Water in the Atmosphere

Water in the Atmosphere

Middle School

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Learning Objectives

• Describe the key processes of the water cycle, like evaporation and condensation.

• Explain how the sun's energy and gravity drive the movement of water.

• Model the different paths water takes through the atmosphere, land, and oceans.

• Define relative humidity and identify the common types of precipitation.

Key Vocabulary

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Water Cycle

The water cycle is the continuous movement of water on, above, and below the Earth's surface.

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Evaporation

Evaporation is when liquid water is heated by the sun and turns into invisible water vapor gas.

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Condensation

Condensation occurs when water vapor in the air cools down and changes back into liquid water droplets.

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Crystallization

Crystallization is the process where water vapor in the atmosphere turns directly into solid ice crystals.

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Transpiration

Transpiration is the process of plants releasing water vapor from their leaves into the air.

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Precipitation

Precipitation is any form of water, like rain or snow, that falls from clouds to Earth.

Key Vocabulary

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Gravity

Gravity is the force that pulls objects towards the center of the Earth, keeping us grounded.

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Relative Humidity

Relative humidity measures the percentage of water vapor present in the air versus its maximum holding capacity.

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Dew Point

The dew point is the temperature at which air becomes saturated and water vapor starts to condense.

The Cycle's Engines: Sun and Gravity

• The water cycle is powered by the sun’s energy and gravity.

• Solar energy causes water to evaporate and rise into the atmosphere.

• Gravity pulls water back down to Earth as precipitation.

Multiple Choice

What are the two main forces that power the water cycle?

• The sun's energy and gravity

• The wind and the clouds

• The oceans and the rivers

• The moon and the tides

Multiple Choice

What is the specific role of the sun's energy in the water cycle?

• It provides the energy to make water evaporate and rise.

• It pulls water vapor back down to the ground.

• It causes clouds to form from water vapor.

• It turns water vapor directly into ice.

Multiple Choice

If solar energy causes water to rise into the atmosphere, what would most likely happen if the force of gravity was removed?

• Water vapor would not be pulled back down to Earth as precipitation.

• The sun would no longer have enough energy to cause evaporation.

• Oceans would immediately freeze over.

• Water would evaporate much more slowly.

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The Water Cycle: Entering the Atmosphere

Evaporation

• Evaporation is the main way water enters the atmosphere from the Earth’s surface.

• The sun's energy heats up liquid water found in the planet's oceans and lakes.

• This process turns the liquid water into an invisible gas called water vapor.

Transpiration & Respiration

• Plants release water vapor from their leaves in a process called transpiration.

• Animals and people release water vapor into the atmosphere every time they breathe out.

• This release of water vapor when breathing out is a process called respiration.

Multiple Choice

What is the main process by which water from the Earth's oceans and lakes is turned into water vapor in the atmosphere?

• Evaporation

• Transpiration

• Respiration

• Condensation

Multiple Choice

What do the processes of evaporation, transpiration, and respiration have in common?

• They all require energy from the sun to occur.

• They all release water vapor into the atmosphere.

• They are processes that only happen in animals.

• They all turn water vapor back into liquid water.

Multiple Choice

If the amount of energy from the sun reaching Earth were to decrease significantly, what would be the most likely impact on how water enters the atmosphere?

• The rate of evaporation from the Earth's oceans and lakes would decrease.

• The rate of transpiration from plants would increase.

• Animals would stop releasing water vapor through respiration.

• The amount of water vapor released by plants and animals would be greater than the amount from evaporation.

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Condensation & Crystallization

Condensation

• Condensation is when water vapor gas cools down and changes into liquid water.

• Water vapor needs a surface to condense on, such as a tiny dust particle.

• The temperature at which this process begins is called the dew point.

Crystallization

• Crystallization is when water vapor cools below freezing and turns directly into ice.

• This important process is responsible for the formation of snow and frost.

• Clouds can form high in the atmosphere through this process as well.

Multiple Choice

What is condensation?

• The process of water vapor cooling and changing into liquid water.

• The process of liquid water heating and changing into a gas.

• The process of water vapor turning directly into ice.

• The process of liquid water turning into a solid below freezing.

Multiple Choice

How are condensation and crystallization different?

• Condensation forms liquid water when water vapor cools, while crystallization forms ice when it cools below freezing.

• Condensation only happens on surfaces like dust, while crystallization only happens on grass.

• Condensation is responsible for snow, while crystallization is responsible for clouds.

• Condensation begins at the freezing point, while crystallization begins at the dew point.

Multiple Choice

On a very cold winter day, you see delicate ice patterns, or frost, covering the outside of a window. Which statement best explains why this frost formed?

• Water vapor in the air cooled below freezing and turned directly into ice on the windows.

• Liquid water from the air froze onto the windows.

• Water vapor cooled to its dew point and formed a liquid on the windows.

• Snow from the atmosphere fell and stuck to the windows.

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Understanding Humidity

Humidity

• ​Humidity measures the total amount of water vapor that is currently present in the air.

• ​​The air's capacity to hold this water vapor is dependent on its current temperature.

