What are the main parts of a plant?
What All Living Things Need:
Living things have needs. Plants and animals need food, air, water, and space to live and grow.
Animals need to find food to eat. Plants are different. They can make their own food. Plants use energy from the Sun to make food.
Plants come in all sizes and shapes. They can grow almost anywhere. Each plant needs special things to grow. Most plants have four parts. Roots, a stem, flowers, and leaves are the four main parts.
Why Plants Need Leaves:
Plants need leaves to make food. The leaves make a type of sugar. A plant's leaves are a part of its leaf system. A system has parts that work together.
Carbon dioxide gas enters a plant through holes in the leaves. Water enters a plant through the roots and stem. Leaves also take in sunlight. Water and carbon dioxide are changed into sugar and oxygen. Energy from sunlight does this. The sugar is the plant's food. The oxygen goes out through holes in the leaves.
This is what a plant needs to make food.
Other Ways Leaves Help Plants:
Leaves also help a plant take in water. Leaves can let out extra water through tiny holes. A plant that lives in dry places may have fuzzy leaves. This helps keep water inside the plant.
Some leaves help keep the plant alive. Leaves can be tough or sharp.
They can be filled with poison. These leaves keep animals from eating them.
Why do plants need roots and stems?
How Roots Help Plants:
Roots hold plants in the ground. They store food for the plant. Roots draw water and minerals out of the soil.
Many plants have a taproot. Taproots are large roots that grow deep in the soil. They store food for the plant. Have you eaten a beet or a carrot? If so, you've tasted a taproot!
Beets and carrots are roots you can eat.
There are small root hairs at the tips of roots. Roots with their many hairs grow deep into the soil. These hairs take in water for the plant.
Tubes carry water to the stem and leaves. The Sun can dry out a plant. On hot days, roots take in water to replace what is lost.
Water moves from the root hairs into the root. Then it travels up to the stem and leaves.
How Stems Help Plants:
A stem holds up a plant's leaves, fruits, and flowers. Its tubes move water from the roots to the leaves. Others tubes take food from the leaves to the stem and roots.
Some stems are thin and grow along the ground. These stems can grow roots and a new plant.
Cactus stems are fat and have a thick covering.
This helps keep water inside the plant.
Potatoes are stem parts that grow underground. They store food for the plant. New stems can grow from a potato's buds. The buds are also called "eyes." Some stems have special parts that keep plants safe. Some stems have hairs that sting animals. Other stems have thorns. Both thorns and stinging hairs help keep animals away.
These cactus plants have thorns. The thorns are special leaves.
Potatoes can be eaten. But you must dig them out of the ground.
How are plants grouped?
Flowering Plants:
Grasses and trees are types of plants. Trees have a strong, woody stem to hold them up. Grasses do not have woody stems. They grow near the ground.
In the fall, many grasses keep only their roots alive. In the spring they grow a new stem with leaves.
In the fall many trees' leaves die and fall off. These trees are deciduous. Deciduous trees grow new leaves in the spring.
Making Seeds: 
Flowers have special parts that make pollen. The petals of a flower attract insects or other animals. They often move the pollen. Wind can also pollinate a flower. This happens when pollen is moved to the part of another flower that makes seeds. When a flower is pollinated, seeds form. Fruit grows around the seeds to protect them.
This bee moves pollen from another plant to the seed-making part of the flower.
Coniferous trees do not lose their leaves all at once. They do not grow flowers. They have cones that make seeds. The leaves of these trees look like needles. Pine, spruce, hemlock, and fir are coniferous trees.
Two Types of Cones: 
Coniferous trees make two kinds of cones. One cone is a small pollen cone. The other is a large seed cone. A seed starts to grow when pollen from the pollen cone of another tree attaches to the seed cone. Seeds fall to the ground when they are ripe. Sometimes the seeds grow into trees.
Pollen from these small cones needs to reach seeds in a bigger cone. Wind makes this happen.
How do new plants grow?
Scattering Seeds: 
Seeds are scattered so they can grow in new places. Some seeds are scattered by water. Wind can carry seeds that are very light. Animals carry other seeds away. Sometimes animals eat the seed's fruit. The seed passes through the animal's body. Then it is dropped to the ground. Other seeds are scattered when they stick to an animal's fur.
A seed can blow away in the wind.
Special Ways of Releasing Seeds: 
Some types of cones need to be heated by a forest fire. Then the cones can release their seeds. The fire also removes other plants around the trees. This makes space for the seeds to grow.
A seed can float away in water.
A seed can be eaten.
Germinating and Growing: 
Seeds come in different colors, sizes, and shapes. Every seed has a tiny plant inside it. Every seed also has a seed coat. This protects the plant inside the seed. The tiny plant can grow into a new plant.
Every seed has one or more seed leaves. A seed leaf gives food to the new plant.
Seeds need special things to sprout, or germinate. They need air, the right temperature, and enough water. When things are right, a seed sprouts. The seed breaks open and a seedling, or young plant, begins to grow. A young root grows down. A stem with leaves grows up. This plant uses food stored in its seed to grow.
This seedling has sprouted. It needs water and sunlight to grow.
Life Cycle of a Plant: 
First, a seed must germinate. Next, a seedling grows a root downward into the soil. Then, the seedling's stem grows upward. Then the stem grows leaves. Finally, the leaves use sunlight to make sugar for the plant to eat.
This peanut plant starts out as a seed. What happens next?
Soon the seedling grows into an adult plant with flowers. The flowers are pollinated and new seeds grow. If the seeds germinate they grow into new plants. Then the cycle starts again.
How are plants from the past like today's plants?
Plants That Lived Long Ago: 
A fossil is the remains of a living thing. Fossils come from plants or animals that lived long ago. We can learn about plants by studying fossils.
A fossil forms after a plant dies. The plant gets pressed into mud and rots away. The mud keeps the plant's form. Over time, the mud hardens into rock. When the rock cracks open, you can see the fossil.
Petrified fossils form when rock replaces plant parts. Sometimes a tree gets buried in the ground. Minerals from water replace the tree's wood. Over a long time, the wood becomes stone.
When a plant becomes extinct, none of its kind will ever live again. Ferns that live today are different from extinct ferns.
Plants Change Over Time: 
By studying fossils, we've learned that the first plants did not have flowers or cones. But plants changed over time. Trees that made cones spread over Earth. Plants with flowers started to grow.
Magnolias are flowering plants. They have grown and changed over millions of years. Magnolias from long ago kept their leaves year-round. Now, some magnolias lose their leaves in the fall. But magnolia flowers have stayed the same for millions of years.
Plants grow all over the Earth. They grow and live in different ways. Plants make food energy from light energy. Without them, life would be impossible!
Magnolia trees grew on Earth when dinosaurs lived here. Dinosaurs are extinct. Magnolia trees are still found on Earth.
What did you learn?
1. How do roots help a plant stay alive?
2. What are some different ways that seeds are scattered to make new plants?
3. How have plants changed over time?
4. In this book, you have read about pollination. Write to explain how petals help pollination. Use details from the book as you write.
5. How are deciduous and coniferous trees alike? How are they different?
How are animals grouped?
What All Animals Need: 
Almost all animals need water, food, oxygen, and shelter to live.
Animals get water from drinking or eating food. They get food by eating plants or other animals.
Animals get oxygen from air or water. Many land animals breathe with lungs. Many water animals breathe with gills.
Animals need shelter. Some animals find or build shelter. Other animals grow hard shells to protect themselves.
Ways of Grouping Animals: 
Animals can be grouped by their traits. A trait is the way an animal looks or acts. Animals get traits from their parents. Traits can be used to group animals.
Animals with Backbones: 
Animals with backbones belong to one group.
A vertebrate is an animal with a backbone. Vertebrates' backbones grow as they get older. Fish, snakes, and cats are all vertebrates. Vertebrates can look very different.
Fish are vertebrates that live in water. Fish have scaly skin. They breathe through gills.
Amphibians are vertebrates. They can live in water. They can also live on land. Amphibians breathe through gills when they are young. They also get oxygen through their skin. As they grow, they develop lungs. Toads and frogs are amphibians.
A frog is an amphibian.
Fish are vertebrates.
Reptiles are vertebrates with scaly skin. Crocodiles and alligators are reptiles. They breathe through lungs. Snakes, lizards, and turtles are reptiles too.
Birds are vertebrates that breathe through lungs. They have bills instead of teeth. Wings and light bones help most birds fly. Their feathers keep them warm.
Mammals are vertebrates. Mammals have hair on their bodies. This keeps them warm. They breathe through lungs. Mammals feed milk to their young.
Animals without Backbones
Most animals do not have backbones. These animals are called invertebrates.
Most invertebrates do not grow as big as vertebrates. Invertebrates make up most of the animals on Earth.
The body of this sea jelly is soft. Most of it is water.
A butterfly is an invertebrate.
There are many more invertebrates than vertebrates. Sea jellies, butterflies, and clams are all invertebrates.
Worms are invertebrates. They have long, soft bodies. Worms do not have legs. They slide and wiggle through the ground to move. Earthworms live in soil and keep it healthy.
Insects, spiders, and crabs are arthropods. Arthropods are the largest group of invertebrates.
They have skeletons on the outsides of their bodies. They also have legs with joints.
How do animals grow and change?
Life Cycles: 
All animals grow and change over time. These changes are called a life cycle. Animals start as an egg. Some animals lay their eggs. The eggs hatch when the young animals are ready. Other animals grow from eggs inside their mother's body. Those mothers give birth to live young. Some animals begin life looking like their parents. Others look different.
A Butterfly's Life Cycle: 
A butterfly begins life as an egg. A caterpillar, or larva, hatches from the egg. A larva is a young insect. The caterpillar eats and grows. Soon it spins a hard covering, or chrysalis, around itself. The larva is now a pupa. It grows and changes. It becomes an adult butterfly. The butterfly breaks open the chrysalis and crawls out. Butterflies lay eggs. After laying eggs, butterflies die. Then the life cycle of the butterfly is complete.
Some Vertebrate Life Cycles: 
Vertebrate life cycles can be different. Some vertebrates go through many changes as they grow. Others hardly change at all.
A Frog's Life Cycle: 
Frogs go through many changes. They start life in the water as eggs. Tadpoles hatch from the eggs. They breathe with gills and live underwater.
The tadpole grows lungs and legs, and turns into an adult.
Most adult frogs live near water.
A frog must change a lot before it looks like its parents.
A Mammal's Life Cycle: 
Most mammals develop inside their mother's body. Young mammals drink milk from their mothers. They have either hair or fur. Many young mammals look a lot like their parents soon after they are born.
This panda cub looks a lot like its parents.
How do adaptations help animals?
An adaptation is a trait that helps an animal meet its needs in the place where it lives. Adaptations are inherited; or passed on, from parents to their young.
A pelican is a bird that lives near water. It needs to swim to find food.
A pelican's webbed feet help it swim.
Its webbed feet are an adaptation.
A pelican has a special bill. It acts like a net to help the pelican catch fish.
Adaptations for Getting Food: 
Animals have many adaptations for getting food. An eagle's feet can hold food while it flies.
Deer have sharp front teeth to help cut plants. They also have flat back teeth to help grind plants.
A cardinal eats seeds. It uses its short, strong bill to break open the seeds. Each adaptation fits an animal's needs.
Warblers pick out insects.
Adaptations for Protection: 
All animals need ways to stay safe. Some animals can quickly run away from enemies.
Other animals are colored in a way that makes them hard to see. This is called camouflage. Camouflage helps some animals stay alive.
Some animals have spikes or horns for protection. The porcupine has hundreds of sharp quills. This adaptation is called armor.
Other animals mimic, or look like, a different animal. The king snake mimics the coral snake, which is poisonous. Other animals then avoid the king snake.
How have these animals protected themselves?
Behaviors That Help Animals: 
Behaviors are things that animals do. Some behaviors are inherited. Other behaviors that animals need are learned. These behaviors can be learned from parents or other animals. The ability to learn is inherited, however.
These geese are migrating.
These bats are hibernating.
A behavior an animal is born with is an instinct. Instincts help some animals survive during winter. Many animals know to migrate, or move long distances, to find more food.
Other animals know to hibernate or sleep, during winter. Their bodies slow down so they don't need much food.
Animals learn some behaviors by watching parents or other animals. Adult chimpanzees show their young how to find and get food. The young learn which foods are good to eat.
This young chimpanzee is learning how to find food.
How are animals from the past like today's animals?
Animals That Lived Long Ago: 
Signs of past life are called fossils. A fossil can be an animal track or print hardened into rock. This is called a fossil mold. A fossil mold can be filled with rock. Then it is called a cast.
Ancient Insects: 
Tiny insects caught in sticky tree sap have become fossils. Fossils of larger animals, such as saber-toothed tigers, have been found in tar pits.
How Animals Today Compare to Those of Long Ago: 
Fossils help people learn about animals and plants that lived long ago. They help us tell what Earth was like and how it has changed. Some animals that lived in the past are extinct. That means they no longer live on Earth.
Animals have found ways to live in many places on Earth. Their adaptations keep them alive. Animals have found incredible ways to keep living!
What did you learn?
1. What are animals that do not have backbones called?
2. Name two animals that are vertebrates.
3. What does camouflage do?
4. You have read about behaviors that help animals. Write to explain how an animal's instincts and learned behaviors affect its survival. Use examples from the book as you write.
5. Sequence Name the four steps of a butterfly's life cycle in order.
What are ecosystems?
Places for Living Things: 
A living thing needs just the right environment. An environment is everything around a living thing. Plants and animals are living things. They need sunlight, water, and soil. They also need the right kind of weather. Sunshine warms the environment. It helps plants make their own food.
Climate is also important for an environment. Climate is the weather a place has over many years Different environments have different climates.
Climate affects an environment's water and soil. Water and soil affect the plants in an environment. Plants need certain kinds of water and soil to live.
Plants and animals get what they need from where they live. They interact with nonliving things in an ecosystem. The parts of an ecosystem work together.
Redwood trees grow in a coastal ecosystem. Rain and fog from the ocean give them water.
The parts of this ecosystem need each other. Some birds find fish to eat in the ocean. Then they fly to the redwood trees to make nests.
These trees are part of a coastal ecosystem.
Special Homes: 
Plants and animals both need a place to live. This place is their habitat. They get what they need from their habitat. Plants get light, air, water, pollinators, and space to grow. Animals get food, water, and a space to live and grow.
If a part of a habitat is missing, the plants and animals can't live there. They might not get what they need to live. They might have to move to a new place.
Living things of one kind that live in the same place at the same time are a population. Southern California has many coyote populations. They live on brushy hillsides.
Squirrels live on the hillsides too. Coyotes hunt the squirrels. The coyotes, squirrels, and other living things in the ecosystem make up a community.
These two coyotes are part of a population.
Sometimes ecosystems change. First, one part of the ecosystem changes. This causes other parts to change.
If it rains a lot in Southern California, plants will grow more. Squirrels have more food to eat. The squirrel population increases.
More squirrels mean more food for coyotes.
The coyote population increases too.
Squirrels and coyotes are part of the community in this hillside ecosystem.
Which ecosystems have few trees?
Some places on Earth are warmer than other places. These places have less rain and fewer trees. Such places are called grasslands.
A grassland is a land ecosystem. It has many grasses and plants with flowers. Grasslands have cool or cold winters and hot summers. The summers are often dry. Grassland soil is also dry. It is too dry for trees to grow there.
Grassland plants have long roots. They can get water that soaks deep into the soil. Winter frost kills plant leaves. Roots store food to grow new leaves in spring. Grazing and fire kill leaves too. New leaves grow from the roots.
Some grasslands get more rain than others. Tall grasses grow there. Short grasses grow where there is less rainfall.
How much rain do you think this grassland gets?
A desert is a place that gets little rain. During the day, it is usually very hot. At night it is cool or even cold. Plants and animals that don't need much rain live there. Cactus plants can live in the desert. They store water in their stems.
Many desert animals hide during the hot day. Some stay in tunnels under the ground. Others rest under plants. Desert animals go looking for food at night, when it's cool. Snakes find and eat small animals. Bobcats hunt for birds and small animals to eat.
Tundra -- Land of Long Winters: 
The tundra is a place that is very cold and dry. It is near the North Pole. Tundra winters are long and cold. Tundra summers are short and cool. Tundra soil stays frozen underground all year.
Summer days in the tundra are very long. The Sun shines twenty-four hours a day on some parts of the tundra during summer. Winter days in the tundra are very short.
In some places, the Sun doesn't shine at all in the winter.
Trees can't grow in the tundra. Their roots can't grow in the frozen soil. Small plants, such as grasses and wildflowers, can grow there.
The snow melts during the tundra summer. It forms ponds. Birds make nests near the ponds. In the summer they find insects to eat. Most tundra birds fly to warmer places in the winter.
Why can't trees grow in the tundra?
A group of wolves is called a pack. Wolves hunt in the tundra in packs.
A group of caribou is called a herd. The herd stays together in the tundra.
What are some forest ecosystems?
Coniferous and Deciduous Forests
Coniferous forests grow where the winters are cold and snowy. Coniferous trees have leaves like needles. Spruce and pine trees are coniferous trees.
