You Will Discover
· How ocean water and fresh water are different
· How the water cycle gives us fresh water.
· What causes weather.
· How we predict weather.
Chapter 6
Water Cycle and Weather
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Build Background
How does Earth’s water affect weather?
Evaporation
Condensation
Precipitation
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Chapter 6
Vocabulary
Evaporation page 186
Condensation page 187
Precipitation page 187
humidity page 190
front page 191
meteorologist page 194
barometer page 194
anemometer page 195
wind vane page 195
Meteorologist Scientists called meteorologists study weather conditions.
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Lab Zone
Directed Inquiry
Explore How can you make fresh water from salt water?
Some countries without enough fresh water make fresh water from salt water.
Materials
salt water and spoon
small cup and bowl
plastic wrap and tape
marble
Process Skills
You can write, speak, or draw pictures to communicate information.
What to Do
1. Pour 5 spoonfuls of salt water into a bowl. Set a small cup in the middle of the bowl. Cover the bowl with plastic wrap.”
Tape the plastic wrap to the bowl The plastic wrap should not touch the small cup.
Place a marble above the small cup.
2. Place in sunlight for several hours.
3. Remove the marble, plastic wrap, and cup. Put the bowl and cup in a warm place. Let the water evaporate for about 3 days.
4. Observe the bottom of each container.
Explain Your Results
1. Communicate What did you find in the bottom of each container? Explain.
2. Predict Think about the variables that affect evaporation. How could you speed up evaporation? Describe how you could test your prediction.
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How to Read Science
Reading Skills
Cause and Effect
Linking causes and effects can help you better understand what you read. Writers sometimes communicate cause and effect with words such as because, since, so, and as a result.
• A cause may have more than one effect. An effect may have more than one cause. Sometimes an effect leads to another event, which creates a chain of causes and effects. Some of the causes and effects in the article are marked.
• You can use a graphic organizer to show cause and effect.
Newspaper Article
Skating on Thin Ice
A skater was rescued from icy waters in Lily Pond today. Last night temperatures dropped, causing the ice on the pond to thicken. In the chilly dawn, the skater glided over the ice. But the temperature rose, so the ice began to melt. As a result, the ice was much thinner at noon when the skater returned. Since the thin ice could not support his weight, the skater fell through the ice and into the water near the edge of the pond. He recovered quickly, because he was rescued right away.
Apply It!
Make a graphic organizer like the one shown to communicate the causes and effects in the newspaper article. If an event is BOTH a cause and an effect, you should write it in each box.
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You Are There!
You are gazing at Earth from space. The giant blue ball turns slowly. Huge chunks of brown and green with splashes of white creep into view, cross the blue ball, and disappear behind it. The chunks are Earth's continents and islands. The vast expanse of blue is the world's great ocean. Masses of white clouds drift across the lands and ocean. How does Earth's water affect why clouds form and how they move?
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Lesson 1
Where is Earth's water?
Any ocean that you might step into is linked to all the oceans in the world. The world's oceans connect to form one huge mass of salty water, with large and small areas of land.
Earth—The Water Planet
Throughout history, people have used bodies of water to travel from place to place. Because almost 4 of Earth's surface is covered with water, they had very little choice. Water provides a home and food for millions of Earth's organisms. In turn, these organisms are food for people.
Earth's water is always in one of three states. At a temperature of 0°C, water freezes into a solid called ice, and ice melts into water. At a temperature of 100°C, water becomes an invisible gas called water vapor.
Some of the water near Earth's surface is water vapor in the atmosphere. But more than 97/100 of Earth's water is in the oceans and the seas. The seas are smaller areas of the ocean. Most of the rest of Earth's water is frozen in glaciers and polar ice caps. Less than 1/100 is in rivers and lakes.
People have named sections of Earth's great ocean. The table shows the names and areas of some of the sections.
1. Checkpoint About how much of Earth's water is frozen in glaciers and ice caps?
2. Math in Science Look at the table above. About how much greater is the area of the Pacific Ocean than the area of the Atlantic Ocean?
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Salty Water
"Water, water, everywhere, Nor any drop to drink." These lines in a famous poem describe a crew on an ocean ship that has run out of drinking water. Water is all around them. How could they run out of drinking water?
If you have ever tasted ocean water, you know the answer. It tastes very salty. But taste is not the main problem. Ocean water is not healthy for drinking. Your body cannot use water that is as salty as ocean water.
But why is the ocean salty? Water is a liquid made up of hydrogen and oxygen. Ocean water is a mixture of water and many dissolved solids. Most of the salt in ocean water comes from rocks and soils on the land. Rivers carry dissolved salts and minerals to the ocean. The most common salt in the ocean is sodium chloride, the same salt that's in your saltshaker. The ocean supplies much of our table salt and some of our minerals.
Lakes and rivers make up a part of Earth’s fresh water.
Most of Earth’s fresh water is frozen in polar ice caps and glaciers.
Oceans and seas are filled with salty water. They cover most of Earth.
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Differences in Saltiness
Saltiness of the water near the ocean's surface varies from place to place. In warm, dry places, ocean water turns rapidly into water vapor in the air. The salt that's left behind makes the water even saltier. Some of the saltiest water on Earth is located in the Red Sea, which has deserts on three sides.
Ocean water is less salty near the North and iouth Poles. Less salt can dissolve in the cold water :here. And water turns to vapor more slowly in lower temperatures. The ocean is also less salty in areas where rivers, melting ice, or heavy rains add plenty Af fresh water. For example, many rivers flow into the 3altic Sea. Its water is less salty than most ocean water.