• ​Warmer air has the ability to hold a greater amount of water vapor than cooler air.

Relative Humidity

• ​This is a percentage comparing current water vapor to the maximum possible at that temperature.

• ​​It provides a more useful measure of how "full" the air is with water.

• ​When relative humidity reaches 100%, the air is saturated and cannot hold any more water.

Multiple Choice

What does humidity measure?

• The total amount of water vapor present in the air.

• The temperature of the air compared to the ground.

• The percentage of clouds covering the sky.

• The speed at which the wind is currently blowing.

Multiple Choice

What is the relationship between air temperature and the air's capacity to hold water vapor?

• Warmer air can hold more water vapor, while cooler air can hold less.

• Cooler air can hold more water vapor, while warmer air can hold less.

• Air temperature has no effect on how much water vapor it can hold.

• Only air at very low temperatures can hold any water vapor.

Multiple Choice

If the relative humidity is 100%, what conclusion can be drawn about the state of the air?

• The air is saturated and cannot hold any more water vapor at its current temperature.

• The air has no water vapor in it at all.

• The air needs to become much warmer to feel humid.

• The temperature is about to drop significantly.

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Water Leaves the Atmosphere: Precipitation

• Precipitation is any form of water that falls from clouds to Earth’s surface.

• ​It happens when water droplets in clouds get heavy and gravity pulls them down.

• Rain is the most common form; smaller droplets are called drizzle or mist.

• Freezing precipitation includes snow, sleet, freezing rain, and hail.

Multiple Choice

What is precipitation?

• Any form of water that falls from clouds to Earth's surface.

• Water that is evaporating from the ground into the air.

• The process of clouds forming in the atmosphere.

• Water droplets that are too light to fall from the sky.

Multiple Choice

What causes water droplets or ice crystals in a cloud to fall to Earth?

• They become large and heavy enough for gravity to pull them down.

• They are pushed out of the cloud by strong winds.

• They turn into a gas and float down to the ground.

• They absorb sunlight and become warmer than the air.

Multiple Choice

If the air temperature is below freezing from the cloud all the way to the ground, which form of precipitation is most likely to fall?

• Rain

• Drizzle

• Snow

• Mist

Types of Freezing Precipitation

• Snow forms from ice crystals that clump together into snowflakes.

• Sleet is raindrops that freeze into ice before hitting the ground.

• Freezing rain is liquid rain that freezes on cold surfaces.

Multiple Choice

Which type of precipitation is formed when ice crystals clump together into flakes?

• Snow

• Sleet

• Freezing rain

• Hail

Multiple Choice

What is the main difference in how sleet and freezing rain are formed?

• Sleet freezes into ice before it hits the ground, while freezing rain freezes after hitting a cold surface.

• Sleet is made of large ice chunks, while freezing rain is made of small ice crystals.

• Sleet falls during the summer, while freezing rain falls during the winter.

• Sleet is a type of snow, while freezing rain is a type of melted hail.

Multiple Choice

During a winter storm, liquid rain falls and immediately forms a layer of ice on a car's cold windshield. What is the best explanation for this?

• Freezing rain, because it freezes on contact with cold surfaces.

• Sleet, because it is already frozen into ice pellets.

• Snow, because snowflakes are sticking to the car.

• Hail, because it is a storm of ice balls.

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Water's Pathways on Earth

• After precipitation, gravity pulls water downhill as surface runoff into streams and rivers.

• Water can be stored for long periods in lakes, glaciers, and aquifers.

• Plants take water from the ground and release it through a process called transpiration.

• Animals release water through respiration and decomposition when they die.

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Multiple Choice

What is the primary way that precipitation moves across Earth's surface to form rivers?

• Gravity pulls it downhill into streams and rivers.

• Plants release it through their leaves.

• It is stored for long periods in glaciers.

• Animals release it when they breathe.

Multiple Choice

What is a key similarity between how plants and animals affect water's pathways?

• They both store water underground in aquifers.

• They both release water back into the environment.

• They both get all their water from lakes.

• They both rely on gravity to move water.

Multiple Choice

If a forest is cleared and the land is paved over, what is the most likely effect on the water cycle in that area after a rainstorm?

• More water would be stored in underground aquifers.

• More water would be released through transpiration.

• Surface runoff into streams and rivers would increase.

• The amount of water stored in glaciers would decrease.

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Common Misconceptions

Misconception	Correction
Clouds are made of water vapor.	Clouds are tiny water droplets or ice crystals. Water vapor is invisible.
Air that feels dry has no water in it.	Even dry air has water vapor; it just has low relative humidity.
Gravity only pulls rain down.	Gravity also moves water in rivers and glaciers across the land.
Raindrops look like teardrops.	Small raindrops are spheres. Large ones flatten on the bottom while falling.

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Summary

• The sun's energy drives evaporation, and gravity causes precipitation.

• Water moves into the atmosphere as vapor through evaporation and transpiration.

• Water vapor cools and condenses to form clouds, leading to precipitation.

• The air temperature determines if precipitation is rain, snow, sleet, or hail.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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