Most plants can't grow under conifer trees. Some animals can live under conifer trees. They can find food and shelter in the coniferous forest.
Deciduous forests grow where there are rainy summers and snowy winters. Oak and maple trees are deciduous. Deciduous trees drop their leaves in the fall.
More sunlight reaches down through deciduous forests. That allows plants to grow. Many animals can live in a deciduous forest. Insects and birds live in the plants and trees.
Tropical forests grow where it is warm all the time. These forests get lots of rain. Many tall trees grow in tropical forests. Little sunlight reaches the gound in tropical forests. Many plants grow on the tall trees so they can get sunlight. Most of the animals live in the trees too.
Birds and insects live in tropical forests. There are many different tropical forest insects. There are so many that we haven't named them all!
Tropical forests are full of amazing animals. One tropical forest in Brazil has beetles that don't live anywhere else. Some tropical forest spiders are big enough to eat birds!
What are water ecosystems?
Places that have fresh water include lakes, ponds, rivers, and streams. Lakes and ponds have land all around them. In rivers and streams the water moves Some of these places get fresh water from under the ground. Other places get water from rain or snow. Many plants and animals live in places with fresh water.
A wetland is low land that is covered with water. The water is there most of the year. But it is not very deep. Trees, grasses, and plants live in a wetland. Some of the animals that live there are fish, bears, and birds.
These animals live in wetlands. Manatees eat the plants that grow there. Alligators eat the fish and birds that live there.
Oceans contain salt water. Oceans are shallow near the land. Clams, crabs, and fish all live near the shore.
The water gets deeper as you move away from land. Fish, shrimp, and whales live in deeper water. Water far below the surface is dark and cold. No plants and few animals can live there.
Many rivers flow into the ocean. Fresh river water mixes with salty ocean water. When this happens, a salt marsh can form.
A salt marsh is a kind of wetland. Special plants and animals live in a salt marsh. They can live in water and soil that has salt. Many fish, crabs, and other animals are born in salt marshes.
Our Earth has many different ecosystems. Ecosystems are always changing. Ecosystems change when the climate changes. They change when animals move out of them or into them. They change in many ways.
Ecosystems give us and other living things everything needed to live! Without ecosystems, there could not be life.
What did you learn?
1. What do animals need from their habitat?
2. How do the plants in the grassland get water?
3. Which kinds of forests have trees that drop their leaves?
4. In this book you have read about what happens to coyote populations when it rains a lot in Southern California. Write to explain why there could be more coyotes when it rains, using what you have read.
5. What main idea did you learn about the tundra? What other details did you learn about the tundra?
How do living things interact?
Ways Living Things Interact: 
Living things interact in many ways. An interaction between them can be helpful. It may help a living thing survive. Animals living in groups help each other. One kind of living thing may help another. Two different kinds of living things may help each other.
Think about these examples. Many animals live together in herds. The animals of the herd protect each other. Flowers need light to grow. Sometimes flowers grow on trees. Then they can get more light. Insects drink nectar from flowers. When they do this, they spread the flowers' pollen to other flowers.
Members of a herd protect each other.
A tree helps a flower get light.
An insect gets nectar.
It spreads the plant's pollen.
Living in Groups: 
Some plants and animals live in groups. Members of the group protect each other from predators.
For example, prairie dogs live in groups. A prairie dog whistles if it senses danger, such as a predator. This tells the whole group of prairie dogs to run and hide. They stay hidden until the danger is gone.
These fish live in a group. How do you think the fish help each other?
Sometimes an interaction helps only one thing.
A barnacle is a small animal. It attaches to the skin of a whale. As the whale swims, the barnacle opens its shell to catch food. The whale helps the barnacle get food. But the barnacle does not help the whale in any way.
In some interactions, different kinds of living things are partners. They help each other.
The yucca moth helps the yucca plant. The moth moves pollen from one yucca to another.
The plant also helps the moth. It gives the moth a place to lay its eggs. It also gives the moth food for its young.
How do living things get energy?
A living thing that makes its own food is a producer. All green plants are producers. They make food by using energy from sunlight. They also use matter from air and soil.
Some living things cannot make their own food. They get energy from the food they eat. A living thing that eats food is a consumer.
Sunlight gives an ecosystem all its energy.
This cattail is a producer. This crayfish is a consumer. 
Do you know which of these animals is an omnivore? The bear! A wolf eats only meat.
It's a carnivore. Sheep are herbivores. They eat only plants.
Kinds of Consumers: 
A consumer that eats only plants is an herbivore. A consumer that eats only animals is a carnivore. Some consumers eat both plants and animals. This type of consumer is an omnivore.
Food Chains: 
The cattail, crayfish, and raccoon make up a food chain. A food chain is a group of producers and consumers that interact. The crayfish eats the cattail.
It gets food energy from the plant. Then the crayfish becomes prey for the raccoon. Prey is any animal that others hunt for food. An animal that hunts food is a predator. Energy moves from producers to prey to predators. Each organism gives off some of this energy as heat.
Two or more food chains make a food web. Energy moves in many different ways in a food web. A Great Plains food web is pictured below.
When one part of a food web changes, other parts change. What would happen if prairie dogs were removed from the web? Ferrets would not have enough food. They would start to die out. Animals that eat ferrets would have to find other food. This could affect the mouse population.
How do living things compete?
Competing for Resources: 
When two or more living things need the same resource, they are in competition. Living things compete for food, water, sunlight, and living space.
Predators and Prey: 
Groups of predators compete for prey. Hunting birds are one example. Faster, stronger birds may catch more prey or steal prey from other birds.
Prey also compete. A strong deer has a better chance of escaping a predator.
What are these animals competing for?
Other Kinds of Competition: 
Living things compete for space. Purple loosestrife is a plant that takes space from other plants in many places. Some animals compete with humans for space.
Living things also compete for oxygen. Sometimes too many algae grow in a pond, lowering oxygen levels. Animals must compete for the oxygen left.
Competition can follow a cycle. The amount of food can affect a population of animals. The population, then, can affect the amount of food. The cycle begins again.
How do environments change?
Causes of Change: 
Living things can change their environment. A beaver builds a dam across a stream. The dam floods many dry places. It forms a wetland. Fish and birds can live in the wetland. But animals who lived on the dry land must move. Those animals must find new homes. Some may not survive.
How is this beaver changing the environment?
Natural events such as droughts, hurricanes, and floods, can also change environments. Little rain falls during a drought. Plants and animals may not get enough water during droughts. Hurricanes can wash away beaches, knock trees over, and cause flooding.
A flood can kill plants, spread mud, move good soils, and destroy animals' homes.
In 1980 the volcano Mt. St. Helens erupted in the state of Washington. The blast knocked down and burned trees. It sent mud and rocks sliding. Few living things survived in the area of the eruption.
Over time, wind carried seeds to Mt. St. Helens. New plants grew. Animals returned. Today Mt. St. Helens is filled with life. But the mountain could erupt again.
Forest fires can destroy habitats in the same way. Forest fires may also improve habitats for existing plants and animals.
Mt. St. Helens changed the environment. But living things returned.
Patterns of Change: 
Living things change together. Often the changes happen in patterns. For example, trees grow old, die, and fall. Decomposers feed on the dead trees. A decomposer is a living thing that breaks down living things that have died. This is called decay. Decay can make the soil good for growing new trees. These trees will die someday and decay also. The life cycles of the two different trees are connected.
What is a healthy environment for people?
What People Need: 
People need many things to live. They get these things from the environment.
People need food. Most people buy their food.
It comes from farms and ranches.
People need shelter. Shelter protects people from the weather.
People need clean water. Many people get their water from special lakes. These lakes are called reservoirs.
Do you know where your food and water come from?
People need air. The air is often cleaner outside cities.
People need a clean environment. To keep it clean, waste must be removed. Garbage and other waste go to different places. Some towns and cities put garbage in a landfill.
Healthful Foods: 
Eating healthful foods helps people get all the vitamins, minerals, and other nutrients their bodies need.
Look at the picture below. It shows some of the foods that your body needs, such as fruit, vegetables, dairy food, and fish. You should also eat whole grains, nuts, eggs, and meat. Food should be fresh, clean, and stored properly.
Is this the kind of food you eat?
From Food to Energy: 
When you eat food, your digestive system goes to work. It breaks food down. It turns food into a form your body can use.
Look at the drawing. It shows the main parts of the digestive system. They turn food you eat into energy you need to live and grow!
Food is crushed in your mouth and then mixed with digestive juices in your stomach. Your small intestine does most digesting. It also moves particles into your blood. The large intestine removes food you cannot use.
How can people stay healthy?
Exercise, like healthful foods, builds healthy bodies. People get exercise in different ways. They may swim or skate. They may clean the house or rake the yard.
Exercise helps keep your heart, lungs, and muscles strong. These are important parts of your body's systems.
Exercise keeps people in shape. People who are in shape have more energy. They can work and play. They can feel good about themselves.
It's important to try to stay healthy. You can stay healthy by eating good foods. You can also stay healthy by getting enough exercise and rest.
What is your favorite kind of exercise?
Have you ever had the flu? The flu is an illness caused by germs.
Germs are very small living things or particles. Viruses and bacteria are germs. Many germs can cause disease. A disease is when your body or part of your body does not work properly.
Most illnesses are not dangerous. Still, it's better to be healthy than to be sick!
A microscope can be used to observe very small things.
Stopping the Spread of Germs: 
You can do many things to stop the spread of germs. Just follow these simple rules. First, stay home from school when you are ill. Second, wash your hands often. Third, cover your nose and mouth when you sneeze or cough. Fourth, clean and cover all cuts and scrapes.
What did you learn?
1. Give examples of how animals interact in a helpful way and a harmful way.
2. What do living things compete for?
3. What are two natural events that can change environments?
4. In this hook you have read about staying healthy. Write to explain three ways people can stay healthy. Use examples from the book as you write.
5. If you knew one part of a food chain was missing, what conclusion could you make?
Why is water important?
Living things need water. Trees and snails need water to grow. Green plants must have water to make food. Fish need the oxygen in water.
Your body needs water. Water makes up about two-thirds of your body. Water helps you in many ways. Water helps digest food. It carries things to and from parts of your body.
Your body uses water to change its temperature. When it's cold, water keeps you warm. When you are hot, you might sweat. Sweat is a kind of water.
It carries heat away from you.
Some animals live only in water. You can see many of these animals with your own eyes. Others are tiny. You can't see those animals without help.
The Uses of Water: 
We use water for many things. People get food from oceans, rivers, and lakes. Farmers use water for their crops. This water comes from the sky or moves through pipes.
People need to drink water. Animals need to drink water too. Water is also used to clean food and buildings.
We use water to make electricity. Running water turns wheels. These wheels make power we can use. The power travels through wires to our homes.
We use water to travel. Ships carry goods we use across water. We even play in and around the water.
Water is used in many factories.
The Planet of Water: 
Earth is called the "blue planet." Three-fourths of its surface is covered with water.
Most of Earth's water is salty. Salt water makes up Earth's oceans. Some of the salt comes from rocks. Some salt also washes off the land. This salt mixes with the water.
Why is Earth called the "blue planet"?
Salt in ocean water affects our ability to use it. You can't water plants with ocean water. You can't drink it either. Factories can't use ocean water to make things.
Water is found in many places. Some water is in the ground. Some is frozen. A small amount of water in the air is called water vapor. Water vapor is an invisible gas. It rises from surface water and mixes with air.
Fresh Water: 
We need to drink fresh water. Fresh water contains little salt. We could not live without it. A small part of Earth's water is fresh. Most fresh water is frozen.
We get some fresh water from underground. Water goes down into the soil. Water that collects in between rocks is called groundwater. People dig wells to get this water.
Most fresh water is frozen in ice near the North and South Poles.
Many streams and rivers have fresh water. This water is always moving. Streams form rivers. Both streams and rivers can flow into lakes. Wetlands form when water gathers on low land. The water stays there for part of the year.
Wetlands are home to many animals. They also soak up extra water. This helps to stop flooding. The water in wetlands goes down into the soil. Then it becomes groundwater.
This stream might flow into a river or a lake.
How do forms of water change?
Forms Water Can Have: 
Water can freeze during cold weather. In some places, it stays below 0 degrees Celsius all year. This means it stays below freezing all year.
The weather is cold for only part of the year in other places. There, cold weather in the winter freezes the water. Later, warm weather turns the water back into liquid form.
Water can become a gas. Evaporation is what happens when water turns into a gas. Energy from the Sun heats water. It becomes water vapor. You cannot see water vapor. On hot days you can sometimes feel sweat on your skin. Sweat evaporates unless there is too much water vapor in the air.
Water vapor can turn back into a liquid. Condensation is what happens when water vapor turns back into liquid water. During the night, air cools. Water vapor turns into drops of water. These drops of water are dew.
How Does Water Move Around Earth?
Water on Earth is used over and over. Water moves from Earth's surface into the air. Then it returns to Earth again. This is called the water cycle. This cycle gives us fresh water.
Water vapor rises into the air. The cooler air causes it to condense and turn into water droplets or ice particles. These droplets collect and form clouds.
Precipitation can fall as snow.
When water particles in clouds grow, they fall faster. Water falling to Earth is called precipitation. Water falls to Earth as rain, snow, sleet, or hail depending on the temperature.
Some precipitation goes into the ground and becomes groundwater. Some runs into oceans, lakes, rivers, and streams. Surface water later evaporates.
The water cycle continues all the time.
Ways to Clean Water: 
People need clean water. Water may have germs.
It may have salt, dirt, or other things in it. All of this is taken out of the water we use.
Germs in water can make people feel sick. We want to drink water that tastes good. Salt or dirt in water can break machines too.
This water-cleaning plant is in Chicago, Illinois. It is one of the largest in the world.
How does water get cleaned? First, it goes to a water-cleaning plant. Chemicals are sometimes added to kill germs. Sometimes the water sits in big tanks. This lets dirt sink to the bottom. Finally, water is pumped through a filter. Now, the water is clean and can be used!
Water is everywhere. People and animals need water to live. We use water for many things. Without water, there wouldn't be life on Earth!
What did you learn?
1. Where can fresh water be found on Earth?
2. Name the different forms of precipitation.
3. How much of Earth's surface is covered by water?
4. In this book you have read about how water is cleaned. Write to explain how water is made safe for drinking. Use details from the book in your answer.
5. What causes condensation to happen at night?
What makes up weather?
Parts of Weather: 
Weather is what the air is like outside. The air temperature is part of the weather. So is the water in the air. The wind speed and kinds of clouds are part of the weather too.
Most clouds are made of water droplets. Clouds hang in the air. When a cloud can't hold any more water, it rains. Puffy, white clouds usually mean good weather. Dark clouds often bring rain.
Measuring Weather: You might say that the weather is hot today. But your friend might disagree. To your friend, the weather might not feel hot. So scientists use tools to measure the weather. That way, we know exactly what the weather is like!
Earth has a blanket of air around it. That blanket is called the atmosphere.
It contains gases that have no color, taste, or odor. The atmosphere has weight. It presses down on Earth. How much it presses down is called air pressure. High air pressure is caused by the atmosphere pressing down more. Low air pressure is caused by the atmosphere pressing down less.
The atmosphere has many parts. Weather happens in the lower part. Planes often fly above the weather.
Changes in air pressure lead to changes in the weather. Scientists use a tool called a barometer to measure air pressure.
High air pressure means good weather is coming or is here. The skies are clear or will be clearing. Low air pressure often means bad weather. The weather is cloudy or rainy or will be cloudy or rainy. Storms happen during low air pressure.
A hygrometer measures the air's water vapor, or humidity. High humidity causes damp, wet air. Low humidity causes dry air.
A rain gauge shows how much rain has fallen. An anemometer tells the speed of the wind. Wind vanes tell the direction of the wind.
All these tools help scientists learn more about weather. They also help scientists predict what the weather will be like.
Weather tools give scientists data, or facts. Scientists use the data to make weather maps. The maps show temperatures, air pressure, and storms. Look closely at the weather map below. Do you see the key? The key's pictures help you better understand the weather.
This weather map uses pictures to show what the weather is like. What is the weather like in Atlanta, Georgia?
Weather satellites move around Earth and take pictures. They send the pictures back to Earth. Scientists study the pictures. The pictures help scientists tell which way storms are moving. This helps scientists talk about the weather.
Cars, trucks, and factories can pollute the air in cities. The pollution they make is a gas, called exhaust. The exhaust moves into the air. The exhaust can hang over the city. The Sun's rays can turn the exhaust into smog and ozone.
Weather scientists make pollution alerts when there's smog or ozone in the air. The alerts warn people to stay inside because smog or ozone can be harmful to health.
How are weather patterns different?
Weather changes follow patterns. The same weather happens over and over again. Weather patterns depend on the Sun, water, and where you live. People near the ocean have one kind of weather. People far from the ocean have another kind of weather.
The coast along the state of Washington has rainy winters. The Cascade Mountains, near the middle of the state, have snowy winters. And the eastern section of Washington has dry, cold winters.
Eastern Washington State does not get much rain or snow.
I It rains on the coast because the air is warm and wet. The rain turns to snow in the mountains because the air is colder there. And the mountains block rain and snow from going past them.
