liquid form, condensation happens by a shift in air pressure and temperature.
After a shower, your bathroom mirror “fogs up.” If you wipe the surface of the glass, small drops of water collect on your hand and the mirror. This condensation occurred because the hot air from the shower cooled dramatically when it interacted with the cold surface of the glass. The rapidly cooling air couldn’t hold as much water as warm air, and the vapor reverted to its liquid form.
In the atmosphere, warm air cools as it rises, and water vapor condenses around tiny pieces of matter. These drops or crystals of condensed water form clouds.
Other Common Questions About Clouds
Your students’ questions won’t stop at, “How do clouds form?” Clouds have dozens of fascinating qualities that naturally engage a child’s curiosity, so be prepared to answer a barrage of cloud-related questions. Here are three of the most common cloud questions.
1. Why Do Clouds Float?
How do these giant, fluffy objects stay high in the sky? Why don’t they sink down to the ground?
Because clouds come from warm air, they have a higher temperature than the air around them. As long as the cloud is warmer than the atmosphere around it, it will float suspended in the sky.
2. Why Are Clouds White?
Light travels through the air in waves with different lengths, and each color we see has a unique wavelength. The ice crystals or drops of water inside clouds are big enough to scatter the light of all seven colors almost equally, which makes them look white.
But we all know that clouds sometimes get gray and ominous. This is because the light that hits a cloud gets reflected back towards the sun, so the bottom of the cloud — the part we see — looks gray. In rain clouds, the water droplets are larger and scatter even more light, meaning less light makes it out the bottom of the cloud. Because they are denser than normal clouds, rain clouds are consequently darker.
3. How Do Clouds Move?
Clouds are tossed around by the winds high in the atmosphere. The highest cirrus clouds are carried by the zooming jet stream, which makes them move incredibly fast — sometimes over 100 miles per hour. Thunderstorm clouds generally move fast, too, but not that fast. Typically, a storm blows through an area between 30 and 40 miles per hour.
The Different Types of Clouds
Clouds come in a wide range of shapes and sizes, but every type is highly specialized — just by looking at a cloud, you can tell how high it’s floating and can even predict the weather.
Clouds are broadly categorized into three groups based on height — cirrus, alto and stratus — although there are a few other kinds as well. We’ll break down the categories and examine the different clouds found within each.
1. Cirrus Clouds
Cirrus clouds are the highest clouds, forming above 18,000 feet in the atmosphere. There are three types of cirrus clouds: cirrus, cirrostratus and cirrocumulus.
- Cirrus: These common high clouds give this category its name. Made up of ice crystals, cirrus clouds look thin and wispy and high winds blow them into long streams. Usually white, cirrus clouds predict pleasant weather, but watch them closely — they often indicate that the weather is going to change in the next 24 hours.
- Cirrostratus: Thin and sheetlike, cirrostratus clouds often fill the whole sky. A bank of cirrostratus clouds is very thin, and sometimes you can see the moon or sun shining through them. Typically, if you notice cirrostratus clouds, expect a storm in the next 12 to 24 hours.
- Cirrocumulus: These small, round clouds form long rows high in the sky. Look for cirrocumulus clouds during the cold winter months — if you see them in your sky, you can expect cold but fair weather. However, in tropical areas, cirrocumulus clouds can indicate the approach of a hurricane.
2. Alto Clouds
The “in-between” clouds, alto clouds hover anywhere between 6,500 and 18,000 feet in the air. There are only two types of alto clouds to remember — altostratus and altocumulus.
- Altostratus: These blue-to-gray clouds typically cover the whole sky, and they are formed from both drops of water and ice crystals. In thinner areas, you might barely see the sun through them. Grab your umbrella if your sky is filled with altostratus — they often form before storms with continuously falling snow or rain.
- Altocumulus: Gray and puffy, altocumulus form around water droplets instead of ice. Usually, altocumulus clouds huddle together in groups. Watch out if you see them on a hot and humid morning — thunderstorms will probably come in the late afternoon.
3. Stratus Clouds
These are the lowest-hanging types of clouds and form anywhere up to 6,500 feet. Three types of clouds are categorized as stratus clouds — stratus, stratocumulus and nimbostratus.
- Stratus: This category is named after these gray and uniform clouds. Stratus clouds will often fill the whole sky, and they almost look like fog that hovers just above the ground. Stratus clouds often produce a light drizzle or mist.
- Stratocumulus: Puffy, low to the ground and very gray, stratocumulus clouds gather in lines. Hints of blue sky peek out between the rows. Although stratocumulus clouds rarely produce precipitation, they can easily grow into rainy nimbostratus clouds.
- Nimbostratus: These clouds are a dark, broody gray, and are often associated with continuous precipitation, either snow or rain. You won’t get storms out of nimbostratus clouds, though — just light or moderate precipitation.
