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Screen capture from the MinuteEarth video “Why are there clouds?”

Screen capture from the MinuteEarth video “Why are there clouds?”

STEM in Context

How Do Clouds Form?

Let's Talk Science
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Summary

Learn how cumulus clouds form.
Why Are There Clouds? (2015) by MinuteEarth (3:14 min.).

When you think of clouds, what do you think of? Do you picture fluffy-looking masses that look like cotton? If so, you’re thinking of cumulus clouds! Today we’re going to take a look at how these clouds form.

How do clouds form?

Cumulus clouds start forming when solar energy causes liquid water on Earth to evaporate. Water, like all matter, is made up of molecules. Heat from the Sun breaks apart the bonds holding the liquid water molecules together. This forms water vapour. The warm air filled with water vapour starts to rise. Cooler air surrounds this pocket of warm, moist air, sinking below it and eventually pushing it upwards. The result is a warm, moist, invisible pocket shaped like a hot-air balloon. 

Invisible hot-air balloon pocket beginning to rise
Invisible hot-air balloon pocket beginning to rise (Source: MinuteEarth video Why are there clouds?)

 

You think with all that water vapour that the air would not be able to rise. Wrong! The more moisture the air has, the lighter it is. This has to do with the properties of water vapour, which is a type of gas.

Most of our atmosphere is made up of nitrogen and oxygen gas. Water molecules (H2O) are made up of two hydrogen atoms and one oxygen atom. These molecules are lighter than both nitrogen gas (N2) and oxygen gas (O2) molecules. Therefore, water vapour rises in the atmosphere. So warm, humid air (which contains many water molecules) is less dense than warm, dry air.

Air with more water molecules has less mass than air with more nitrogen gas or oxygen gas
Air with more water molecules has less mass than air with more nitrogen gas or oxygen gas (Source: MinuteEarth video Why are there clouds?).

 

As the invisible pocket of warm, moist air rises, the pressure around it drops. This allows the pocket of air to expand. As the pocket expands, the heat within it spreads out. This causes its overall internal temperature to drop. As the pocket continues to rise, the molecules of water vapour at the top of the pocket begin to condense again in the cool air of the atmosphere. This means that the molecules of water vapour begin to turn into tiny droplets of liquid water in the air. 

Misconception Alert

Clouds are not made of water vapour! They are made of liquid water.

As the water vapour condenses, the beginnings of a cloud can be seen. As the rest of the warm, moist air pocket rises, it will also cool and condense. This is what creates a cloud with a flat bottom that appears to grow tall and fluffy! 

As the droplets condense, the water molecules release the solar energy they gained when they evaporated. This energy heats the air surrounding the newly formed cloud, causing the cloud to rise, giving it lift. As the cloud continues to rise, more air is sucked up below it. This causes more and more air to rise, cool, and condense. As this happens, the cloud will grow larger and larger! 

As the cloud continues to rise, more air is sucked up below it
As the cloud continues to rise, more air is sucked up below it. This causes more and more air to rise, cool, and condense (Source: MinuteEarth video Why are there clouds?).

 

What happens next depends on the size of the cloud, and how much energy it releases. If the supply of water vapour molecules is very large and a lot of energy is released, then very tall cumulonimbus clouds can form. These are the storm clouds responsible for thunderstormstornadoes, and even hurricanes.

Did you know? 

The amount of energy released from a small cumulus cloud is equivalent to about 270 tonnes of dynamite!

So remember: there is a lot of physics and chemistry going on behind the scenes of those fluffy-looking shapes in the sky!