Each kind of desert has its own weather pattern. The Sonoran Desert in Southern Arizona and California has a hot, dry summer season. But storms come with heavy rain. The rain is due to moist air from the Gulf of California. Saguaro cactus take in the rain and save it for later.
Dangerous Storms: 
Some storms only bring rain. Thunderstorms can be dangerous. Lightning can strike people, trees, and buildings, so people should find shelter.
A hurricane is a huge storm. It starts out over an ocean. It has very strong winds. When it hits the land it causes great damage. People usually know about hurricanes before they happen.
A hurricane can cause heavy rain and huge waves.
A tornado is a spinning column of air that touches the ground. Tornadoes form below thunderstorm clouds. They are smaller than hurricanes. But their winds are much stronger. Tornados form quickly. When a tornado is spotted, people must go to a safe place.
Heavy rains or big waves can cause flooding. Flooding can make roads dangerous to travel on.
People usually know about flooding beforehand and move to higher ground.
A blizzard is a winter storm. Blizzards have very cold air and a lot of snow. Strong winds blow the snow. It is dangerous to be out in a blizzard. Blizzards can trap people in the snow. They can also make people too cold. It is important to stay indoors during blizzards in order to be safe.
These students are sent home from school during a blizzard.
The National Weather Service warns people about storms. A storm watch means that a storm could be happening soon. A storm warning means that a storm is about to happen or is already happening.
Different kinds of weather happen every day. It is difficult to figure out why certain weather happens.
But tools help scientists understand the weather!
What did you learn?
1. What are some qualities that weather has?
2. Name three weather tools that help to measure weather. Tell what each tool does.
3. What do high air pressure and low air pressure tell us about the weather?
4. In this book you have read about the pollution that happens in cities. Write to explain how pollution forms. Use examples from the book.
5. Make Inferences: Why do you think the coast of the state of Washington gets wet weather in the winter, while the Cascade Mountains in the middle of the state get snow?
How do rocks form?
Rock is found in nature. Rock is solid. It is nonliving matter. All rocks are made of one or more minerals. A mineral is a natural material that forms from nonliving matter.
You can tell rocks apart by their properties. Physical properties are what we see by looking at a rock. These properties include the rock's color, the minerals in the rock, and the texture.
Rocks can be many different colors. The texture of the rock is the size of the bits of minerals that make up the rock. Is it smooth to touch? Is it rough? Does it feel scratchy? Does it feel hard or soft? The grains of the minerals that make up the rock determine how it feels. In some rocks the bits of minerals are so small you can't see them easily.
Rocks are put into three different groups.
Igneous rock forms from minerals and gases melted together. Sometimes this mixture cools slowly and hardens below ground. Then the mineral grains may be easy to see. Other times, the red-hot mixture cools quickly above ground, or in the ocean. Then the mineral grains may be too small to see.
Sediment is material that settles to the bottom of rivers, lakes, and oceans. Little bits of rock make up sediment. After a very long time, layers of these bits of rock pile up and stick together. Over time, the layers get pressed together, and they form sedimentary rock. Sedimentary rock forms in layers. It forms one layer at a time.
Fossil remains can be found in sedimentary rocks. Extinct plants and animals were buried in sand and mud. This hardened into rock. Layers of rocks with fossils show the history of life.
The word metamorphic means "to change form." Metamorphic rock is rock that is changed by heat, pressure, or both into another kind of rock. Shale is a sedimentary rock. When shale gets buried deep underground, heat and pressure change its minerals. The shale becomes slate, a metamorphic rock.
What are minerals?
Identifying Minerals: 
Color is a property of minerals. Some minerals come in many different colors. Quartz can be pink, purple, yellow, brown, white, or black. Some minerals only come in one color.
Scientists use many tests to help identify minerals. Rub a mineral across a rough surface.
It may leave a streak mark or powder. Even if a mineral comes in different colors, it will always leave the same color streak mark.
Minerals also have luster. This property shows how a mineral reflects light.
Another test to identify minerals checks their hardness. The hardest mineral is diamond. No mineral can scratch it except another diamond.
Some minerals can be identified by how they look. Gold sometimes comes in nuggets. Other minerals can be identified by how they feel, smell, or taste.
How We Use Minerals: 
Every day we use minerals. Most toothpaste contains fluoride that helps fight cavities. Fluoride comes from the mineral fluorite. The windows in your house are made from the minerals quartz, soda, ash, and limestone. The salt in your food is the mineral halite. The fork and spoon you eat with are made from minerals. We use minerals for almost everything.
Minerals Keep Us Healthy: 
Our bodies need minerals to stay healthy. Minerals help form bones and skin. Minerals also help release energy and move it through our bodies.
Many of the minerals we need are found in plants. Green leafy vegetables, such as spinach, contain calcium. Iron is found in fruit and green vegetables. Sodium is a mineral found in celery. Potassium is found in fruits. Phosphorus is found in green beans. Minerals are in almost everything we eat.
Why is soil important?
Soil is a thin layer of loose material. It covers most of Earth's land. Soil takes a long time to develop. It has the material plants need to grow.
Soil is more than just bits of rock. It holds water. It holds material that was once living.
Living things in soil break down what is left of plants and animals after they die. This process is called decay. Decay releases nutrients into the soil.
Some minerals release nutrients too. Plants need nutrients to grow.
Earthworms mix up the topsoil as they dig through it. That improves the soil.
We depend on topsoil to grow our food.
Soil must pack down hard and stay firm so that houses built on it don't shift.
Soil has three different layers. The layers are topsoil, subsoil, and bedrock. The layers may look different in different places.
Topsoil is the first layer. It has rock pieces mixed with decayed parts of plant and animal remains. The decayed remains are called humus. Humus has a lot of what plants need to grow.
Subsoil is the soil under topsoil. It is lighter in color. It has less humus. It has pieces of broken rocks. The roots of trees grow down into subsoil. Water from rain may soak down into this layer.
As this rock breaks down, it slowly turns into new soil over many, many years.
Soils can be different. Sand, silt, and clay particles are found in soil. Sand particles are the largest. They have large spaces between them. Water runs quickly through sandy soil. Silt has medium-sized particles. Its spaces are not as large as those in sand. Silty soil holds water well. Clay particles are the smallest. Once clay soil gets wet, the particles hold tightly together.
All soil has the same four ingredients. Most of the soil is made up of weathered rocks. These rocks have minerals. Humus makes up soil too. It is a very important part of soil. Air and water fill in the spaces between rocks and humus.
Loam is a good soil for growing plants. It contains sand, silt, clay, humus, and air. Plants can soak up water easily from loam.
Wet clay feels smooth and sticky.
What did you learn?
How are metamorphic rocks formed?
Name some different ways minerals are used.
What are the three layers of soil?
In this book you have read about minerals. Write to explain how scientists identify minerals. Use details from the book.
5. Compare and Contrast Compare and contrast ways igneous rock forms and the effects these ways have on the rock.
What are Earth's layers?
Earth's Layers
Earth is divided into three layers. The crust is the outer layer of Earth. It is made up of different kinds of rock. The thickness of the crust is different in different places. The crust is about 37 kilometers (23 miles) thick under the continents. Compare Earth to a peach. The crust would be the skin of the peach.
The mantle is below the crust. It is made up of very hot rocks. It can flow like thick toothpaste.
The core is the innermost layer of Earth. It is made up of metal. The core is so hot that it could melt. But it is packed tightly together and stays mostly solid. Its outer part is a very hot liquid.
Shapes on Earth's Surface: 
A landform is a solid feature on Earth's crust. Mountains, hills, and valleys, are landforms. Other features include bodies of water. There are many different types of landforms on Earth.
Forces shape these landforms. Moving water is a strong force. Rivers can act as saws. Sand and pebbles in the water slowly cut through rock. Flooding rivers leave silt, sand, and pebbles on their banks. These things help form valleys.
A glacier is a moving body of ice. It slowly moves downhill. A volcano is an opening in Earth's crust. Hot, melted rock is forced through it. Some mountains form when pieces of rock are pushed along cracks in Earth's crust. A lake forms when water flows slowly enough to fill up an area.
This picture shows a mountain, a kind of landform, and a lake.
What are volcanoes and earthquakes?
How Do Volcanoes Form?
Volcanoes start in the mantle. This is where magma forms. Magma is hot, partly melted rock that is under pressure from gases it contains. This pressure forces it up through Earth's crust. The hot material erupts through an opening in a volcano.
Lava is the material that erupts from a volcano. Lava has ash, cinders, and hot rock in it. As lava cools, it becomes new crust.
This lava was once magma inside Earth.
Magma collects in large pockets. These pockets are called magma chambers. As magma leaves a chamber, it moves up a tunnel or vent. Sometimes magma escapes and erupts from a side vent. But most magma erupts through a central vent. It erupts through a bowl-shaped crater at the top of the volcano.
Parts of Earth's crust can shift suddenly. This causes the ground to vibrate. This shaking is called an earthquake. Most earthquakes begin along a fault.
A fault is a large crack in Earth's crust.
Earthquake vibrations move as waves through Earth. They also move up and down. The waves can cause cracks. They can pile up rubble in areas around the parts of the crust that moved.
Earthquake Damage: 
How much earthquake damage occurs depends on how long the crust shakes. It also depends on how close the earthquake is to the surface. Earthquakes can happen very close to a city. This causes a lot of damage to buildings, bridges, pipes, and roads.
An earthquake can cause landslides. Landslides are downhill movements of rocks and earth. Landslides can happen on the land or the ocean floor. Landslides underwater can cause huge waves. Landslides on the land can bury large areas.
What are weathering and erosion?
Landforms are always changing. This happens when rocks in landforms break apart. Weathering is any action that breaks rocks into smaller pieces.
Weathering goes on all the time. It causes changes over time. Some changes might take a year. Others could take hundreds of years.
Plants can cause weathering. Their roots grow into rocks. As the roots grow, they break apart rocks.
Water mixed with decayed material in soil can also cause weathering. This water changes the minerals in the rock. The rock grows weak and starts to break apart. Water can also seep in and freeze in the cracks of a rock. Then the water expands.
Ice pushes against the rock and breaks it apart over time.
Ice changes rocks in a different way. Glaciers are huge bodies of ice. Rocks and ice scrape against the ground as a glacier moves. This makes valleys wide and smooth. Rocks of all sizes drop to the ground when the glacier melts. These rocks and soil line the edges where the glacier used to be.
Look at how weathering has broken down this boulder into smaller and smaller pieces.
Erosion
Sometimes weathered materials are picked up and carried away. The movement of weathered materials is called erosion. Glaciers, gravity, wind, and water can cause erosion.
Water erosion is the most common form. Rivers move bits of rock. During floods, mud and sand flow over a river's banks. Rainwater washes soil away from hills.
Erosion can make new islands. Rivers carry rocks and soil to the ocean. They build up over time into islands. Then wind and waves change their shape.
In dry places such as deserts, wind often causes erosion. Wind can pick up dry sand and soil. It blows them to other places since there aren't many plants to hold them down. The particles bump into rocks and cause small grains to break off. Slowly the rocks change.
Living things can cause erosion. Some squirrels tunnel through soil. Worms can mix and carry soil to new places. Groups of ants move soil to make nests. When an animal tunnels, it allows water and air into the ground. Then the air and water continue the erosion.
Erosion caused the hole in this cliff.
Gravity causes erosion by pulling rocks downhill. This material moves slowly unless the slope is steep. Weathered material moves very quickly on steep slopes! The movement of wet soil is called a mudflow. When rocks slide quickly down a hill, it is called a rockslide.
What did you learn?
1. What forces can cause erosion?
2. Name the different layers of Earth.
3. How do volcanoes erupt?
In this book you have read about how weathering affects landforms. Write to explain how weathering can change landforms. Use examples from the book to support your answer.
5. What happens during an earthquake?
What are resources?
Everything we need comes from natural resources. A natural resource is any useful material that comes from Earth. Natural resources are important because living things need them.
Some resources can be replaced. Trees that grow in soil are a good example. People cut down trees for wood. Wood is used to build new houses. Wood chips can be turned into pulp to make paper.
When trees are cut down, we can plant new ones to replace them. After a short time these new trees will be tall enough to cut down. A resource that can be replaced in a short time is called a renewable resource.
Many natural resources are hidden deep underground. Miners have to dig up rocks called ores. Ores contain metals or minerals that people use.
Steel is made from iron. Many things are made of steel, such as forks and buses. There is a limited amount of iron ore underground. It cannot be replaced. A nonrenewable resource is a resource that cannot be replaced.
Hematite is an ore that contains the metal iron. Iron is used to make steel.
Coal, oil, and natural gas are also nonrenewable resources. They are fuels that release energy when burned. When we use up the natural resources in one area, we need to find new places to dig for them.
An Endless Supply of Resources: Some natural resources will never be used up. We have an ongoing supply of sunlight, air, and water. These resources are always available on Earth.
Mining can permanently change the Earth's surface. This open-pit mine is an example.
How can we protect our resources?
Using Resources Responsibly: 
People can save fuel in different ways. They can walk, ride a bicycle, or take a bus. When people buy products with less packaging, they are saving paper and plastic. These are ways to conserve. Conservation is using natural resources in a way that does not waste them or use them up.
Clean water is a resource we can conserve by using less of it. For example, when you are brushing your teeth, you can turn the water off.
To conserve water, many communities clean used water. To do this, they pipe dirty water into a wetland. Soil in the wetland pulls out harmful particles. Next, plants and tiny living things destroy the particles. Then, the cleaned water flows back into a river. Now, people can use it again.
Soil must be used wisely too. Some farmers plant crops around hills. If the crops were planted up and down the hills, water could wash away the soil. Farmers also plant trees around their fields to keep soil from blowing away.
Cities are growing. So people build on farmland.
The soil is then lost to farming. How can we protect farmland for future generations?
We could allow these leaves to decay. They would turn into compost. Compost can add nutrients to soil.
Using Up Land Space for Trash: 
We throw away things we no longer need. Then a truck moves our trash to a landfill. Trash is buried in landfills. The trash never really goes away. Landfills are filling up quickly.
We can reduce the space we need for landfills. One way is to burn garbage in special furnaces. But then smoke from the burning must be cleaned. It can harm the air we breathe. We can also make less trash.
What are ways to use resources again?
You conserve resources when you reuse things. Cloth napkins and empty jars can be reused. You can also give away your old clothes for others to use.
These are everyday objects. Can you think of some ways to use these materials again?
Another way to conserve resources is by recycling. When you recycle something, it is changed so that it can be used again. Useful resources can be made into new products. We use recycled metal, glass, plastic, and paper all the time.
This bench is made of recycled plastic.
Glass is often recycled. At the recycling plant, glass is sorted by color. Next, it is broken into pieces called shards. They are shipped to glass companies.
At the glass companies, the shards pass under a magnet to remove metal caps and rings. Shards are crushed into small particles called cullet. Cullet is cleaned, dried, and melted in furnaces. This glass can now be made into bottles, jars, or windowpanes. Recycled glass can be used over and over.
Reusing and recycling are not new. Your great-grandparents may have bought flour in cloth sacks. Then they may have reused the cloth for rags, towels, or clothes. People have been recycling for years.
Today, it is easy to recycle. Many towns collect items to be recycled. Movie theaters and office buildings have special containers for bottles and cans. Grocery stores collect used shopping bags to be recycled.
This wall was made by reusing materials such as old tires and aluminum cans.
Conservation includes using products made from recycled materials. Sleeping bags you buy can have stuffing made out of shredded plastic bottles. Or you can buy a sweater with yarn recycled from old clothing.
There is an easy way to remember how to protect our natural resources. Remember the three R's -- reduce, reuse, and recycle.
What did you learn?
What are three examples of nonrenewable resources?
How can farmers conserve soil?
Why is it easy to recycle today?
In this book, you read about landfills and the need to reduce, reuse, and recycle our resources. Write to explain how reducing, reusing, and recycling would affect our landfills. Use examples from the book to support your answer.
How are renewable resources similar to nonrenewable resources? How are they different?
How can we describe matter?
All of the things you see around you are made of matter. Matter is anything that takes up space and has mass. You can sense the mass of an object by how heavy it feels. You can see that air takes up space when you blow up a balloon.
A property is something about matter that you can see, hear, touch, or smell. A ball looks round. It feels smooth or bumpy. It can be hard or soft. It makes a sound when you bounce it. You can smell a flower to learn about its properties.
Nearly all matter is a solid, a liquid, or a gas. Each kind of matter is made of very tiny particles. The particles are so small that we cannot see them. The particles are always moving. In some kinds of matter, they move a little. In other kinds of matter, they move a lot.
A bowling ball is a solid. Like other solids, it keeps its shape. It stays round. In a solid, all the tiny particles are packed tightly together. They jiggle very fast, but they stay in place.
Orange juice is a liquid. It takes the shape of the glass it is in. It will take a new shape if poured into a different glass. The particles of liquids are loosely connected. The particles can flow past one another. What if you poured the juice into a new container? It will still take up the same amount of space.
Gases do not have a shape. Air is a gas. Tiny gas particles are not connected to each other. They bounce off each other as they move freely in space. Unlike solids and liquids, the amount of space that air takes up can change.
