Water Flow

In this unit, students explore the phenomena of Earth landforms and the water cycle. Once students have modeled landforms and created maps showing the shapes and kinds of land and bodies of water, students analyze how water moves over the land as it flows downhill because of gravity and cycles between solid and liquid depending on the amount of heat present. This page showcases excerpts from the second lesson in this unit.

Science Background for Teachers:

The background information provides teachers with more in-depth explanations of the science phenomena being studied in this unit. In this case, students explore the topic of how water flows on Earth.

Water on Earth does not stay in one place. Instead, it is constantly on the move, fueled by heat from the sun and carried through the atmosphere. As it moves, it changes from solid to liquid and gas and back to solid depending on the amount of heat present. The circulation of water through the hydrosphere from water that has collected on Earth’s surface to the atmosphere and back is called the water cycle.

With enough energy from the sun, liquid water on Earth’s surface evaporates into the atmosphere. Evaporation is the process of liquid water changing into water vapor, its gas state. It is caused by the addition of heat, which causes water molecules to gain energy and speed up until they spread out completely, turning into a gas. As water vapor moves higher in the atmosphere, it transfers some of its heat back to the atmosphere. Eventually the water vapor will condense, changing from a gas back into liquid water. When this happens, the water droplets join with tiny pieces of dust, pollution, or other invisible particles that are floating in the air and form a tiny droplet around each particle. When billions of these droplets join, they form a cloud.

When the cloud cannot hold any more water, it falls to the ground as rain, sleet, hail, and/or snow. This is called precipitation. Gravity pulls the water droplets toward the ground because gravity is a force that pulls things toward each other. In other words, it is an attractive force between all matter. Earth’s gravity pulls everything on or near the surface down toward Earth’s center, which is why anything thrown up in the air falls back to the ground.

Supports Grade 2

Science Lesson: Exploring Water Flow

In this lesson, students first use paper “land” models to investigate where water goes when it rains on land and then plastic “mountain” models to investigate the cycling of water as heat causes mountain ice to change into liquid water and flow downhill. 

Science Big Ideas

  • Maps show us that water is found in different parts of Earth as a solid or a liquid.  
  • Liquid water on Earth’s surface flows downhill, pulled by Earth’s gravity.
  • Water on Earth doesn’t always stay in the same form. Like all matter, water can change from a solid to a liquid or from a liquid to a gas. It depends on the amount of heat present.

Sample Unit CTA-2
Discover Complete Hands-on Screens-off Core Science Curriculum for K-8 Classrooms

Prepared hands-on materials, full year grade-specific curriculum, and personalized live professional development designed to support mastery of current state science standards.

Science Essential Questions

  • How do we know where the ocean is on a map? How do we know where the land is on a map?
  • How are solids different from liquids?
  • Why does rain fall to the ground from the sky?
  • How else can we see the effect of Earth’s gravity pulling all things down to the surface?
  • What happens to rain once it falls to the surface?
  • Why does water flow downhill on both mountains and hills?  
  • How does adding heat change liquid water?
  • How is evaporation connected to clouds?  
  • What causes water to become a solid (ice or snow)? 

Common Science Misconceptions

Misconception: Water is found only in bodies of water.
Fact: Water is found in multiple places in addition to bodies of water. Its gas form, water vapor, is found in the atmosphere. Liquid water is also found underground. Finally, water is also found as solid ice or snow.
Misconception: Water isn’t recycled. When it rains, the rain drops are “new” water.
Fact: Water isn’t ever created or destroyed. Instead, it is always being recycled. It moves around the planet as it cycles between a solid, a liquid, and a gas depending on the amount of heat present.

Science Vocabulary

Body of water: a part of Earth’s surface that is filled with water

Gravity:  a force that pulls things toward each other

Landform: a natural feature on Earth’s surface

Map: a drawing or other model of an area of Earth’s surface

Water cycle:  the circulation of water from a collection to the atmosphere and back to Earth; includes evaporation, condensation, precipitation, and collection

Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

Solid Water

Ice and snow are both made of water. They are solid forms. Remember that one property of matter is whether it is a solid, a liquid, or a gas. Solids have their own shape. They keep this shape until something changes them by force.

Liquid Water

Oceans, rivers, and lakes are liquid water. Rain is also liquid water. Liquids have no shape of their own. They take the shape of their container. They also flow.

When it rains, liquid water falls from the sky to the ground. It is pulled down by gravity. Gravity is a force that pulls things toward each other. Earth’s gravity pulls all things down toward Earth’s center. Think about throwing a ball in the air. It always falls back to the ground because of gravity.

When rain falls to the ground, some of the water soaks into the ground. The rest of it begins to flow downhill over the land. This means it moves from high places to low places. Gravity pulls liquid water downhill. This is how rivers and streams form.


Hands-on Science Activity

In this lesson, students use models in two different investigations. In the first investigation, students investigate the question: “Where does water go when it rains on land?” In the second investigation, students investigate the question: “How does heat change mountain ice?” Students collaboratively carry out the two investigations to explore where water is found on Earth, the forms that it is found in (solid and liquid in this investigation), and how it changes form and moves over the land when heat is added. In both investigations, students use their models to analyze patterns in where water is found as a solid on Earth and where it is found as a liquid.

Science Assessments

KnowAtom incorporates formative and summative assessments designed to make students thinking visible for deeper student-centered learning.

  • Vocabulary Check
  • Lab Checkpoints
  • Concept Check Assessment 
  • Concept Map Assessment 
  • And More...


Science Standards

See How KnowAtom Aligns to NGSS Science Standards

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Download the Alignment to NGSS

Standards citation: NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.