 

Starting Points

Connecting and Relating
  • When you see clouds, how do they make you feel? Explain.
  • Have you ever wondered why there are different types of clouds?
  • Have you ever flown in a plane above the clouds? If so, how did the clouds look from above?
Connecting and Relating
  • When you see clouds, how do they make you feel? Explain.
  • Have you ever wondered why there are different types of clouds?
  • Have you ever flown in a plane above the clouds? If so, how did the clouds look from above?
Relating Science and Technology to Society and the Environment
  • When we describe the weather as bad weather, it often means there are clouds in the sky. Identify specific ways in which cloud formation, and the energy associated with it, can cause significant damage.
  • Many people hope for clear blue skies on a daily basis. But would constant clear blue skies be a good thing for society? For the environment? Identify and discuss some reasons why it might not be. 
Relating Science and Technology to Society and the Environment
  • When we describe the weather as bad weather, it often means there are clouds in the sky. Identify specific ways in which cloud formation, and the energy associated with it, can cause significant damage.
  • Many people hope for clear blue skies on a daily basis. But would constant clear blue skies be a good thing for society? For the environment? Identify and discuss some reasons why it might not be. 
Exploring Concepts
  • What role does the hydrological cycle (water cycle) play in cloud formation? Identify the processes involved.
  • How is solar energy transferred during the cloud formation process?
  • Why does water vapour rise into the atmosphere?
  • Why don’t all clouds become cumulus clouds? (This will require additional research)
Exploring Concepts
  • What role does the hydrological cycle (water cycle) play in cloud formation? Identify the processes involved.
  • How is solar energy transferred during the cloud formation process?
  • Why does water vapour rise into the atmosphere?
  • Why don’t all clouds become cumulus clouds? (This will require additional research)
Nature of Science/Nature of Technology
  • How do you think our understanding of cloud formation helps with the forecasting of weather? Explain.
Nature of Science/Nature of Technology
  • How do you think our understanding of cloud formation helps with the forecasting of weather? Explain.
Media Literacy
  • Clouds are an everyday experience in our lives. In fact, we often celebrate them in song and video. Why do you think this is? Explain.
Media Literacy
  • Clouds are an everyday experience in our lives. In fact, we often celebrate them in song and video. Why do you think this is? Explain.
Teaching Suggestions
  • This video and article can be used to support teaching and learning of earth science and weather related to clouds. Concepts introduced include solar energy, evaporation, water vapour, condensation, pressure, and lift.
  • After viewing the video and reading the article, teachers could have students consolidate learning by looking critically at the video and completing a Video Review learning strategy. Download ready-to-use Video Review reproducibles using the for this video in [Google doc] and [PDF] formats. 
  • To consolidate understanding of the concept of cloud formation, teachers could have students use a Concept Definition Web learning strategy. Download ready-to-use Concept Definition Web BLMs for this video in [Google doc] and [PDF] formats.
Teaching Suggestions
  • This video and article can be used to support teaching and learning of earth science and weather related to clouds. Concepts introduced include solar energy, evaporation, water vapour, condensation, pressure, and lift.
  • After viewing the video and reading the article, teachers could have students consolidate learning by looking critically at the video and completing a Video Review learning strategy. Download ready-to-use Video Review reproducibles using the for this video in [Google doc] and [PDF] formats. 
  • To consolidate understanding of the concept of cloud formation, teachers could have students use a Concept Definition Web learning strategy. Download ready-to-use Concept Definition Web BLMs for this video in [Google doc] and [PDF] formats.

Learn more

The 10 Basic Types of Clouds (2019)

Article by Tiffany Means for ThoughtCo describing the ten most common forms of clouds, how to recognize them, and some tips on when you’re most likely to see them. 

Forming Cumulonimbus (Timelapse) (2013)

Timelapse video (1:43 min.) by Kjoenbongarit showing the formation of cumulus clouds and their further development into cumulonimbus clouds.

References

Lumen Physical Geography. (n.d.). Atmospheric gasses.

Met Office. (n.d.). Cumulus cloud.

UCAR Center for Science Education. (2019). Clouds and how they form.

Web Weather for Kids Cloud Science. (n.d.). Cumulus clouds. University Corporation for Atmospheric Research.