When air is pumped into a ball, it expands. It pushes against the inside of the ball. This pushing is called pressure. The air particles get more tightly pressed together as you pump more air in.
What happens if you break a chunk of gold into smaller pieces? Each particle of gold is still the matter gold. Gold is an element. An element is matter made of a single type of particle too small to see.
Most matter is made out of many types of particles. The smallest particle of an element that has all the properties of that element is an atom. Gold is made up only of atoms of gold. Clay is an example of matter made Periodic Table of Elements up of different kinds of atoms.
Atoms act together to give matter its properties.
Scientists have done experiments to find out how many different elements there are in matter. Their experiments show that there are more than one hundred different elements. Scientists list all these elements in a table. It is called the periodic table of elements. The elements are placed on the table near other elements with the same properties.
How are properties of matter measured?
Tools for Measuring Mass: 
One property of matter that you can measure is mass. Mass is the amount of matter an object has. A balance measures mass. The metric units for measuring mass are grams (g) and kilograms (kg). One kilogram has 1,000 grams.
An object's mass is the same no matter where it is. But the weight of an object can be different in different places. Things have different weights on Earth than they do on the Moon. A scale is used to measure weight.
Tools for Measuring Volume: 
Another property of matter you can measure is volume. The volume of an object is the amount of space that the object takes up. You use a measuring cup or graduated cylinder to measure the volume of liquids.
The metric unit for measuring the volume of a liquid is the liter (L). We can also measure small amounts of liquid in milliliters. One liter has 1,000 milliliters.
The volume of the milk in this jug is about 2L.
The volume of orange juice in this bottle is about 1L.
Solids have volume, just as liquids do. To measure the volume of a solid, fill a measuring cup half full of water. Record the measurement. Now, place a rock into the water. The water rises because the rock has volume. It takes up space. Look at the water level now. Record the new measurement. Subtract the first measurement from the second. The difference in the water levels is the volume of the rock.
The volume of the water in this measuring cup is 500 mL.
Density is a measure of the amount of matter in a certain amount of space. A bowling ball and a rubberball have about the same volume. But the bowling ball has more mass and greater density.
You can study the density of matter by watching how an object floats. How well an object floats in a liquid or a gas is called buoyancy. Stones have little buoyancy in water. They sink because they have a higher density than water. A helium balloon has lots of buoyancy in air. It rises because helium has a lower density than air.
Tools for Measuring Other Properties:
Size is another property that can be measured. The distance from one end of something to the other is its length. The basic unit for measuring length is the meter (m). We use millimeters (mm) and centimeters (cm) to measure small things. One meter is 100 cm or 1,000 mm. We use kilometers (km) to measure long distances. One kilometer is 1,000 meters.
A cubic unit is a cube used to measure volume of a solid. A cube that is 1 centimeter on all sides has the volume of 1 cubic centimeter. To find the volume of a box, put cubes of the same size into the box, and fill it. The volume of the box is a measurement of how many cubic units it takes to fill the box.
Some objects are too small to see easily. Use a magnifying glass to make things look larger. Then you can see their properties better.
What did you learn?
How can you show that air has volume and takes up space?
How are the particles of a solid different than particles of a liquid or a gas?
Where would you look to find out if something is an element?
In his book you read about measuring volume. Write to explain how you would measure the volume of a trunk. Include details from the book.
5. What property causes an object to float? Describe the effect of this property.
What are physical changes in matter?
Workers are carving this mountain into a statue of the Native American leader Crazy Horse. They must blast away and hammer bits of rock to do this.
The workers are causing a physical change to the mountain. A physical change is when matter changes the way it looks but does not become a new kind of matter. This mountain looks different. Its shape has changed. But it is still a solid mountain.
Some Ways to Cause Physical Change: 
The clothes and paper in these pictures have gone through physical changes. The clothes were folded.
The paper was cut.
One kind of physical change is when matter changes form, or state. States of matter are the different forms matter can have. They are solid, liquid, and gas. The state of matter can change. But the kind of matter stays the same.
Folding clothes causes a physical change.
Cutting paper causes a physical change.
Water can change its state of matter. Freeze a cup of water. It turns into ice. It changed from a liquid to a solid. The state changed, but the kind of matter did not. Water and ice are the same kind of matter. If you melt the ice, it is still water. Its state changed from a solid back to a liquid.
This water is a solid.
This water is a liquid.
Changes in temperature can cause matter to change its state. If you boil water, its state changes.
It evaporates. That means it changes into a gas called water vapor. A physical change takes place. The gas is still a form of water. But you cannot see it. The water particles are far apart in the air. The water has changed state. But it has not become a new kind of matter.
Ice is water in a solid state. It can change to a liquid. Hold an ice cube in your fist. The particles in a solid vibrate in place. The heat from your hand changes it. The heat makes the particles slide past one another. You feel water drip from your hand. A physical change takes place. But the kind of matter is still the same.
What are some ways to combine matter?
Each coin you see below is made up of matter. Putting different coins together makes up a mixture. A mixture is made of two or more kinds of matter that are placed together. There can be different amounts of each kind of matter in a mixture.
In mixtures, the matter does not change into new matter. You can separate each kind of matter from the others.
How many of each type of coin make up this mixture?
A magnet can help separate this mixture of sand and iron.
Some mixtures are very easy to separate. The coins are easy to separate. A strainer can help separate some mixtures. The bigger matter stays in the strainer. The smaller matter passes through the holes. A sand and iron mixture is harder to separate. A magnet can pull the iron out. The sand is left behind.
A strainer helps separate the parts of this marble and sand mixture.
Mix lemonade powder and water together. The lemonade powder will look as if it has disappeared. But it is still there. Its particles have just become too small for you to see. The powder has dissolved, or broken down, in the water. It is now a solution. A solution forms when one or more substances dissolve in another. It is a kind of mixture. You cannot see the powder. But you know it is there when you taste the lemonade.
There are many kinds of solutions. Soda is a solution. Carbon dioxide gas and other substances are dissolved in water to make soda.
This glass of lemonade is a solution.
The carbon dioxide gas dissolved in this soda is escaping.
Solutions can be separated since they are mixtures. Salt dissolves in water. You can separate this mixture if you boil the salt water. The water evaporates. The salt is left.
Both the lemonade and the salt dissolved in water. But even these changes are just physical changes. The kind of matter in each solution is still the same.
Straining doesn't separate the salt from salt water.
What are chemical changes in matter?
Have you ever watched bread being made? It starts as a mixture. Flour, water, baking powder, and other ingredients are mixed in a bowl. After it is baked, you have bread. Baking the bread in an oven causes a chemical change. During a chemical change, one kind of matter changes into a different kind of matter. The heat of the oven causes a new substance to form. Bread is the result.
Baking bread causes a chemical change.
Chemical changes can happen quickly or slowly. Fire changes paper or wood into ashes. It takes only minutes. Rust forms on an iron chain very slowly over time. The iron changes into rust. A new kind of matter forms.
You cannot often get the original matter back after it has gone through a chemical change. You cannot easily change the rust back into iron. You cannot change the ashes back into paper. You cannot change bread back into its ingredients.
Burning is a fast chemical change.
We use chemical changes every day. When we eat food, chemical changes take place. As the food moves through your body, it changes. It gives your body energy. It helps you grow.
Cars burn gasoline when they run. The chemical change sends energy through the car engine.
Chemical changes help make things easier to do. Soap causes chemical changes that remove stains.
Another chemical change lets you use your CD player. You push the buttons to play it. Chemicals combine inside the batteries. New substances form. A small amount of electricity is produced. Now you can hear your favorite music.
Matter can change in many ways. It can change states. It can be combined in different ways. These changes make many things possible.
What did you learn?
1. What are three states of matter?
2. Why is cutting paper a physical change?
3. Is a salad a mixture? Why or why not?
4. In this book you read about dissolving salt in water. Write to explain why it is a mixture and how you could demonstrate this. Use details from the book as you write.
5. What causes water to turn into ice? What is the effect on the state of matter?
What happens when things change position?
Suppose you spin a top. You can tell it moves because its location changes. It starts in your hand. Then it spins across the ground. If an object is in a new location, its position has changed.
The top is in motion as its position changes. A top also has circular motion. This means it moves in circles around a central point.
Ways of Looking at an Object's Position: 
The position, direction, and movement of an object depend on how you look at it. For example, as you walk down a hall, a water fountain may be in front of you. After you walk by it, it is behind you. As you keep walking, the fountain seems to be moving away.
A map can help you locate things. A map shows the position of objects in relation to each other. Look at the path on the map above. Tell how you would get from the classroom to the lunch room. Use position words like forward, left, right, and behind to explain your trip.
When one thing depends on another thing for its meaning, we say it is relative. Relative position is the position of one object compared with the position of other objects. Look at car 64 below. Its relative position is in front of the other cars. Another car might be leading the race. Then you would say car 64 is behind the lead car. The relative position of car 64 changes depending on the position of other cars.
Look at the train below. The locomotive is in front. Two cars are being pulled behind it. Could the cars move in front of the locomotive? They could if the train started moving backward. Relative position can change if objects start moving in a new direction.
How Fast Things Move: Speed is how fast an object changes its position. Speed can be fast. A jet plane moves fast. Speed can be slow. Honey moves slowly. Some things have such a slow speed that you can't see them move!
Constant Speed: Objects can move at a constant speed. This means that they do not change how fast or slow they move.
They are always changing position. The rate at which they change position stays the same.
Variable Speed: Bumper cars move at a variable speed. An object moving at a variable speed changes speed as it moves. Bumper cars can speed up, slow down, or stop.
How does force affect motion?
The Causes of Motion: 
A force is any push or pull. A force can change an object's position. It can change the direction of an object's motion too.
Most forces you use are contact forces. To push or pull an object, you must touch it. A bat makes contact with a ball to move it.
The more force you use, the more an object's motion changes. The harder you push on a cart, the faster it goes!
The mass of an object affects how it moves. You don't need much force to begin pushing an empty cart. When the cart is full of food, it has more mass. Now more force is needed to begin moving the cart.
As the cart moves, its wheels rub against the floor. This causes friction. Friction is a contact force that slows an object's motion. Smooth surfaces produce less friction than rough ones. Friction is helpful when you want to slow something down.
More force is needed to push three carts than to push just one.
Motion and Combined Forces: 
You know that pushes, pulls, and friction can change an object's motion. Now think about the forces in tug-of-war. Your team's pull is a force in one direction. The other team's pull is a force in the other direction. If the forces are the same, the rope doesn't move.
Suppose everyone on your team pulls together to move the rope. The rope will move in your direction if you have the stronger force. So get more friends to help!
Lots of forces cause a bike to change its motion. You push on the pedals. You push on the handlebars and shift your weight to turn. Friction between the tires and the ground slows your forward motion. Going up hills takes more force. You may gain too much speed going down hills. You pull on the brakes to slow down. All these forces work together to keep your bike moving.
Gravity and Magnetism: 
A non-contact force is a push or pull that affects an object without touching it. Gravity is a non-contact force that pulls objects toward each other. Gravity pulls everything on Earth toward Earth's center.
Weight is the amount that gravity pulls on an object. Objects weigh less on the Moon because the Moon has less gravity than Earth. The pull of gravity is less the farther you are from the center of Earth.
You weigh less on top of a mountain than you do at its base.
The pull of gravity also depends on matter. Objects with more matter have more mass. The more mass, the stronger the pull of gravity.
Magnetism is another non-contact force. Magnets pull on objects with certain kinds of metal such as iron in them. You might use a magnet to pull a steel paper clip across your desk. Steel is a metal with iron in it. Magnets do not affect objects that lack these metals.
This magnet does not attract crayons since they lack metal the magnet can attract.
How do simple machines affect work?
In science, work means using force that moves an object. You do work when you rake leaves or kick a ball. How much work you do depends on how much force you use. It also depends on how far you move an object.
Work is NOT done if an object does not move. Try pushing a big snowball. If the snowball does not move, no work is done. You may be using force, but you are not doing work.
How much work do you do in a day? To find out, you would have to keep track of all the pushing and pulling you do. Then you would have to see how far those pushes and pulls moved things.
Putting a book on a shelf is work. What if you put the book on a shelf twice as high? You would do twice as much work! You would also do twice as much work if you put a book that weighed twice as much on the lower shelf.
Some Simple Machines: 
Machines can't reduce the amount of work that needs to be done. But they can help make your work easier. Here are six kinds of simple machines.
Inclined Plane: 
Look at the man pushing the cart below. Without the ramp, the man would have to lift the cart into the truck. That would take a lot of effort. He is using a machine called an inclined plane. An inclined plane, or ramp, is a slanting surface. It connects a low spot to a higher one. The mover pushes with less force, but he must push for a longer distance. The same amount of work gets done, but with less effort.
A wedge is a simple machine. It is used to split, cut, or fasten things. A wedge has one or two slanted sides that form a sharp edge. A wedge can move through material and separate it. A knife is a wedge that can cut a pie. An axe head is a wedge that can split wood.
A screw is an inclined plane wrapped around a center post. The spiral slide in the picture looks like a big screw.
Screws are used to hold things together. They are used to raise and lower things too. The lid on a jar is a screw. The lid raises as you open the jar. The lid lowers as you close the jar.
A lever is another simple machine. A lever is a bar that rests on a support. Levers lift and move things.
A seesaw is a lever. Push down on one side of a seesaw. Then watch the person on the other side go up!
Whenever you open a door, you use a simple machine. It is called a wheel and axle. The doorknob is a wheel. The post that attaches to its center is an axle. Turning the knob takes less force than turning the small axle with your fingers. Since the knob is larger, however, you must turn it a longer distance.
The rides you see below both use a big wheel and axle. Instead of turning the wheel, a motor in these rides turns the axle. The motor turns the axle a small distance. But the distance the axle turns the wheel is great. This makes the ride fun. The motor must put a great force on the axle to do this.
Do you think the people on this ride are having fun?
Pulleys are simple machines that can help move things in the right direction. The sails of a boat are attached to pulleys. A pulley has a wheel that turns on an axle. The sailors pull on a rope that wraps over the wheel of each pulley. This causes the sail to move in the proper direction.
You live in a world of motion. Look around. What is moving quickly? What is moving slowly? What simple machines will you use today to make moving things easier?
What did you learn?
What is the difference between constant speed and variable speed?
Would it take more force to begin moving an empty wagon or a wagon loaded with pumpkins? Why?
What is the difference between a contact force and a non-contact force? Give examples of each.
In this book you have read about work and simple machines. Write to explain how simple machines make work easier without lessening the amount of work that gets done. Use examples from the book.
Summarize the forces used when riding a bike.
What is energy?
Energy is the ability to do work or cause change. Work is when force causes an object to move. Most of our energy comes from the Sun. The Sun heats Earth. The Sun's light energy makes plants grow.
We use many other forms of energy too. Sound energy comes from a CD player. Chemical energy runs a car's engine. Electrical energy runs many things in this kitchen.
Stored energy is potential energy. It can change into another kind of energy to do work or cause a change.
Fuel, such as natural gas, has potential energy.
Long ago, plants made food using energy from the Sun. The plants died and turned into fossils that are used as fuel. When we burn this fuel, we free potential energy. Work is possible.
When you use batteries, you release potential energy. The stored energy in food, fuels, and batteries is chemical energy.
Potential energy can change to kinetic energy. Kinetic energy is the energy of motion. A car burns gas. The potential energy stored in the gas changes to kinetic energy. The car moves.
A skier rests at the top of a hill. He has potential energy. Then he slides down the hill. His potential energy changes to kinetic energy.
A skier uses a lot of energy. But he can replace it by eating food. The gas a car burns to create energy cannot be easily replaced. "Fossil" fuels, such as gas, are not renewable.
How does energy change form?
Energy changes from one form to another all the time. Your body stores potential energy in the form of chemical energy. This chemical energy changes to kinetic energy when you move.
The kinetic energy of your arm cannot make a light bulb burn bright. But it can be used to flip a light switch. This changes electrical energy to light energy. But not all the energy gets changed. Some energy is given off as heat. The light bulb gets hot.
People use machines to change forms of energy too. An electric toothbrush sits in a base that plugs into an electric outlet. The toothbrush's battery stores electrical energy as chemical energy. The chemical energy changes to electrical energy when you turn on the toothbrush. The electrical energy then changes to mechanical energy as the toothbrush moves.
This energy holds the particles of matter, such as food, together. That's why eating food gives us energy.
This is the energy of moving things. Moving parts of machines have this kind of energy.
This energy can pass through metal wires. We use this kind of energy to run appliances.
We see the Sun's energy in this form. Plants use light to make food. We change other forms of energy into light so we can see.
This energy makes particles of matter move faster. We feel this energy as heat.
Energy can move from one place to another.
A moving object, such as a ball, has energy. You can feel the energy when you catch the ball.
Energy can also travel as waves. The waves are shaped similar to the waves on a moving rope. Look at the rope on the next page. It is moving from side to side. Energy makes this happen. It moves from one end of the rope to the other.
Light and other forms of kinetic energy move as waves. Bigger waves carry more energy.
Ocean waves carry energy.
