The Water Cycle
With the help of Luke Warm, a weatherman on the water channel, two young baseball players come to understand why the big game might be rained out as they are introduced to the key elements that make up and affect the water cycle. They discover the amazing process by which the Earth's water supply has been recycled over millions of years, centering on three stages: evaporation, condensation and precipitation. They follow the trail water takes after it falls from the sky and passes through each of these three stages.
Follow the trail water takes through its three stages: evaporation, condensation, and precipitation.
- Students will realize that water is everywhere. It is always moving from the earth's surface into the air and back to the surface again. This constant movement and changing of water is called the water cycle.
- Students will know that about seventy percent of the earth is covered with water. Almost all of that water is salty water found in the oceans. Most of the remaining water (fresh water) is frozen in glaciers or polluted, leaving only a small amount of fresh water that is usable to living things.
- Students will understand that water is made up of tiny particles called molecules. The position and interaction of these molecules determine the form of the water. When water is a solid (ice), the molecules are not free to move around very much. When water is liquid, the molecules are able to slide freely around one another. When water is a gas, the molecules are very far apart, and they fly around one another.
- Students will know that water changes states because it absorbs and releases heat energy from the sun.
- Students will understand how evaporation is involved in the water cycle. When liquid water is heated, the water molecules start to move very quickly. They will fly off into the air, or evaporate, into an invisible gas (water vapor). How quickly water evaporates depends on how much heat is added. The sun heats and evaporates hundreds of thousands of gallons of water on the earth's surface every day. Most of this evaporated water comes from the oceans.
- Students will understand how condensation is involved in the water cycle. If you take heat away, or cool, a gas, the molecules will slow down. They actually move closer together and condense into a liquid. Water vapor condenses to form tiny droplets of water so small they can float in air. This is what makes up clouds and fog. If it is cold enough, the droplets will freeze into ice crystals.
- Students will know the types of precipitation and how they form.
- When water droplets in clouds get too heavy, gravity pulls them to the earth. This is rain. Sometimes raindrops might start out as a solid, but the warm air near the earth melts the ice as it falls through the air.
- Snowflakes are made up of small crystals of frozen water. The crystals gather together as they fall and form snowflakes.
- Hail is made up of pieces of ice that fall a little ways and then are blown back up into the air by wind. Each time a piece of hail goes up and down through the air, it collects more water and gets bigger. Finally, it gets big enough that the wind cannot blow it up again, and the hailstone falls to the ground.
- Sleet is made up of raindrops that freeze as they fall to the earth. Sleet is smaller than hail.
- Students will understand what happens to water after it falls to the earth.
- Most precipitation falls onto the oceans, but some falls on land. Precipitation that falls over land may fall directly into rivers and lakes.
- Some of the precipitation that falls on the land runs across the ground and drains into streams and rivers. This is called runoff. The rivers and streams will eventually take the water to the oceans.
- Other precipitation that falls over the land soaks into the ground and becomes groundwater. Groundwater is water that moves under the earth's surface through small spaces in rocks and soil. Some groundwater eventually seeps into streams and rivers.
- Other groundwater is absorbed by plant roots. The water is used by the plant and then released back into the air. This is called transpiration.
- The rest of the precipitation that falls onto the land evaporates back into the air.
- Students will realize that the amount of time it takes for water to go through the cycle can be very short or very long, depending on where the water goes and what happens to it.
- Before viewing the video
- Lead a brief discussion by asking a few questions. Where does the water that makes up raindrops come from? How does the water get into the air? Has the water in the oceans always been there? See what ideas your students have.
- After viewing the video
- Do a visual representation of what the earth's water is like (approximately 97% is saltwater, 2% found in glaciers and ice, and 1% is usable freshwater). You can use 100 blocks or marbles and separate them into three appropriately sized groups, or you could show the students how to draw a pie chart representing the earth's water.
- Demonstrate condensation. If it is humid enough, set a glass of ice water in the room. Within a few minutes, water droplets will be seen on the outside of the glass. Ask the students where the water came from. Explain that the water did not come from inside the glass but that the air in the room has water vapor in it. The cold temperature of the glass caused some of the water vapor in the air to condense onto the glass. NOTE: Some dry climates night not be suitable for this demonstration. If that is the case, you could still lead a discussion on the subject. Most students will remember seeing condensation on the outside of a glass at some time or another.
- The Water Molecule
- The Sun
- Where Does Water Go?