Water Cycle

Water Cycle

Middle School

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Learning Objectives

• Describe the main stages of the water cycle and its continuous movement.

• Explain the role of the Sun's energy and gravity in driving the water cycle.

• Identify how water changes states between solid, liquid, and gas.

• Connect the water cycle to weather and its importance for all living things.

Key Vocabulary

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Evaporation

The process where liquid water heats up, turns into a gas, and rises into the air.

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Condensation

The process where water vapor cools and changes back into tiny liquid water droplets, forming clouds.

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Precipitation

Water that falls from the clouds to the Earth as rain, snow, sleet, or hail.

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Transpiration

The evaporation of liquid water from plants and trees into the Earth's atmosphere through their leaves.

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Infiltration

The process by which water on the ground surface soaks into the soil and underlying rock.

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Runoff

Precipitation that does not soak into the ground but instead flows over the surface of the land.

What is the Water Cycle?

• Water continuously moves between Earth's surface and the atmosphere.

• This natural recycling process is called the water cycle.

• The cycle is powered by the sun's energy and the force of gravity.

Multiple Choice

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

• The Sun's energy and gravity

• Earth's rotation and magnetism

• Wind and ocean currents

• Moon's gravity and geothermal heat

The Three States of Water

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Solid (Ice)

• Molecules are packed tightly together in a fixed structure.

• They are held close together and have very little movement.

• Glaciers and ice caps are examples of water in solid form.

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Liquid (Water)

• In liquid water, molecules are close but can move around.

• The molecules can easily slide and flow past one another.

• Oceans, rivers, and lakes are all examples of liquid water.

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Gas (Water Vapor)

• In its gas form, molecules are spread very far apart.

• They move around freely and quickly in all different directions.

• Water vapor is usually invisible, but steam is a visible example.

Multiple Choice

Which state of water is described as having molecules that are spread far apart and move freely?

• Liquid

• Gas (water vapor)

• Plasma

• Solid (ice)

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Where Earth's Water is Stored

• Water is stored in various places called reservoirs as it moves.

• The vast majority of Earth's water is stored in the oceans.

• Other reservoirs are the atmosphere, ice, snow, and groundwater.

• Lakes, streams, and all living things (the biosphere) also hold water.

Multiple Choice

According to the content, where is most of Earth's water stored?

• In glaciers and ice caps

• In the atmosphere

• In the oceans

• In groundwater

Processes: From Water to Vapor

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Evaporation

• Liquid water is heated by the sun and becomes water vapor.

• This gas then rises high up into the air.

• Most evaporation happens from oceans, leaving the salt behind.

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Transpiration

• Transpiration is the evaporation of water from plant leaves.

• Plants absorb water from the soil through their roots.

• This water then moves to the leaves and evaporates.

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Sublimation

• Sublimation is a process where a solid turns into a gas.

• This happens when snow and ice turn directly into vapor.

• This process completely skips the liquid water melting phase.

Multiple Choice

What is the key difference between evaporation and transpiration?

• Transpiration creates liquid water, while evaporation creates water vapor.

• Transpiration is evaporation from plants, while evaporation is from bodies of water.

• Evaporation happens on land, while transpiration happens over oceans.

• Evaporation involves heat, while transpiration does not.

Processes: Forming Clouds

• Condensation is when water vapor cools and becomes liquid water droplets.

• These droplets gather on dust particles in the air to form clouds.

• Crystallization is when water vapor turns directly into solid ice crystals.

Multiple Choice

How are clouds formed in the atmosphere?

• Ice crystals melt and form large water droplets.

• Water vapor sublimates directly into clouds.

• Liquid water is heated by the sun until it floats.

• Water vapor cools and condenses on dust particles.

How Water Returns and Moves on Earth

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Precipitation

• ​Precipitation is any water that falls from the clouds to Earth.

• ​​This includes different forms like rain, snow, sleet, and hail.

• ​It happens when water in clouds gets too heavy to float.

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Runoff

• ​Runoff is water from rain that flows over the land’s surface.

• ​​This happens when the ground cannot absorb any more water quickly.

• ​This extra water will then flow into rivers, lakes, or oceans.

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Infiltration

• ​Infiltration is the process of water soaking into the soil.

• ​​Some of this water is used by plants as soil moisture.

• ​Water can also go deeper to become part of the groundwater.

Multiple Choice

What is the difference between runoff and infiltration?

• Runoff flows over the land, while infiltration soaks into the ground.

• Infiltration is rain, while runoff is snow.

• Infiltration flows over the land, while runoff soaks into the ground.

• Runoff is rain, while infiltration is snow.

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Common Misconceptions About the Water Cycle

Misconception	Correction
Clouds are made of water vapor.	Clouds are made of tiny water droplets or ice crystals.
Water disappears when it evaporates.	Water changes into an invisible gas called water vapor.
The water cycle has a starting and ending point.	The water cycle is a continuous process with no beginning or end.
Ocean water that evaporates is salty.	When ocean water evaporates, the salt is left behind.

Multiple Choice

What is the primary role of the Sun's energy in the water cycle?

• It helps water soak into the ground.

• It causes precipitation to fall from the clouds.

• It pushes water downhill as runoff.

• It provides the energy for evaporation and transpiration.

Multiple Choice

Which of these describes the process of transpiration correctly?

• Water flowing over the land after it rains.

• Water vapor turning into liquid water.

• Plants releasing water vapor from their leaves.

• Water turning into ice crystals in clouds.

Multiple Choice

A town replaces a large forest with roads and parking lots. How will this change most likely affect the local water cycle?

• It will increase runoff and decrease infiltration.

• It will decrease the amount of precipitation.

• It will increase the rate of transpiration.

• It will decrease runoff and increase infiltration.

Multiple Choice

Analyze the journey of a water molecule that starts in the ocean, becomes part of a cloud, and then falls on land. Which sequence of processes does it follow?

• Sublimation, Precipitation, Infiltration

• Evaporation, Infiltration, Transpiration

• Evaporation, Condensation, Precipitation

• Transpiration, Condensation, Runoff

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Summary

• The water cycle is the continuous movement of water, driven by the sun.

• Water moves through evaporation, condensation, transpiration, and precipitation.

• Water is stored in reservoirs and exists as a solid, liquid, or gas.

• Human activities can impact the rates of evaporation and precipitation.

Poll

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

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