How much energy does a wave have? How far the wave is from its midpoint shows its energy. You measure the distance from the midpoint of the wave to the high or low point of the wave. The top of a wave is called a crest. The bottom is called a trough. Wide waves have lots of energy. Narrow waves have less energy.
You should also look at the length of a wave. The wavelength can be the measurement from the top of one crest to the top of the next crest. Short waves have more energy. Long waves have less energy.
What is heat energy?
Matter is made up of moving particles. Particles move because they have energy. The energy of moving particles in matter is called thermal energy.
Thermal energy moves as heat. It moves from hot things to cool things. Put a spoon into a hot drink. Heat from the drink moves through the cool spoon. Soon the spoon is as warm as the drink. The flow of energy stops when the drink and spoon are the same temperature.
Heat is given off when energy changes from one form to another. The burner under the pot below changes electrical energy to heat. A burning match changes chemical energy to heat.
Try rubbing your hands together. The friction caused by rubbing gives off heat. There is heat every time energy moves.
A burning match is very hot!
Heat moves from the water to the frozen vegetables.
Heat energy affects matter. You can measure the effect of heat on matter.
Look at the ice a few times during the hour. Measure and record the amount of ice that has melted. Record the time when all the ice has melted. Record the temperature. Time is one way to measure how this heat energy changed the ice.
Water evaporates if more heat is added to it. The water turns into a gas called water vapor. Liquid water changes in another way at 100C (212F). Heat makes the water boil. The water takes up more space when it boils. Then it evaporates and becomes a gas. Hot bubbles of gas float to the top of the water. Hot water droplets called steam come out of the bubbles.
This water is boiling. Some of the water is leaving as steam.
What is light energy?
Most energy comes from the Sun. The Sun's energy reaches Earth as waves. The waves have different amounts of energy. Some of these waves affect us. We can see and use light energy.
Chemical changes also make light. Gas in the lamp below gives off light as it burns. The fish below gives off light too. Chemical changes in the fish's body make light.
Electricity gives us light. It makes the wire in a light bulb hot. The hot wire glows and gives off light. Most things that give off light give off heat too.
Light moves in all directions from where it starts.
It moves away from its source in straight lines. Light moves this way until an object stops it. Light cannot go around objects. Objects that get in the way of light's path cause shadows.
How Light Changes: 
Not all objects block light. Light can pass through some things, such as a window.
All objects reflect light. This means light bounces off the object and moves in a different direction. Some things, such as a lake, reflect light better than other things. Why? They have flat and smooth surfaces. This makes the reflected light move in the same direction.
Mountains and trees are reflected in this lake.
Look closely at the picture below. The drops of water refract, or bend, light. This makes the light change direction. This can change the way things look. Each drop of water refracts light from the flower. Little pictures of the flower form as the light bends.
Light passes through things at different speeds. This causes the light to refract. Light moves more slowly in water than air. The straw in the glass below looks broken because the water slows down and bends the light.
Refraction can cause light to separate. When this happens you can see a rainbow. A rainbow shows the many colors of light.
Light is made of many colors. When light hits objects, they absorb some of the light. To absorb means to take in. The rest of the light is reflected. Things absorb and reflect different colors of light. If something looks white, it is reflecting all the colors of sunlight. If something looks black, it is absorbing all the colors of sunlight. Absorbed sunlight often turns to heat. This is why dark objects feel warm in sunlight.
Green light has changed this white chicken to a green chicken.
What is electrical energy?
Matter is made up of particles that have electric charges. An electric charge is a small bit of energy. An electric charge can be positive or negative. Matter with mostly negative charges has a negative charge. Matter with mostly positive charges has a positive charge. Matter with the same number of negative and positive charges has no charge.
This balloon has no charge. It does not attract any pieces of paper.
Positive and negative charges attract. The negative charge moves toward the positive charge. You may get a shock when you touch a person. If so, negative charges jumped between the two of you.
The attraction between opposite charges can make things stick together. That's why paper sometimes sticks to a balloon.
The same charges repel each other. Objects with the same charge push each other away.
This balloon has a charge.
It attracts pieces of paper with an opposite charge.
Electric Currents and Circuits
Electric current is the movement of electrical energy or electric charge from place to place. Lightning is an electric current that moves in any direction. Electric current must follow a path to be useful. Electric current can make lights and CD players work. The path that a controlled electric current flows through is an electric circuit. Energy cannot flow if the path, or circuit, is broken. Look at the picture below. The switch must be closed for the electricity to flow.
Electricity flows through the circuit to light the light bulb when the switch is closed.
We need to make a lot of electricity because we use it every day. We have learned how to change energy into electricity. We can change the energy of moving water into electricity. We can change the energy of burning coal into electricity. We can turn the energy of heat and sunlight into electricity. What would modern life be like without electricity?
What did you learn?
1. What kind of energy is stored in a battery?
2. While running in place, the chemical energy stored in your body would change to what kind of energy?
3. Why does rubbing a balloon attract pieces of paper?
4. In this book you have read about thermal energy. Write to explain how thermal energy moves. Use examples from the book in your answer.
5. What is the main idea of the last paragraph on page 2? What details support it?
What causes sounds?
Take a walk in the city. Cities are noisy. Car horns honk. Buses and garbage trucks roar by. People talk on the street. It is much quieter in the country. Birds chirp. Cows moo. Water trickles in a creek.
Sounds are everywhere. Some sounds you hear may hurt your ears. You may like other sounds. Each sound you hear is different. Sounds are also alike in some ways.
Sound happens when matter moves back and forth very quickly. This movement is called a vibration. There must be movement to make sound.
The instruments pictured make sounds. They can make high sounds. They can make low sounds. Pitch is how high or low a sound is. Objects that vibrate slowly make a low-pitched sound. Objects that vibrate quickly make sounds that have a higher pitch.
Some instruments make sounds when you hit them. They are called percussion instruments. Drums are percussion instruments. Drums are played with rubber hammers, wooden sticks, brushes, or your hands. If you tap a drum lightly, you hear a soft sound. Hitting the drum harder makes a stronger vibration. This makes a louder sound.
Stringed instruments are played in two ways. You can pluck the strings. Or you can rub a bow across them. Both ways make sounds. The strings are different sizes. They can be long or short and thick or thin. Some are stretched tighter than others. Long, thick strings make a lower-pitched sound. Short, thin, tight strings make faster vibrations. They make higher-pitched sounds.
Using Air to Make Sound: 
The sound of your voice is made by vibrations in your windpipes. When air from your lungs passes between your vocal cords, they vibrate. You can speak and sing because your vocal cords vibrate. When you speak, your cords tighten. The tighter they get, the higher the pitch of your voice.
Your vocal cords are two pairs of thin tissue in your windpipe.
A wind instrument's sound comes from vibrating air inside it. Blow into a trumpet. Your lips vibrate against the mouthpiece as you blow. This makes the air inside the trumpet vibrate. It also makes sound.
You can change the pitch of the trumpet's sound in two ways. Change how your lips vibrate. Or press on the valves of the trumpet. Pressing on the valves changes how long the air column is inside the trumpet.
Do you know how to play a trumpet?
Some wind instruments use reeds. A reed is a thin piece of wood. It is attached to the mouthpiece. When a person blows on a reed, it vibrates. The vibration makes the air inside the wind instrument vibrate.
The vibrating air makes a sound. If you press the keys of the wind instrument, you can change the pitch of the sound.
How does sound travel?
What are sound waves?
A bell rings. Its vibrations move in the air. Some air particles are spread out. Others are squeezed together. The particles take turns doing this. This allows the bell's vibrations to move between these particles. This movement makes a wave called a compression wave. Sound waves are compression waves.
Sound travels as waves in the air.
Sound waves travel through matter. Some of the particles that make up matter get squeezed. Other particles are spread apart. The particles of matter take turns being squeezed and spread out. The length of a sound wave can be measured. We measure from the center of one squeezed area to the center of the next.
Sound waves from a jackhammer have lots of energy. If you were standing nearby, you would hear a very loud sound. Sound waves lose energy as they move away. Farther away, the sound would not be as loud.
You hear sound only when it travels through matter. Sound can travel through solids, liquids, and gases. The speed of a sound wave is different in each kind of matter.
The gases of air have particles that are far apart. Sound travels slowly through gases. Liquid particles are closer together. Sound travels more quickly through a liquid than a gas. Solid particles are closer together than gases or liquids. Sound travels fastest through solids.
Light travels faster than sound. That is why you may see fireworks before you hear them.
Echoes are sound waves that hit something and bounce back. Scientists use sound waves and echoes to study the ocean. A ship sends out a sound wave. When the sound wave hits the bottom of the ocean, it bounces back. Scientists measure how long the sound wave takes to bounce back. Then they can figure out how deep the ocean is at that spot.
Sound travels at about 1,530 meters per second in water. Some whales can make sounds that can be heard up to 160 kilometers away.
We hear sounds with our ears. The outer ear catches sound waves. The waves travel inside the ear to the eardrum. When the sound waves hit the eardrum, they make it vibrate. The vibrating eardrum makes little bones vibrate. The little bones touch the shell-like inner ear. It is filled with liquid and tiny hairs. The vibrating little bones make the tiny hairs move. The hairs are connected to nerves. The nerves carry signals to the brain. The brain recognizes the signals. Then we know what we are hearing.
Many animals have vocal cords like people do. They make sounds when their vocal cords vibrate. Dogs bark. Cows moo. Some animals make sounds that do not use vocal cords. Bees and mosquitoes make buzzing sounds when their wings vibrate.
Bats send out sounds people cannot hear. The sounds are high-pitched and bounce off insects. The sounds return to the bats' ears. This helps the bats find their food.
Chimpanzees grunt, bark, squeak, scream, and even laugh.
What did you learn?
1. How is sound made?
2. Describe the two ways stringed instruments are played.
3. Explain how your ears help you hear.
4. In this book you have read about vocal cords and the pitch of your voice. Write to explain how their relationship works.
Use details from the book.
5. How do people make sounds? How do animals make sounds? Compare and contrast the ways people and animals make sounds.
What are some patterns that repeat every day?
The Sun is always in the sky. You can see it on sunny days. It is there on cloudy days too. The Sun is a star. A star is a big ball of hot, glowing gases. Light and heat on Earth's surface come from the Sun.
Earth is small compared to the Sun. But they are both shaped like a ball. Earth does not make its own light. The side of Earth facing the Sun is lit by sunlight. The side of Earth facing away from the Sun is dark.
Earth is moving all the time. It spins around an imaginary line called an axis.
One end of this line passes through the North Pole. The other end passes through the South Pole. Earth spins on its axis in a counterclockwise direction. This is the opposite direction of the way hands on a clock move.
The Sun is at its highest point in the sky at around noon.
The Sun appears to move lower in the western sky as Earth rotates.
Earth makes one full spin on its axis every 24 hours. This is called a rotation. During this time, half of Earth faces the Sun. It is daytime there. The other half of Earth has night.
Earth always rotates at the same speed. During the year, some days have more sunlight than others. The number of hours of sunlight and darkness changes. But the total hours of sunlight and darkness in a day always add up to 24 hours.
The Sun may trick you. It appears to rise in the east. Then the Sun seems to move across the sky and set in the west. But the Sun is not moving at all! It only appears to move. It is really Earth that is moving.
Have you ever stood in the shade of a tree? If so, you were really standing in a shadow. A shadow forms when an object blocks the light that hits it. The shadow is cast onto a surface. It is shaped like the object that blocks the light.
The length and direction of shadows change. Find the shadow in the top picture. The Sun appeared in the east. The shadow is long. It stretches in the opposite direction from the Sun. Morning shadows stretch toward the west.
Find the shadow in the middle picture. At noon, the Sun is high in the sky. Shadows are short.
Later in the day, shadows become longer again. Afternoon shadows stretch toward the east. You can see this in the bottom picture.
Once the Sun disappears, there is no light to make shadows.
How do the length and direction of the shadow cast by this basketball hoop change during the day?
What patterns repeat every year?
Earth turns on its axis. Earth's axis is not straight up and down. It is tilted. Earth also moves, or revolves, around the Sun. In one year, Earth moves all the way around the Sun. This trip is called a As Earth moves, its axis always points in the same direction.
The northern half of V Earth tilts toward the Sun. This half gets more sunlight than the southern half. It is summer in the northern half. It is winter in the southern half.
Sometimes the northern half of Earth tilts toward the Sun. At other times the southern half tilts toward it. The part tilted toward the Sun gets the most direct sunlight. This part gets the most heat. It also gets more hours of daylight than darkness in a day.
The four seasons are spring, summer, fall, and winter. Which one do you like best?
The amount of sunlight changes from season to season. So do temperatures. These changes happen in patterns. Temperatures are often hot in the summer. In winter, temperatures are usually cold.
Think about December. The northern half of Earth is tilted away from the Sun. This means it gets less sun. Temperatures are cold. There are fewer hours of daylight.
Earth's tilted axis causes the Sun's position in the sky to change.
In different seasons, the Sun's place in the sky changes. This is due to Earth's tilted axis. The Sun is higher in the sky in summer. The Sun is lower in the sky in winter.
In spring and fall, Earth's axis is not pointed toward the Sun or away from it. Temperatures are not as cold as winter. But they are not as hot as summer. The hours of daylight and darkness are about the same each day.
Why does the Moon's shape change?
The Moon rotates and revolves like Earth. The Moon rotates on its axis. It revolves around Earth. The Moon takes about 27 days to make one rotation.
The Moon makes one revolution in almost the same amount of time.
The Moon rotates on its axis and revolves around Earth in about the same amount of time.
The closest natural object to Earth is 384,000 kilometers (239,000 miles) away. It is the Moon. At night, the Moon is very bright. But the Moon does not make its own light. Light from the Sun shines on the Moon and bounces off.
You can see the Moon sometimes during the day. This is because daytime light in the air is less bright.
We always see the same side of the Moon from Earth. No one saw the other side until a spacecraft took pictures of it in 1959!
The Moon and the Sun: 
Sometimes the Moon looks like a circle. At other times you cannot see the Moon at all. Between these times you can only see part of the Moon. This pattern of changes is the same. It starts over about every four weeks or 29 days.
Each different way that the Moon looks is called a You see more of the Moon each night until the phase called a full Moon. Then you start to see less of the Moon. Soon you cannot see the Moon at all. This phase is called a new Moon.
Half of the Moon is always lighted. We cannot always see this half. We see different amounts of the lighted half as the Moon and Earth move.
A lunar eclipse is caused by the Moon moving behind Earth. When it does, Earth blocks sunlight from reflecting off the Moon. During a lunar eclipse, Earth's shadow covers the whole Moon.
Earth makes a shadow on the Moon during a lunar eclipse.
Stars and the Telescope: 
Suppose you are looking at the night sky. Do you see stars? Stars may look small. But they are far away. Some stars are bigger than the Sun! Others are smaller. The stars that are very far away can be hard to see. There are tools to help you see these stars.
A telescope magnifies faraway objects as binoculars do. Both tools make objects look bigger. Then the objects are easier to see.
There are different kinds of telescopes. Some use tubes, mirrors that reflect light, and lenses that bend light. These parts let lots of light into the telescope. This makes objects in the sky easy to see.
There are even telescopes that do not collect light waves. They collect different waves instead. Some collect radio waves!
Patterns of Stars: 
Some stars seem to be in groups. These groups make patterns. A group of stars that make a pattern is called a constellation.
See how the lines connect stars together in two groups below? One looks like a big cup. It is part of a larger constellation. The other looks like a little cup. Its stars make up a second constellation.
Long ago, people saw many shapes in star patterns. They saw objects, animals, and people. They made up stories about what they saw. They gave these constellations names that we still use today.
The stars in a constellation look close together. But they are very far apart. What if you looked at the same stars from faraway in deep outer space? You would see different patterns.
Like the Sun, stars seem to move across the sky. But the stars really do not move. It just looks that way. This is because Earth is rotating on its axis.
Star patterns change with the seasons. As Earth moves around the Sun, constellations are in different places in the sky.
Look at the sky tonight. You might see the Moon. What phase is it in? Can you see any stars? What about constellations? The sky has many patterns. It is fun to learn about the patterns and watch them.
What did you learn?
1. Why does the Sun look larger than the rest of the stars in the sky?
2. When are shadows shortest during the day? Explain your answer.
3. What is the phase of the Moon called when it looks like a big circle?
4. In this book you have read about the four seasons. Write to explain why the seasons change. Use details from the book.
5. Explain the phases of the Moon in order.
What are the parts of the solar system?
Hot, glowing gases called plasma make up the Sun. It is the closest star to Earth. It looks brighter and larger than any other stars you see at night. That is because it is closer to Earth.
The Sun is huge. It is wider than the length of 15,000,000 football fields. The Sun is so large, one million Earths could fit inside it.
The Sun's temperature is 5,500C on the surface.
Its gas particles are tightly packed together. This gives it lots of energy. Some of the Sun's energy travels through space as sunlight.
How Objects In the Solar System Move: 
You live on Earth. Earth is one of nine planets. A planet is a large body that revolves, or travels, around the Sun. Many planets have moons. The Sun, all the planets and their moons, and other objects that revolve around the Sun make up the solar system.
The path an object travels as it revolves around the Sun is its orbit. The Sun's gravity keeps planets in their orbits.