Most of Earth's water is salty ocean water. Most of Earth's fresh water is frozen in glaciers and ice caps. People cannot use it for drinking. They cannot use it to keep land plants and animals alive. Earth's liquid Fresh water is underground or in lakes, rivers, and streams. The water vapor in the air and the liquid and Frozen water that fall through the atmosphere are all Fresh water.
Lesson Checkpoint:
1. Why is the water in the Baltic Sea less salty than most ocean water?
2. Is the water in the Red Sea more or less salty than average? Explain your answer.
3. Cause and Effect Why is ocean water more salty than average in warm and dry places?
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Lesson 2
How do water and air affect weather?
Why do some places get lots of rain while other areas get very little? The way water moves in and out of the atmosphere affects our lives.
How Water Is Recycled
Earth's water is always being recycled. The never-ending movement of water from Earth's surface to its atmosphere and back again is called the water cycle. You can see an example of the water cycle as puddles disappear after a rain. Some water runs into drains that flow into lakes, rivers, or the ocean. The rest is in the air. Water is made of small particles that are constantly moving. As the Sun's energy warms the water, the particles move faster. They fly away from the liquid water and change into a gas called water vapor.
The process of changing liquid water to water vapor is called evaporation. The higher the temperature, the faster water changes from liquid to gas.
Evaporation
Water is stored in lakes, oceans, glaciers, marshes, soil, and spaces in rock. It evaporates in the Sun's warmth. Some water vapor also comes from the leaves of plants.
Condensation
When moist air rises, it cools. The water vapor in it condenses in the atmosphere. These tiny droplets of liquid water form clouds and fog.
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To understand the next step in the water cycle, think of what happens when you breathe on a cold window. The cold glass cools the water vapor in your warm breath. The water vapor turns into a liquid that fogs up the window. The process of water vapor becoming liquid water when it cools is called condensation.
Like the fog from your breath, a cloud is made of tiny drops of water or ice crystals. The drops and crystals combine with others until they become so large and heavy that gravity pulls them downward. Then they fall as precipitation, which is any form of water that falls to Earth. The cycle begins again.
The Sun's energy powers the water cycle that provides fresh water from the ocean. Temperature, air movement, and how much water vapor is in the air affect how quickly water evaporates and condenses. Because land features affect temperature, they affect the water cycle too. When wind blows moist air up one side of a mountain, clouds form there. More precipitation falls than on the other side of the mountain.
1 .Checkpoint What is the water cycle?
2. Technology in Science Old desalinators used evaporation and condensation to remove salt from ocean water. Use the Internet to find out how modern desalinators work.
Precipitation
Depending on air temperatures and wind conditions, the water may fall as rain, snow, or hail. If the air temperature in or below the cloud is above freezing, th water vapor will condense and fall as rain. If the air temperature is below fr~ezing, water falls as snow, sleet, or hail. Most precipitation falls on oceans.
Storage
The water from precipitation over land sinks into soil and underground pores in rock. Some water runs off the land or seeps from the ground into streams, rivers, and lakes. Most of it falls, flows, or seeps into the ocean.
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Earth's Atmosphere
When you look up on a clear day, you seem to see a high, blue ceiling. You are really looking through 9,600 km (about 6,000 mi) of air. The blanket of air that surrounds Earth is its atmosphere. Like other matter, air has mass and takes up space.
Air is made up of a mixture of invisible gases. Almost 4/5 of Earth's atmosphere is nitrogen. Most of the rest is oxygen, but small amounts of carbon dioxide gas are also present. The part of the atmosphere closest to Earth's surface contains water vapor. The amount of water vapor depends on time and place. For example, air over an ocean or a forest has more water vapor than air over a desert.
Gravity pulls the mass of air toward Earth's surface. The pushing force of air is called air pressure. Air pushes with equal force in all directions. At any moment, many kilograms of gas press down on your school building. They do not crush it because the air inside the building exerts pressure too. Air pushing down is balanced by air pushing up and sideways. Air pressure decreases as you go higher in the atmosphere.
Air Pressure
Air pressure also changes with temperature. As the air near Earth's surface warms, its particles move farther apart. The air pushes down with less pressure, and then it rises. An area of low pressure forms. If the air near Earth's surface cools, the particles in the air become more closely packed. This denser, cooler air sinks. An area of high pressure forms.
Air moves from a place with high pressure to a place with low pressure. The moving air is called wind. The name of a wind is the direction from which it comes. A north wind comes from the north and moves toward the south. Winds near the ocean are sometimes named differently, as you can see in the diagrams.
Land Breeze
A land breeze blows from the land toward the sea. At night, the water is warmer than the land. The air above the land is cooler, so it sinks. This creates high pressure at the surface of the land. The air above the land moves toward the water.
Sea Breeze
A sea breeze blows from the sea toward the land. During the day, the air above the land is warmer than air above the water. The air rises, creating low pressure at the surface of the land. The air above the water moves toward the land.
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As you go even higher, air pressure keeps decreasing.
Higher in the atmosphere the particles in the air can move farther apart. Air pressure is lower.
The air particles higher in the atmosphere squeeze the air particles at Earth's surface close together. Dense, closely packed particles exert greater pressure than loosely packed particles.
Lesson Checkpoint
1. What happens when water vapor cools?
2. What happens to air pressure as you go higher in the atmosphere?
3. Cause and Effect How do differences in air pressure cause wind?
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Lesson 3
What are air mass?
Air masses affect weather all the world. As they move, so does the type of weather they carry.