# How Does the Water Cycle Work? | DFRobot Science Lab Season 2 EP07

### Standards

NGSS

5-PS1-1 Develop a model to describe that substance is composed of small and invisible particles

5-PS2-1 Demonstrate that the gravity effect of the earth on objects is downward

5-ESS2-1 Develop a model to describe how the lithosphere, biosphere, hydrosphere, and atmosphere interact with each other.

MS-ESS2-4 Develop a model to describe the circulation of water in the earth system driven by solar and gravitational potential energy.

### Overview

This lesson will lead students to think about the question "where does the rainwater come from and where does it go?", observe the movement of water droplets on the glass of ice water. By using soil, water and plastic box to build a simple water cycle model, they will explore the formation process of the water cycle, learn the three forms of water and the distribution of water on the earth, and understand the dynamic process of the water cycle and what role water cycle plays in the lithosphere, biosphere, hydrosphere and atmosphere.

### Materials

Play and Learn with Boson Science Design Kit: https://www.dfrobot.com/product-2176.html

Engage

When it rains, we can see the rainwater dropping like beads. Have you ever wondered where does the rain come from? When the rain fell on the ground, the ground became wet; after the rain stopped, the ground slowly dried out. Where did the rain go?

In nature, there are many kinds of water, such as rainwater, seawater, etc. So, will the rain become less and less? Will the sea water amount increase continuously? Have your guess!

Explore

This experiment will be divided into two parts. In the first part, we are going to add some ice cubes into a glass of water, and observe the movement of water on the outer cup wall. In the second part, we are going to build a simple water cycle model, using soil and water to create land and ocean in the experiment box, and then explore the process of water cycle between land and sea.

Part 1 Observation: Is the Water Moving?

Add the ice cubes into the water, observe the changes on the outer cup wall, and record it in the table below.

### Activity Conclusion

The referable results are as follows:

We see that the outer wall of the cup has become wet, and a lot of small droplets have gathered. Think about it, where does the droplets come from?

First of all, the small droplets must not flow out of the cup, or the cup is leaking. Considering that the outer cup wall is only in contact with the air, we speculate that there may be water in the air! It’s just that the water in the air is so small that we can’t see it. When it comes to a cold cup, the water in the air gathers together and becomes small drops on the outer cup wall!

In the same way, it can be speculated that the rain on the ground will dry out, perhaps it is because that the water on the ground returns to the air. The water in the air can gather on the cup wall, and the water on the ground can also return to the air. This indicates that the water is moving!

### Conjecture

In nature, will water in rivers, lakes and seas move into the air? How did the water in the air turn into rain and return to the ground? How does the natural water cycle change? Let's continue to explore through experiments.

Part 2 Experimental Exploration: How Is Water Cycle Formed？

We are going to make a land-water model to explore the water cycle in nature.

In a plastic box, half of the space is the land created by soil and half is the ocean created by water. Seal the plastic box with plastic wrap to prevent water in the outside air from interfering with the experiment. Observe the formation process of the water cycle, and use BOSON soil moisture sensor to detect changes in soil moisture in the model.

### Materials

Prepare the following BOSON modules and other materials.

### Step

1. First, build an experimental circuit to detect the soil moisture value.

2. After completing the circuit connection, let’s build the water cycle model together.

Soil Moisture Value Table:

### Activity Conclusion

Soil Moisture referable data:

Through the experimental data, we can know that although the moisture of the soil does not change much, the value is still generally getting higher.

In the water cycle model we created, we can clearly see that under the heating of the sun, the plastic box is full of water vapor. This is because the water in the "lake" evaporates into the air. When the water in the air increases, encountering the cold ice cubes on the plastic wrap, it will condense together and turn into small droplets, and then drop into the soil. Is this similar to the process of rain?

By the same token, in nature, the heat of the sun will cause the water on the sea surface to evaporate into the air, and it will condense in the sky and form clouds. With more and more small droplets in the clouds, rain will form and fall on the ground, flow into the river, and eventually part of the water return to the ocean. This is the water cycle!

Science Background

Through experiments, we have a general understanding of the water cycle among the ocean, air and land. Let’s get to learn the water cycle between water and nature together!

### Three Forms of Water

We all know that when water freezes, it turns into ice, and boiling water will evaporate into water vapor. In physics, ice is called solid water, water vapor is called gaseous water, and normal water is called liquid water. The three forms of water are composed of individual water molecules with different distances between the molecules.

The distance between the water molecules of ice is large, and the water molecules combine with each other and hardly move, so the shape of ice is fixed. The distance between the water molecules of liquid water is small, and the water molecules can move freely, so the liquid water can become various shapes. Water vapor has the largest distance between water molecules, the water molecules move so fast that the human eye can’t see the water vapor.

We can see the white steam on the boiling kettle mouth, because the water vapor is cooled by the surrounding air and turned into small droplets.

### Water Cycle in Nature

Due to the three types of changes of water form, the water in nature can circulate continuously.

The heat of solar radiation evaporates a large amount of water from the sea, lakes, rivers and land, turning into water vapor and moving into the air. When the water vapor in the air encounters cold temperature, it will turn into a cloud, and more and more water droplets in the cloud will fall to the ground as rain or snow. The rainwater that falls on the ground may evaporate again, or it may be transformed into groundwater, soil water and surface runoff, and eventually part of the water returns to the ocean, thus a natural cycle is formed.

### The Water Cycle and Other Cycles

The water cycle drives the interaction among the lithosphere, biosphere, hydrosphere, and atmosphere on the earth, and is the "tie" that connects the earth’s circles and various water forms.

The water cycle is a "regulator", it regulates the energy among the various layers of the earth, and plays an important role in the change of cold and warm climate. The water cycle is the "sculptor", which shapes the colorful surface forms through erosion, transportation and accumulation. The water cycle is the "conveyor belt", it is the powerful driving force and main carrier of the surface material migration. More importantly, through the water cycle, the ocean continuously delivers fresh water to the land, supplementing and renewing fresh water resources on the land, thus making water a renewable resource.

Conclusion

In this project, we started from "where does the rain come from, and where does it go?", through a cup of ice water, observed the phenomenon of water movement. Then built a simple water cycle model, explored the formation process of the water cycle, and learned the knowledge of water and water cycle.

The project is going to an end, please remove cables, and put all the BOSON modules back into the kit according to the corresponding position.

Extend

1. Water will become larger when it freezes into ice. Why is this? Try to explain from the perspective of water molecules.

2. In autumn and winter mornings, heavy fog often affects our sight. Do you know how the fog is formed?

3. Why do we feel the air more humid in places with many trees?