Mercury is about 58 million kilometers from the Sun.
Mars is about 228 million kilometers from the Sun.
Venus is about 108 million kilometers from the Sun.
Most asteroids orbit the Sun between Mars and Jupiter.
The nine planets are divided into two groups called the inner and the outer planets. The four inner planets are Mercury, Venus, Earth, and Mars. They are close to the Sun. The outer planets are Jupiter, Saturn, Uranus, Neptune, and Pluto. They are farther from the Sun.
Thousands of rocky objects called asteroids orbit the Sun too. Asteroids are chunks of rock of different sizes.
In this diagram, sizes and distances are not true to scale.
What are the planets?
Mercury, Venus, Earth, and Mars are the inner planets. They are alike in some ways. They are rocky planets. They are closest to the Sun. They are also different in some ways.
Mercury has many craters. It is dry and very hot. It is the closest planet to the Sun. Mercury is the second-smallest planet. It is less than half the size of Earth.
It rotates, or turns once on its axis, in 59 Earth days.
It takes 88 Earth days to revolve around the Sun. Mercury has no moons.
It is easy to see Mercury's craters because it has no atmosphere.
Venus is also very hot and rocky. Its surface has craters, mountains, and valleys. It has an atmosphere. Thick clouds cover Venus and trap heat, which keeps it hot. It takes 225 Earth days to go around the Sun.
It rotates, or turns, once in 243 Earth days. It is larger than Mercury. Venus has no moons.
Venus is shown here without its atmosphere.
Earth is the third planet from the Sun. It is a bit larger than Venus. The time Earth takes to revolve around the Sun equals one Earth year. One Earth year is 365 1/4 days. One Earth day is equal to the amount of time it takes to rotate on its axis. One Earth day lasts 24 hours. Earth has one moon that is called the Moon.
Mars is the fourth planet from the Sun. It is called the "red planet." It has a reddish-orange, rocky, and dusty surface. Mars has volcanoes and deep canyons. It is smaller than Earth, about half its size. It takes 687 Earth days to revolve around the Sun. It only takes 25 Earth hours to rotate. It has two moons.
Earth is very different from the other planets. Earth has large areas of blue water, white clouds, white ice caps, and solid continents.
Earth is the only planet in the solar system that supports a wide variety of living things. Mild temperatures and plenty of water make life possible. The atmosphere has the right mix of oxygen and carbon dioxide for living things to breathe. The atmosphere also takes in most of the Sun's rays that can harm living things.
Most of Earth's energy comes from the Sun. But only about half of the Sun's light reaches Earth's surface. The atmosphere absorbs some of the light. More is reflected off clouds. Gases in the atmosphere scatter much of the reflected light. This makes the sky look blue.
Earth is made up of giant sections, or plates. These plates move all the time. Volcanoes and earthquakes can happen where the plates touch. Movements of the plates change Earth's surface.
The outer planets are much farther apart than the inner planets. Most outer planets are huge. Most are made up mainly of gas. They do not have solid surfaces.
Jupiter is the largest planet. It is more than 11 times bigger than Earth. It takes almost 12 Earth years to revolve around the Sun. But it rotates in only 10 Earth hours. It has bands of clouds, strong winds, and storms. Jupiter has more than 60 moons. Jupiter's rings are hard to see.
The sixth planet from the Sun is Saturn. It is the second-largest planet. Saturn is known for its rings. They are made up of chunks of ice and rock. The rings circle Saturn. Saturn takes 29 Earth years to revolve around the Sun. But it rotates in just 10 Earth hours. Saturn has at least 30 moons.
Uranus and Neptune are also gas giants. Pluto is the only outer planet not made up of gas.
The seventh planet from the Sun is Uranus. It is about 4 times bigger than Earth. It takes Uranus 84 Earth years to revolve around the Sun. But it rotates in just 17 Earth hours. It is blue-green in color with rings and has at least 21 moons.
Neptune is as big as Uranus. Because it is so far away, it takes 165 Earth years to revolve around the Sun. Neptune rotates in 19 Earth hours. It has at least 13 moons.
Uranus is the only planet that rotates on its side.
Pluto is so far away that it takes 248 Earth years to revolve around the Sun. Pluto takes 6 Earth days to rotate. It is the smallest planet in the solar system. It is even smaller than Earth's Moon. Pluto has 1 moon, but no rings.
Is it a planet?
On March 15, 2004, a tenth planetlike object was discovered far beyond Pluto. This new object is called Sedna. It may be made up of rock and ice. Sedna is often called a "planetoid."
What did you learn?
What else orbits the Sun other than the planets?
What is Sedna?
Why does it takes some planets only days to revolve around the Sun and other planets more than one hundred years?
In this book you have read about the planets. Write to explain what makes Earth different from all the others. Use details from the book as you write.
How are the inner and the outer planets alike? How are they different?
How does technology affect our lives?
People always want to know how things work. As people learn things, they get new ideas. People invent tools to help. A tool helps people do work more easily or in a new way. This means people use technology. Technology is using knowledge to design new tools and new ways to do things. Tools can be simple or complicated.
Arches were an important invention in ancient Rome. An invention is something made for the first time. The Romans needed water for their cities. They learned that arches with a central stone could hold heavy things. They used these arches to make bridges. Bridges were used to move water to the cities.
The keystone, or central stone wedged at the top, keeps the stones of the arch in place.
Technology in Your Home: 
Your home is made up of many parts. These parts form systems. The systems must work together.
What happens when you flush the toilet? You use the plumbing system. This system is made of faucets, drains, sinks, and pipes. These parts all work together.
Some water in the plumbing system goes through a heater. The electrical system is linked to it. Electricity heats the water. Together, the plumbing and electrical systems make it possible for you to take a hot shower.
How is a house built? Technology is used from the beginning. Boards are placed in very special ways. Builders know where to place boards to make a house strong. Each part must be put in the right place to make a strong frame. This is why planning is important.
Particle boards are used in walls. The boards are made of wood chips. Such wood chips used to be burned. When burned, they caused pollution. New technology turns those chips into strong boards that are used in walls.
Wood chips are pressed and glued together to make particle boards.
Technology Yesterday, Today, and Tomorrow: 
Two hundred years ago, kitchens did not have electricity. There was no refrigerator. People had to burn wood in a stove to cook food. Cooking meals could take all day.
People began inventing new things. First, ice boxes were used to keep food cold. Then, electric refrigerators replaced ice boxes. Today, microwave ovens cook food in seconds. Electric dishwashers wash dishes for you.
Airtight seals for plastic bowls were invented in 1947.
The non-stick coating on this pan was invented in 1954.
In the past, people played records to listen to music. As a record spun, a metal needle moved along the grooves of the record. Then a machine turned the vibrations from the needle into music. Today's DVD players use light beams to read the information on computer-coded plastic discs. Then a computer changes the information from the discs into images on a screen.
Some people think that computers will run your entire home in the future. A refrigerator may be able to order food when it becomes empty. Technology may make this possible.
What are some new technologies?
Tools for Extending Our Senses: 
Sailors once used math and the stars to find their way. Now they can use a Global Positioning System (GPS). This system uses space satellites. The satellites send signals. A ship's GPS computer uses the signals like a map. Many cars today have a GPS.
Satellites can be used in many other ways. Forecasters use pictures taken by satellites to predict the weather.
A computer stores, processes, and sends electronic information very fast! Computer technology is all around you. Computer chips are found in digital watches, cameras, and even cars.
Optical fibers are making computers better. These fibers are strands of bendable glass that carry light. The fibers are replacing copper wires in computer and telephone systems. Optical fibers do not get hot, as wires do. They also take up less space than wires. They can even carry much more information.
Roads are important to us. We use them to get to school and to work. We use them to transport goods. We use them to visit friends and family.
The National Highway System is made up of over 160,000 miles of highways. These highways go between the states in our country. About 80 million trucks haul supplies on these highways. About 120 million cars move people from place to place.
Roads are not the only way of moving people and things. People and freight are moved using trains and planes too.
But rivers were the first transportation system in the United States. Rivers are still full of boats moving goods today. Technology will always keep things moving!
Technology uses are not always planned. The microwave oven is a good example. In 1946 Percy Spencer was working to improve radar. He was testing a light bulb. The bulb used microwave energy.
One day, Spencer stood by the tube. A candy bar in his pocket melted. Spencer then placed popcorn kernels near the microwave energy. They popped. Spencer discovered that microwaves could cook foods fast! Soon, the microwave oven was invented.
This is Percy Spencer's design of how a microwave oven would work.
Do you watch TV? Glass tubes were used to show the picture in early television sets and computers. But these tubes were big and heavy. With new technology, screens are light in weight. The LCD screen was invented in 1970 by James Fergason. LCD stands for liquid crystal display. Liquid crystals control the flow of light. This makes an image on the screen. These screens do not need heavy glass tubes. They are also flat in shape. So they take up less space.
Flat LCD screens take up less space than older glass screens.
How does technology help us get energy?
Put in a DVD. Heat up a snack in the microwave. Just be sure everything is plugged in! None of this would be possible without electricity.
Before electricity, people used energy from wind and water. Water-powered mills were built near rivers. The force of flowing water turned a wheel. At a sawmill, the wheel turned rods, gears, and belts. This powered saws that cut wood.
Windmills were also used to do work. Windmills use wind for power. Turning blades move gears in a box. Energy in the gears moves a rod up and down. This can be used to pump water from under the ground.
There are good and bad things about using windmills and water mills. Both wind and water are renewable sources of energy. They do not cause pollution. But they don't make enough power for all our needs.
Windmills use wind to pump water.
Producing Electricity: 
Waterwheel technology is still used in hydroelectric power dams. These dams are built on rivers. Water in lakes behind the dams stores potential energy. To free this energy, gates let water into a power station. The flowing water spins the blades of a waterwheel in a turbine. The kinetic energy of water is changed into electricity in a generator. People use the electricity for power.
This generator can change the kinetic energy of flowing water into electricity.
Connected to each generator is a turbine. The energy of moving water spins the blades in the turbine.
Hydroelectric power does not make much pollution. But the lakes behind dams can cause flooding.
There are other ways to make electricity. One way is by burning coal, oil, or natural gas. The heat created is used to boil water. The boiling water makes steam. Pressure from the steam turns wheels in electricity generators.
This technology makes plenty of electricity. But it also creates the problem of air pollution.
Hoover Dam is one of the largest dams in the world.
Our need for energy keeps growing. How will we keep meeting this need?
Solar energy may be one answer. This energy comes from sunlight. Special panels collect sunlight. Each panel has lots of small solar cells. They change energy from the Sun into electricity. Solar energy is common in deserts. The Sun shines there much of the time.
Thanks to new technology, solar energy costs less. People can buy panels to put on their roofs. But these panels make hot water, not electricity.
Here's how it works. First, water runs through small tubes. Next, the Sun's rays are changed into heat. This happens when the panels absorb the rays. Then the heat warms the water in the tubes. Finally, the hot water flows into a tank. It is stored until it is used.
Wind energy is helping too. Windmills are put in places that get strong winds. Huge blades change the kinetic energy of wind into electrical energy.
Computers are used to tell when wind conditions have changed. Motors then adjust the direction and angle of the blades. This way, electricity is made whenever strong winds blow.
Windmill blade wheels can be wider than a football field is long!
Technology makes new ways of creating electricity possible. It also helps the systems in your home to work together. Technology helps us every day. It has changed our lives in many ways. Who knows how technology will change our lives in the future.
What did you learn?
What invention helped the Romans get water to their cities?
How has modern technology changed kitchens?
Why are optical fibers better than wires?
In this book you have read about water mills and windmills. Write to explain how each works. Use examples from the book.
Explain how solar panels heat water that goes into a hot water tank.
Animal Groups: 
There are lots of different animals in the world. When animals are grouped together, we can see the things they have in common. You can learn many different things about animals when you group them. This is because animals can be grouped in so many different ways.
What All Animals Need: 
All animals need food, water, oxygen, and shelter.
Animals need food and water for their systems to work. Oxygen is a gas that animals breathe. They need oxygen to stay alive. Animals that live on land use their lungs to breathe. Animals that live in the water use their gills. Shelter provides animals with a safe spot to rest or to hide from other animals.
Ways of Grouping Animals: 
The way you group animals should depend on what you want to learn about them. If you want to learn about animals' environments, group them by where they live. If you want to learn if animals are herbivores or carnivores, then group them by what they eat. Animals can also be grouped by the traits they share. A trait is a feature that is passed on to a living thing from its parents. Webbed feet or fins are traits that are passed from parents to their young.
A vertebrate is an animal with a backbone. Reptiles, amphibians, fish, birds, and mammals are all vertebrates.
Reptiles have lungs. Their skin can be dry and scaly.
Amphibians spend time in the water and on land. They have gills when they are young. When they get older, they usually grow lungs.
Fish have gills, never lungs. They live only in the water.
Mammals have hair during some part of their lives. All mammals breathe through lungs.
Birds have lungs too. They also have wings, beaks, feathers, and light bones.
Most animals in the world do not have a backbone. Sea jellies, worms, mollusks, and arthropods are all animals without a backbone. Insects and spiders do not have backbones.
Animals without a backbone usually do not grow very big. Think about how small most insects and spiders are when compared to a mammal.
Some animals have a shell or outside skeleton instead of a backbone. A shell or outside skeleton can give the animal support.
Animals Grow and Change: 
As animals grow and change, they go through life cycles. Every animal's life cycle has a set order. Animals grow and change in a certain order.
Certain life cycles take a long time. Other life cycles are very short.
All animals come from eggs. Sometimes the egg grows inside the animal's mother.
The mother then gives birth to the animal.
Other times, the mother lays the egg. The animal then hatches from the egg. The first stage of an animal's life cycle is birth.
An animal grows bigger during its growth stage. Then it develops into an adult. Adults give birth to young animals through reproduction. An animal's life comes to an end with death.
A Butterfly's Life Cycle: 
A butterfly is an insect.
It goes through many changes during its lifetime.
First an adult butterfly lays a very small egg on a plant. A caterpillar hatches from that egg. It does not have wings.
Next the caterpillar eats and grows.
It sheds its skin many times. During this stage the caterpillar is called a larva.
Then a hard shell, or chrysalis, forms around the caterpillar. The caterpillar becomes a pupa. Inside the chrysalis, the caterpillar keeps changing.
Finally a butterfly comes out of the chrysalis. Now the butterfly is an adult. After it lays eggs, the butterfly completes its life cycle.
Snakes are a kind of reptile. Some snakes live on the land and in the water.
When a female snake is ready, she lays her eggs in a warm, damp, and dark place.
A young snake uses its egg tooth to cut through its eggshell. The egg tooth will fall off later.
Snakes can grow very fast. After a baby snake has grown enough, it sheds its old skin and grows a new skin.
Most snakes become adults by the time they are two to four years old. Once a female snake becomes an adult, she is ready to lay eggs on her own. The snake life cycle starts again.
Mammals go through smaller changes during their life cycles. They give birth to their young. Young mammals grow inside their mother's body. When mammals are born, they usually have fur or hair. Young mammals get milk from their mother's body. Some mammals grow up quickly.
Adaptations Help Animals: 
You have learned that animals need food, water, oxygen, and shelter to stay alive. Animals also have special features that help them survive in their environment. Every environment is different, so each animal has adapted to the environment where it lives.
An adaptation is a special trait that helps animals survive where they live. The camel's long thick eyelashes are an adaptation for the desert. They protect the camel's eyes and keep out blowing sand.
A male lion has a very thick mane around its neck for protection.
These body part adaptations are inherited. Things that are inherited get passed from adults to their young.
All animals need food to survive. Sometimes they develop adaptations that make catching or eating their food easier.
An animal may be adapted to run very quickly, like a cheetah. Cheetahs need to chase their food to catch it.
An animal may have very good eyesight and hearing. Owls use both of these senses to hunt at night.
Giraffes have very long necks so they can eat leaves that grow in tall trees.
Many animals have developed adaptations to protect themselves.
Skunks are small animals that release a strong-smelling spray when they are scared.
Other animals use camouflage to hide from their enemies.
Polar bears are adapted to use camouflage in their snowy environment. It is very difficult to see a polar bear because the color of its coat blends in well with snow.
Behaviors That Help Animals: 
Animals behave in many different ways.
A behavior is something that a living thing does. Animals are born knowing some behaviors, but animals must learn other behaviors.
A baby bird is born with wings, but that does not mean the bird can fly right away.
The bird must learn to fly.
Instincts: 
An instinct is a behavior that does not have to be learned. Animals have instincts. When the weather changes, some animals have an instinct to migrate, or move.
Snow geese migrate in large groups during the winter. They fly from areas that get very cold to areas that are warmer.
Other animals hibernate or rest for long periods of time. When animals hibernate, they go a long time without waking up, eating, or drinking. Black bears hibernate during the winter. They hibernate because the food they eat is harder to find in the winter.
Learning: 
Animals are able to learn different ways to survive in their environment too. Sometimes an animal will learn a behavior from its parents. Young wolves learn how to hunt by watching adult wolves. In the same way, young beavers learn how to build beaver dams and homes by watching their parents cut and move branches and logs.