4. Clouds That Grow Vertically
Both cumulus and cumulonimbus clouds grow vertically, towering high into the sky. But they have a few important distinctions:
- Cumulus: These are the dreamy shape-shifting clouds, the ones perfect for lying on your back and trying to decide what they look like. Cumulus clouds are fluffy and white, resembling suspended pieces of cotton candy. Known as “fair-weather clouds,” cumulus clouds have a flat base and rounded tops, and they often float along only 3,300 feet above the ground.
- Cumulonimbus: Giant and ominous, we all know cumulonimbus clouds as the clouds in thunderstorms. Often, high winds flatten out the tops of cumulonimbus clouds, giving these multi-layered clouds a distinct anvil appearance. With cumulonimbus clouds, expect heavy snow, rain, lightning, hail and sometimes tornadoes. These giants can grow up to 50,000 feet tall.
5. Other Types of Clouds
Some clouds don’t fit into the normal “cloud” categories. Here are a few of the most common:
- Mammatus: These are the low hanging bumps that hang below cumulonimbus clouds. If you see a massive cumulonimbus with mammatus clouds, you can expect severe weather.
- Lenticular: You’ll only see lovely lenticular clouds if you live around mountains. Because of both their extreme heights and the low valleys in between them, mountains redirect winds in wave patterns. These waving winds create soft and smooth lenticular clouds, which look like frisbee discs or even flying saucers.
- Contrail: Who hasn’t looked in wonder at the long slashes of clouds left in the wake of airplanes? These short-lived clouds are called contrails and form from the condensation expelled by jet airplanes. The hot and humid exhaust of a plane reacts with the cold, low-pressure air around it, creating strings of clouds that stitch across the sky.
- Fractus: These are the small, ragged fragments of clouds that have been torn from larger clouds. Fractus clouds don’t have a clearly defined base, change constantly, and are usually indicative of strong winds.
- Fog: When we walk through fog, we experience what it’s like to walk through a cloud. This “cloud-on-the-ground” typically forms when warm southerly winds bring a wave of humid air into an area. The warm air blows over a much colder soil or snow, and it begins to cool from below. If the air can’t absorb any more moisture, the water will condense and create a cloud.
For an engaging look at how clouds form, try one of these two easy experiments — you’re sure to keep your students’ attention. Using experiments is a great way to easily communicate cloud facts to children, and to keep them focused throughout the lesson.
1. Cloud in a Bottle Experiment
You don’t need many materials to create your very own cloud. Try this experiment to give your students a hands-on demonstration of the steps and ingredients required for clouds to form.
Here are the tools you need to collect:
- 2-liter clear plastic bottle
- Warm water
Follow these step-by-step instructions to create a cloud in your classroom.
- Pour warm water into the clear plastic bottle until it’s roughly one-third full. Twist on the cap.
- Squeeze the bottle tightly around the middle and then release. Have your students note that nothing happens — you still need another ingredient to make a cloud. Note — if the inside of the bottle is obscured by condensation, gently shake the bottle to let the water wash it away.
- Carefully, light a match and take the cap off of the bottle. Hold the lit match over the opening.
- Quickly, drop the match into the bottle and twist the cap back on.
- Once again, slowly squeeze and release the bottle. A cloud will appear when you let go and vanish when you squeeze.
There are three ingredients to cloud formation — water vapor, dust or other particles and a drop in air pressure. The warm water adds water vapor to the air trapped inside the bottle as it evaporates. But if you squeeze and release the bottle at this point, no cloud forms — the air doesn’t yet have any debris particles.
Once you drop in the match, the smoke gives the water vapor something to condense around. Now, when you squeeze and release the bottle, a cloud forms. The final requirement for clouds is a drop in air pressure. When you squeeze the bottle, you dramatically increase the air pressure, and it drops as you release. Viola — a cloud!
2. Cloud in a Jar Experiment
A variation of the cloud in a bottle experiment, this one requires a glass jar and some ice.
Before you begin, gather these supplies:
- Glass jar
- Jar lid or plate
- Warm water
With only a few steps, give your students an up-close look at a cloud.
- Pour the hot water into a jar, until it is about halfway filled. Make sure the water is not too hot or that you have warmed the jar ahead of time — pouring hot water into a cold jar could cause the glass to crack!
- Twist the lid back on the jar, or cover the opening with a plate. Place some ice on top of the lid or dish.
- Let the jar sit for a little while and see that the hot water is creating some steam.
- Light a match and allow it to burn for a few moments. Blow out the match, drop it into the jar and quickly cover the opening with the plate of ice.
- The “cloud” will be much more visible. Lift the lid and see the cloud fade into the room.
The same principles are at work in this experiment as in the cloud-in-a-bottle process. To form, a cloud needs water vapor, air debris and a change in temperature and pressure. In this experiment, instead of squeezing the bottle, the ice drops the air temperature and pressure inside of the jar and a cloud is born.
Awaken Your Child’s Curiosity
At Science Explorers, we are dedicated to making science fun and engaging for your children. We use interactive and hands-on techniques to foster a kid’s natural wonder and curiosity. Some of our favorite activities include dissection, rocket launches, rubber eggs and tornadoes-in-a-bottle, to just name a few.