Animals Then and Now: 
Sometimes looking at the past can help explain the present. By learning about animals from the past, you can also learn about the animals of today Today's animals are alive because they were able to adapt. Animals from the past provide clues about the changes to animals over time.
We learn about animals from long ago by looking at fossils. Fossils are signs of past life. Fossils can be whole skeletons or a single bone. Sometimes an impression of a skeleton or bone is found in a rock. By looking at fossils, fossil molds, and casts, scientists can tell how big an animal was. Scientists may also be able to tell whether an animal ate plants or meat, just by looking at fossils.
Ancient Insects
Sometimes scientists will find more than just fossil bones. Whole animals, such as small insects, get caught in tree sap. Over time, the sap turns into a hard yellow or brownish substance called amber. Because we can see through amber, scientists have been able to look at insects from long ago.
How Today's Animals Compare With Those of Long Ago:
Scientists like to study both plant and animal fossils. From fossils, scientists can often figure out what the weather was like. Using all of the clues that fossils give, scientists are often able to figure out how today's animals adapted to the Earth's changes.
Grouping animals helps you learn more about them. There are many ways to group animals.
By grouping animals, you can learn about how animals are the same and how they are different.
What did you learn?
What are the vertebrates that live in your area? What do they look like?
What are the different stages of an animal's life cycle?
What adaptation helps a cheetah get food?
Animals can be grouped in different ways. Using your own paper, describe some of the ways animals can be grouped. Use details from the book to support your answer.
Describe the life stages of a butterfly in order. Use the words first, next, then, and finally in your answer.
Places for Living Things: 
Living things get what they need from where they live. A living thing's environment is everything that is around it. Plants and animals are living parts of an environment. Some nonliving parts are sunshine, water, soil, and weather.
Sunshine warms the air, water, and soil.
It allows plants and animals to live in those places. Water and soil are important parts of the environment. Water falls as rain and snow. It goes into the soil. Some soils hold a lot of water. Other soils hold very little. Plants need different types of soil.
Climate is the weather a place has during the year. In some places, the climate is cold and dry. In other places, the climate is hot and wet. Many places have climates with changing seasons.
Plants and animals live where they have water, food, and shelter. An ecosystem contains all the plants, animals, and nonliving things in an environment. The different parts of an ecosystem work together.
Prairie dogs dig holes in the soil. This gives the soil more air. The air helps the grass grow. This makes more grass for animals to eat.
The living parts of an ecosystem also need each other. Burrowing owls and other animals often use the holes dug by prairie dogs.
Special Homes: 
Every plant and animal has a special place to live. This place is called its habitat. Living things get what they need in their habitat. Plants get light, air, water, and space to grow. Animals get food, water, and a space to live and grow.
If one part of a habitat is taken away, the habitat will change. If prairie dogs leave their habitat, the animals that use the prairie dog holes might have to move or find other places to live.
The cactus lives in a desert habitat.
The elephants are able to get water and rest at the lake. They take care of each other. The elephants make up a population.
Birds come to live at the lake. They make nests and find fish in the lake. Other animals find food at the lake too. The elephants, birds, and other animals each belong to their own populations. Together they make up a community of animals. The animals in the community need each other and the lake in order to live.
Ecosystems Change: 
Sometimes ecosystems change. First, one part of the ecosystem changes. Then the other parts change too.
Long ago, many wolves lived in Yellowstone National Park. The wolves ate elk and other animals. People wanted to get rid of the wolves. They killed many of them.
When the wolves were gone, there were not enough animals to eat the elk. Yellowstone's elk population grew out of control. There were too many elk and not enough food. Many of the elk died.
A grassland is a large, flat area of land that is covered with grass. There are grasslands all over the world. The grasslands of North America and Asia usually have cold, snowy winters and hot summers. African grasslands are much warmer.
In some grasslands the soil is too dry for trees to grow. Trees need more water than the grassland gets.
During the spring and summer, it rains in the grassland. The rain soaks into the ground. The grasses have long roots that go deep into the ground. These roots can get water in the drier seasons.
Some grasslands get more rain than other grasslands. Tall grasses can grow in these grasslands. Short grasses grow where there is less rainfall. Wildflowers grow in grasslands too.
Many animals live in a grassland ecosystem. Rabbits, deer, and prairie dogs eat the grasses. Foxes, snakes, and other animals eat the smaller animals. Birds such as owls and sparrows also live in grasslands.
American bison, or buffalo, live in the grasslands of North America.
A desert is a place that gets very little rain.
Most deserts get less than five inches of rain a year. During the day the desert can be very hot. At night it is much cooler.
The plants and animals in the desert need each other. All of the desert's living things have found ways to stay alive without needing much water.
One kind of desert plant is the cactus. Cactuses keep water in their stems. Their roots spread out to get water from the soil. They have special skin that keeps water in.
Desert animals hide when it is hot. Some sleep in the shade of plants. Others, such as some frogs and toads, dig tunnels under the ground. Desert animals such as snakes and coyotes often go out at night when it is cool to hunt for birds and other small animals.
When days are hot, the rattlesnake hunts at night.
The Arctic tundra is a very cold and dry ecosystem. It is located near the North Pole.
Winters on the tundra are long and cold. Some snow falls, and it is very windy. The days are short, and the nights are very long. For many weeks the Sun does not shine at all. The ground is frozen all the time.
Summers on the tundra are short and cool. The days are long and sunny. In some places, the Sun shines twenty-four hours a day. The snow melts, but the soil under the ground stays frozen.
Many plants, such as trees, can't grow in the tundra. In fact, the word tundra means "treeless land."
Other plants, such as grasses and wildflowers, can grow there. These plants are small and have short roots. Many tundra plants have tiny hairs on their stems or leaves. The hairs help protect the plants from the wind.
In the summer, ponds form on the tundra. Ducks, geese, and other birds make nests near the ponds. There are many insects to eat during the tundra summer. Most of the birds in the tundra fly to warmer places in the winter.
Lemmings are small animals that live in the tundra. They dig in the snow to find grass, moss, and twigs to eat. They have thick fur that helps keep them warm.
Most of the tundra's flowers and plants are small. This helps protect them from the strong winds.
Earth has many different kinds of forests.
Each forest has its own plants and animals.
Coniferous forests grow in places with warm summers and cold, snowy winters. Coniferous trees have leaves that look like needles. Both spruce and pine trees are conifers.
Coniferous trees grow close together.
This helps protect them from the cold and wind. It is hard for plants to grow under conifers. They don't get enough sunlight. Moss, however, grows beneath these trees.
Many animals, such as bears, live in coniferous forests. Bears have thick fur to help them stay warm. They sleep through the cold winters. Birds eat seeds from the trees in summer. Then they fly to warmer places in winter.
Deciduous forests grow where it rains in the summer and snows in the winter. In the fall, the leaves on deciduous trees change color.
They change from green to yellow, orange, or red. Then the trees drop their leaves. In the spring, they grow new leaves that stay green all summer. Both oak and maple trees are deciduous.
It is easier for plants to grow in deciduous forests. Flowers, ferns, and moss grow on the deciduous forest floor.
Many animals live in a deciduous forest. Insects, birds, and small animals make their homes in the trees. Many small animals eat the trees' leaves, nuts, and seeds. Owls and foxes live in deciduous forests. They find squirrels and other small animals to eat.
Tropical forests grow in places that are mostly warm and wet all year long. The trees that grow there are very tall. Some tropical forest trees are as tall as a ten-story building! The leaves on top of the trees keep much of the sunlight out.
Many plants can't grow under the trees because they don't get enough sunlight.
Some plants can grow on the branches and trunks of the trees. These plants are called air plants. They get water and food from the air. Vines also grow on the trees.
Many animals live in the tropical forest.
Most live in the trees. Frogs and spiders live under the leaves. Ants and beetles live under the bark. Snakes wind around the trunks. Monkeys swing from tree to tree, and colorful birds sit on the branches.
Many, many insects live in tropical forests. How many? So many that scientists haven't even named them all!
Many tropical forest insects are hard to see. They look like sticks or leaves.
Orchids are air plants. Their roots dangle in the air to get food and water.
Some ecosystems have fresh water. Other ecosystems have salt water. In some places fresh water and salt water come together.
Lakes, ponds, rivers, and streams are all freshwater ecosystems. Lakes and ponds have land all around them. In rivers and streams, the water moves from one place to another.
The water in some lakes and rivers comes from under the ground. The water in others comes from rain or melting snow.
A wetland is land that is covered by water most of the time. Trees, grasses, and plants grow in a wetland. Many animals live there too. Some wetland birds have long legs that help them walk in the water. They have beaks for catching fish to eat. Wetland frogs and toads can live in the water and on the land.
The largest freshwater wetland is in Brazil. Many large rivers run through Brazil. When it rains, these rivers can overflow, flooding the surrounding land. The flooded land becomes a wetland habitat for many plants and animals.
Many birds stay in the wetlands of Brazil for a short time while they are traveling to other places. Many fish live there too. The wetlands of Brazil are also home to capybaras. They have webbed feet, like a duck. Their webbed feet help them swim.
Capybaras' eyes and ears are on top of their heads. This helps them to see and hear when swimming.
Saltwater Ecosystems: 
Earth's oceans contain almost all of its salt water. They cover most of the planet. Near the land, the ocean is not very deep. Clams, crabs, and some kinds of fish live there.
Far from land, the ocean water is deep. Large fish, sharks, and whales can live in deep water.
The deepest parts of the oceans are dark and cold. Very few plants can grow there because there is little sunlight.
Rivers flow into oceans. The fresh water from rivers mixes with salt water from the ocean. When this happens, salt marshes are formed.
A salt marsh is a type of wetland. Most of the salt marsh is covered with water. Many grasses grow in the salt marsh. These grasses can live in water and soil that is salty.
Some of the animals in the salt marsh are so small that you can't see them. Many sea animals start their life in salt marshes before moving out to the ocean.
Flamingos eat the tiny insects and plants found in salt marshes.
The World Around You: 
We have now talked about many ecosystems.
Yet there are still thousands more, found all over Earth. Ecosystems are everywhere. But they are difficult to define and measure because they are always changing. Climate changes. Hurricanes, and volcanic eruptions change ecosystems. Human activities and the interactions between plants and animals also change ecosystems.
Ecosystems' constant changes can be difficult and confusing to track. Many people try to get rid of that confusion by thinking of Earth as one big ecosystem! However you like to think about it, one thing is for certain: ecosystems need to be protected, so every living plant and animal can have a home.
What did you learn?
What happens when one part of an ecosystem changes?
Why can't trees grow in some grasslands?
Lemmings are able to live on the tundra. Why?
You have read about the importance of prairie dogs in their habitat. Write to explain the things that prairie dogs do to help keep other living things alive.
A tropical forest is one kind of ecosystem. List some details from the book about this forest.
Earth is a very special place. One of the things that makes it special is the way plants and animals live together, or interact. Sometimes they live together in a way that helps one another. Other times, they live together in a way that hurts one another. Plants and animals can also live together in ways that neither help nor hurt one another. Living things interact in many different ways. However, all living things need other living things in order to live.
How Living Things Interact: 
Some animals live together in groups and help each other out. When an ant finds some food, it tells other ants where the food is. Together, the ants carry the food back to their home.
Canada geese with goslings often gather with other mother geese and their goslings. One or two of the mothers will watch over the goslings, while the rest of the mother geese go hunting for food.
Animals who live in herds may form a tight circle for protection against bad weather or an enemy. Horses caught in a snowstorm will put their heads together in a circle for warmth. Often, older horses will push the younger horses into the center of the circle for added protection.
Sometimes when two animals interact, only one animal will be helped. This happens when a barnacle attaches to a whale. The adult barnacle does not swim on its own. Instead it eats the bits of food that flow past as the whale swims. The whale is neither hurt nor helped by having the barnacle on its body.
Sometimes plants and animals work together to help each other. Fruit bats help pollinate certain fruit trees in tropical rain forests. The trees get pollinated and the bats get a meal.
Living Things Get Energy: 
For plants to be able to grow, bloom, or make seeds, they must have energy. In order for animals to be able to build homes and search for food, they must have energy.
Green plants are the only living things that can make their own food. They do this by taking energy from the Sun.
Green plants are able to make their own food. This makes them producers. All other living things get energy from the foods they eat. This makes them consumers. Consumers get their energy by eating green plants, or by eating animals that have eaten plants.
Carnivores, Herbivores, and Omnivores: 
It can take a long time for the energy in a plant to get to an animal. This is because not all animals eat plants. Animals that eat only meat are called carnivores. You already know about many kinds of carnivores. Tigers, eagles, and mountain lions are carnivores.
Animals that eat only plants are called herbivores. Goats, horses, and rabbits are herbivores. Some animals eat both plants and other animals. These animals are known as omnivores. Chimpanzees are omnivores. They eat insects, fruits, seeds, and many other things.
You might have questions about how carnivores get their energy from green plants. The answers are found by looking at a food chain. Energy moves from producers to consumers in a food chain.
Think of a clover plant growing in a field.
The clover plant is green. It makes its own food energy from sunlight. The clover is a producer.
Rabbits are herbivores. They eat the clover.
By eating the clover rabbits take in energy from the plant. Rabbits are consumers.
Marsh hawks are carnivores. They eat rabbits. If a marsh hawk catches and eats a rabbit, it will get energy from the rabbit. Now think back to where the rabbit got its energy. Do you remember? It was in the clover that the rabbit ate. The marsh hawk gets energy from both the rabbit and the clover.
Food Chains: 
All living things belong to a food chain. Food chains start with a producer, such as clover. At the end of each food chain is a consumer, such as the marsh hawk.
Most food chains have predators and prey.
A predator is an animal that hunts for its food. Prey is the animal that is hunted. The marsh hawk is a predator, and the rabbit is its prey.
There can be more than one food chain in one place. In a field where clover grows, grass might also grow. Mice eat the grass. Owls eat the mice. In this food chain, grass is the producer. The mice and the owls are consumers. Owls are predators. They hunt the mice, which are the prey.
Another food chain could start when a plant's leaves are eaten by a deer. That deer could become prey for a bobcat.
Food Webs: 
One food chain cannot show all the plants and animals that pass on energy, even in a small place. Plants and animals might be eaten by more than one thing. Food webs show what happens when food chains cross.
Look at the food web on the right. You read that marsh hawks eat rabbits. They can also eat mice. Owls can eat rabbits. Bobcats can eat deer, rabbits, mice, and even hawks! Food webs show interactions between many living things in an environment.
How Food Webs End and Change: 
It may seem like the food web that we just described ends with the bobcat. However, people sometimes hunt top predators such as bobcats. Other times, accidents, disease, or natural disasters may also kill animals such as bobcats.
If that happens, scavengers such as bugs, crows, and coyotes will eat the bobcat. A scavenger is an animal that eats garbage or dead animals.
What would happen if one part of a food chain disappeared? For example, suppose a lot of mice were killed or died. The barn owls and marsh hawks might not have enough food. That might cause the hawks and owls to go hungry.
If they became hungry enough, they might be forced to move to a different place.
How Living Things Compete: 
If the barn owls and the marsh hawks both wanted to find mice, they would be in competition for the mice. In this case, two different kinds of predators are in competition for food. Usually, the stronger and faster predator will succeed.
Sometimes the competition between living things is not for food but for space. New homes may be built where animals used to live. Because of this, people may find deer in their backyards eating garden plants and bushes.
Many years ago, a plant called kudzu was brought to the United States. After a few years the kudzu started growing all over trees and bushes. It began to cover and choke out other plants. The kudzu was too successful at competing with other plants for space to grow.
Environments Change: 
Environments can be changed by more than just plants competing for space. Animals or natural events can also change an environment.
The gypsy moth is an animal that has changed the environment in many parts of the United States. This insect's larvae eat the leaves of many kinds of trees. When gypsy moth caterpillars eat too many leaves off too many trees, birds lose their homes. Gypsy moth larvae can eat enough leaves to cause some trees to die.
Tornadoes, hurricanes, floods, droughts, volcanic eruptions, and fires are all natural events that can change environments. These natural events sound bad, but they can also bring some good changes to the environments they affect.
Tornadoes and hurricanes blow down many trees. Many living things grow on these trees. If a tree gets blown over and dies, it will soon be covered with decomposers. A decomposer is a living thing that breaks down waste and things that have died. The decomposers help the dead tree to decay, or rot. After the tree decays, it becomes part of the soil again. Other trees need the fertile soil from the dead tree so they can grow.
A Healthy Environment for People: 
People are at the top of many food chains and food webs. We are consumers of both plants and animals. Most people in the United States do not grow or catch their own food. They go to a grocery store to buy it. It is important for people to eat lots of fruits, vegetables, dairy products, nuts, whole grains, and fish in order to get the vitamins and minerals needed for good health.
In addition to good food, people need clean air and water, shelter, and a clean environment.
In order to stay healthy, people also need to exercise. You can get exercise by working, playing sports, or playing outside.
People must also keep themselves clean so they don't get sick. It is important to wash your hands before eating so diseases are not spread.
A disease is a sickness. Germs can cause disease. A germ is a very small living thing or particle that can make you sick.
People should also take good care of the world around them. They can help keep the air and water clean to protect all living things.
What did you learn?
How do animals get energy to hunt for food?
What scientific term describes what happens when grass grows, gets eaten by a mouse, and then that mouse gets eaten by an owl?
What kind of animal has caused harm to many trees in the United States by eating too many of their leaves?
In this book, you have read about producers and consumers. Describe how producers and consumers interact. Use examples from the book.
Suppose you have seen a lot of mice in your backyard. You have also seen hawks hunting them. Suppose that one day you saw far fewer mice and no hawks. What might you conclude?
The Water of Life: 
All living things need water to survive. Plants, animals, fish, insects, birds, and human beings all depend on water to stay alive.
Think about food, shelter, clothing, and water. Which is the most important? If you answered water, you are right. We need the others also, but without water we could live for only a few days.
Many of Earth's living things spend their entire lives in the water.
You know about animals such as fish and clams and other sea creatures.
But there are also lots of living things in the water that are difficult to see. For instance, a living thing called a paramecium lives in ponds and lakes. A paramecium is much too small to see without a microscope.
All Living Things Need Water: 
About two-thirds of your body is made up of water. It helps your body's parts work correctly We must drink plenty of water because our bodies lose a lot of it through sweat. We sweat water to keep our bodies at the right temperature.
Tears in your eyes wash out dust. Saliva in your mouth helps to digest food. Blood, which is mostly water, carries oxygen and nutrients through your body. The water in your blood also carries away waste from your organs.
Running makes us sweat.
This land is watered so that crops can grow.
How We Use Water: 
Farmers who grow lots of food use huge amounts of water to raise their crops. More than half of the world's fresh water is used for growing food. Farmers bring water to their fields from rivers, lakes, reservoirs, and wells. That allows them to grow crops in places that get very little rain.
People have learned to use water in many ways. Huge ships can move easily in water. Because of that, people can move goods from place to place all over the world.
When people learned to use the power of water, many things changed. Dams were built to block rivers. They help control flooding. Dams also help make electricity. People all over the world use electricity from dams to heat and light up their homes.
Salt Water versus Fresh Water: 
Almost three-fourths of Earth is covered by I the salt water of the oceans. People use salt water for transportation and fishing. Salt water cannot be used for drinking, bathing, or cooking. It cannot be given to animals. It also does great harm to land-based plants, so it cannot be used to water crops.
Only a small part of Earth's water is fresh water. Fresh water is found in ice, snow, rivers, lakes, streams, and in the ground. About two-thirds of that fresh water is frozen in glaciers and ice caps at the North and South Poles. That leaves little fresh water for people, plants, and animals to live on!
The fresh water in streams and rivers is always flowing. Gravity makes a lot of fresh water sink beneath Earth's surface. Fresh water that is below the surface is called groundwater. By digging wells, people bring groundwater up to the surface.
When a river, lake, or stream overflows or floods, wetlands are created. Wetlands are marshy, soggy areas that soak up the extra water from the land. They help control flooding. Many birds and animals are adapted to live in wetlands.
When you put water into a tray and set it in the freezer, its temperature drops. When it reaches 32 degrees Fahrenheit, the water freezes and becomes a solid. Snow and hail are also solid forms of water.
When water is heated, it evaporates, becoming water vapor. Steam is the same as water vapor. The process is called evaporation. Evaporation causes water to change from liquid to gas without boiling.
The surface water on lakes and oceans is constantly evaporating into the air due to heating from the Sun.
Water vapor is invisible. But we can feel it on humid days. On humid days we feel "sticky" because our sweat doesn't evaporate as well.
At night when the Sun goes down, the air cools. Water vapor may turn back into a liquid at that time. This process is called condensation. Dew is a type of condensation. It helps plants grow. Clouds and fog are also forms of condensation.
Earth's water is used over and over again. It travels between the air, the land, and the oceans in an endless circle called the water cycle.
When raindrops hit the ground, different things may happen. Surfaces such as sidewalks can't absorb water. Raindrops that have fallen on sidewalks often evaporate.
Raindrops that have fallen on earth often seep downward through rocks and soil. They may reach groundwater. By doing so, they help refill the underground water supply.
If raindrops don't evaporate or soak into the soil, they may run downhill into a stream, river, or lake.
Then the drops may be carried to the ocean.
Water vapor rises from the ocean.
No matter how much water evaporates into the air, it always falls back to Earth in some form of precipitation. Precipitation may fall as rain, sleet, snow, or hail. If the air is cold enough, raindrops freeze into hail. Snow is made of tiny ice crystals in clouds. Whichever way water returns to Earth, the water cycle starts again.
Water contains substances we cannot see.
Many of them are good for us. But water can also contain things that are dangerous for us to drink. Pollution, germs, and chemicals in water can make us sick. Because of that we must add and remove things from our water before we drink it.
Cities and towns treat fresh water before it comes into our homes and businesses. Water is piped in from wells, rivers, streams, lakes, and reservoirs.
A city needs a lot of clean water.
On its way to the city, the water is cleaned by filters. The first filter catches large objects.
Another filter made of sand and gravel takes out any impurities that are left. Then air is bubbled through the water to make it taste fresh. Certain safe chemicals are added to get rid of germs and make the water safe to drink.
What did you learn?
Why is water so important to us?
How much of our bodies are made up of water?
What is the difference between salt water and fresh water?
In this book you read about water. Write to explain how the water cycle works.
What is the cause of dew? What positive effects does it have?
Some people love rainy days. Other people prefer hot, sunny days. When we talk about rain, sun, and temperature, we are talking about weather. The weather affects us every day.
If you don't like the weather one day, just wait. Weather always changes. Different parts of each country usually have different kinds of weather. Everywhere you go in the world, the weather is different.
The Atmosphere: 
Water vapor in the atmosphere helps cause weather. The atmosphere is made of air that surrounds the Earth.
This air is made of gases.
To understand the weather, we study the air in the atmosphere. Information about the air's moisture, speed, and temperature can tell us about the weather.
The atmosphere presses down with a force called air pressure. When the air pressure changes, the weather often changes too. Low air pressure often means the weather will be cloudy or rainy. High air pressure often makes dry, clear weather.
Studying the Weather: 
Scientists study the weather by using special instruments. Barometers measure air pressure. Anemometers measure wind speed. Hygrometers measure water vapor in the air. These instruments help predict weather changes.
Warm, wet air has humidity. This can often make the weather rainy. Scientists use a hygrometer to measure humidity. They can also use a rain gauge while it's raining to figure out the amount of rainfall.
Hygrometers, barometers, anemometers, and rain gauges are all important instruments.
They provide information that is used to predict and record the weather.
Satellites tell what is happening with the weather. Satellites orbiting in space take pictures of the air as it moves over the Earth. Those pictures are sent back to Earth. The pictures are used to make weather maps. Weather maps show what kind of air is moving over the oceans and land.
Satellite pictures also help scientists track the pollution. Pollution can harm the Earth and change our weather.
Factories, cars, and airplanes cause pollution. They produce harmful gases. The gases get trapped in Earth's atmosphere.
These gases can get heated by the Sun. This changes the gases into smog and ozone. These are forms of air pollution.
Smoke from factory chimneys harms the atmosphere.
Factories, cars, and trucks create smog.
The smog pollutes the air over towns and cities. Too much smog makes it hard for people to breathe outdoors. When smog levels become harmful, weather reporters might issue a smog alert.
You can help to reduce air pollution by cutting down on car trips. You could also get rides in the cars of your friends. Using public transportation also reduces air pollution.
Cars produce gases that pollute our towns and cities.
Weather patterns are caused by many things. The Sun, oceans, and mountains all affect weather patterns. Some places get the same weather patterns again and again. One very typical weather pattern involves snowfall in New York State.
Let's take a look at how it works.
During the winter, New York State can get very cold. The air can't carry much moisture when it is cold. So why does it snow so much in New York State? New York is bordered by two of the Great Lakes, Lake Ontario and Lake Erie. The other Great Lakes are Lakes Huron, Michigan, and Superior. Lots of water evaporates from the Great Lakes, even in winter. Air moving in from the west absorbs the evaporated water. The air absorbs so much water that it can't hold it all.
By the time the air is ready to release the water, it has moved east, over New York State. So the air releases the water, which falls as snow during the winter. That's why it snows so much in the areas of New York State that are closest to the Great Lakes.
Hurricanes, tornadoes, thunderstorms, and blizzards are dangerous storms.
A hurricane is a big storm. It forms over the warmest parts of oceans. Heat from the warm water helps cause this storm. The center of a hurricane is called the eye. Strong winds swirl around the hurricane's eye.
Hurricanes can cause a lot of damage. The heavy rain often causes flooding. Hurricane winds can blow up to 155 miles per hour. These winds can blow over buildings, power lines, and trees. If you know a hurricane is coming to your area,
Hurricanes are large storms that form over the ocean.
A tornado is also a dangerous storm. It is different from a hurricane.
A tornado forms quickly and moves fast over a small area of land. Tornado winds can reach 250 miles per hour.
Tornado winds are much stronger than hurricane winds, but they don't affect as large an area.
Tornadoes are sometimes called twisters because they look like spinning towers of air. People say a tornado sounds like an airplane taking off or a train roaring down its track.
Thunderstorms and Blizzards: 
Storms that cause rain, thunder, and lightning are called thunderstorms. Thunderstorms, which usually last for short periods of time, can also cause high winds and hail.
Hail is water that freezes inside large storm clouds. The hailstones become heavy and fall to the ground as chunks of ice. Hail can happen even if it is warm.
A blizzard is a dangerous winter storm.
During a blizzard, temperatures drop and heavy snow falls. Strong winds blow the snow into drifts. Because of the wind and the snow, it is hard to see well.
Staying Safe During Storms: 
Storms can be dangerous. People need to know how to stay safe during them.
How do people know if a dangerous storm is coming? The National Weather Service staff monitors the weather. They send announcements to radio and TV stations. If there is a storm watch, it means a storm could happen in your area. If there is a storm warning, it means a storm is on its way. When people know that a storm is coming, they can get prepared.
The Weather and You: 
The seasons affect weather patterns.
The weather in some seasons helps living things to grow. The weather in other seasons can hurt living things. There are many different kinds of weather, each with its own causes and effects.
At first you might have thought that there was little you could do about the weather.
Now you know differently! By watching for National Weather Service reports, you can prepare for dangerous weather. By cutting down on car trips, you can help prevent air pollution. You can make a difference to the weather!
What did you learn?
What are two qualities of air that help people describe the weather?
What does a barometer measure?
How do satellites help us predict the weather?
You have now read about why it snows so much in New York State. Using words from the book, write to explain why New York State gets so much snow.
Make Inferences If there is a lot of traffic on a warm day in a large city, what kind of warning do you think it would be likely for a weather reporter to give?
Rocks Are Everywhere:
Rocks are solid objects that come in all different shapes and sizes. Have you ever wondered what our planet's rocks are made of? Rocks are made mostly of minerals. A mineral is a natural substance that is made of nonliving matter.
Rocks have different colors and textures depending on the minerals in them. A rock can be made of just one mineral or of many different minerals.
A rock's texture is the size of the bits of minerals, or grains, within it. A rock's color depends on the kind of minerals and other substances that are in the rock.
Scientists group rocks by their color, texture, and minerals. Rocks are also grouped by how they formed.
Igneous rock comes from a mixture of melted minerals and gases deep inside the ground. This blazing hot mixture cools and hardens as it moves toward the surface. If the solid rock cools quickly, its mineral grains can be large. But if the solid rock cools slowly, its mineral grains can be too small to see.
One kind of igneous rock is obsidian. Obsidian is dark, smooth, glassy, and very hard.
It forms when melted rock cools very quickly.
It can be used to make tools. Some obsidian stones have white designs on the surface where crystals formed. The designs look similar to snowflakes. Those rocks are called snowflake obsidian.
When water travels over the land, it picks up small bits of broken rock. When these bits of rock settle on the bottom of lakes, rivers, and oceans, they are called sediment. Over thousands of years, pressure can bind bits of sediment together.
This turns the sediment into sedimentary rock.
The remains of dead plants and animals can be buried under layers of sedimentary rock. After many years, these remains can turn into stone. Then the remains are called fossils.
The cliffs of the Grand Canyon, in Arizona, show layers of sedimentary rock.
The third rock group is called metamorphic rock. Metamorphic rock is igneous or sedimentary rock that has changed over a long time into a new kind of rock. Limestone is a sedimentary rock. Limestone becomes marble when it is heated and pressed for many years. Marble is a metamorphic rock often used in building.
Marble, a metamorphic rock, is often used to make floors.
When rocks melt, they mix, cool, and harden to form new igneous rock. When rocks are worn down, the remains form new sedimentary rocks. Under the right conditions, both igneous and sedimentary rocks can become metamorphic rock.
Rock particles are carried by rivers into the sea, where they form sedimentary rock.
Under pressure, igneous and sedimentary rock can form metamorphic rock.
Lava cools to form igneous rock on the slopes of volcanoes.
CD More About Minerals: 
Minerals are the most common solid material on Earth. Almost everything we use contains minerals.
Scientists can tell minerals apart by looking at things such as color, streak, hardness, and luster. Color is the easiest to notice. Some minerals come in different colors. Spinel, for example, is a mineral that can be red, lavender, blue, green, brown, or black. The most common variety of spinel is a clear red.
Streak is the color of the mineral in its powder form. You can find a mineral's streak by rubbing the mineral across a hard surface. The color of a mineral's streak is always the same. This is true even if the mineral itself comes in different colors.
Pyrite is a mineral. It is called "fool's gold" because it is often confused with gold. Pyrite's streak is black. Real gold has a yellow streak.
Hardness is how easily a mineral can be scratched. Hardness is measured on a scale of one to ten. One is the softest and ten is the hardest. The hardest mineral is diamond. It cannot be scratched by anything but another diamond.
Luster describes how a mineral reflects light.
Minerals in Our Lives: 
Anything made of glass has quartz in it.
You will find quartz in drinking glasses, TVs, radios, and clocks. Quartz is one of the most common minerals on Earth.
Electrical wires are made of copper.
To stay healthy, your body needs minerals every day! When you sprinkle salt on food, you are using the mineral halite. The iron in meat helps your red blood cells. Chromium is a mineral that may help prevent a disease called diabetes.
Calcium and magnesium are important minerals for your body. Calcium builds bones and teeth. Magnesium helps muscles tighten and relax.
Soil is the thin layer of loose material that covers most of the land on Earth. Plants, animals, and people all depend on soil.
Soil is made up of water, air, bits of rock, and nutrients. Nutrients are materials that plants need to help them grow. Some nutrients are the remains of living plants and animals that have broken down through a process called decay. Other nutrients come from the minerals in the soil.
Rabbits depend on soil for food and shelter.
Soil forms in layers. The top layer is called topsoil. It contains many nutrients. Below the topsoil is subsoil, where tree roots find their water.
The deepest layer is bedrock.
As bedrock gets broken down, it becomes soil.
Humus is found in soil.
It is made of decaying plants and animals.
Clay is made of small particles. Clay soil is thick, dense, and traps water.
Sand particles are large and have a lot of space between them. Water passes through sand. Silt has medium-sized particles. It lets the right amount of water in and out.
Loam is a kind of soil made of sand, silt, and clay. Crops usually grow best in loam because it has the right amount of sand, silt, and clay.
Rocks, minerals, and soil are everywhere. Without rocks, minerals, and soil, we wouldn't be able to live. So be sure to treat the earth beneath you well!
What did you learn?
Which kind of rock forms in layers?
What are three ways that minerals are described?
What are some ways minerals help you to stay healthy?
On page six, you read about metamorphic rock. Write to explain how metamorphic rock forms from limestone, based on what you have read.
How does soil with a lot of clay compare to soil with a lot of sand?
Earth's Layers
Our planet is made up of several layers of rock. Scientists learn about Earth by studying these different layers. Scientists study the layers near Earth's surface. They also study the layers deep under the ground.
The crust is the hard, rocky layer that forms Earth's surface. Below the crust is the mantle.
The mantle is the thickest layer of Earth. It is more than two thousand miles thick. It makes up more than most of Earth's total volume.
Geologists study Earth's crust.
The innermost layer of Earth is the core. It is made mostly of iron and nickel. Iron and nickel are metals. The core has two layers. Those layers are the outer core and the inner core. The outer core is a very hot liquid. At Earth's center is the inner core. It is solid and hard.
Earth is coolest at the crust. It is hottest at the core. Earth's core is about one hundred times hotter than the hottest desert!
Shapes on Earth's Surface: 
A landform is a solid feature formed on Earth's crust. Hills, mountains, valleys, and plains are landforms. Waterfalls, cliffs, islands, and caves are landforms too. Even volcanoes are landforms.
Landforms are of different shapes and sizes. But all landforms are alike in one important way.
They are all shaped by natural forces. Those forces include heat, wind, water, and ice.
Many landforms are shaped by moving water. Rivers carve out valleys as they flow. Sand and small rocks carried in rivers wear away the land. The material that is worn off gets carried away. Then it gets left in new places.
Volcanoes and Earthquakes: 
Volcanoes can cause rapid changes to Earth's landscape. They contain magma. Magma is hot, molten rock. It sits in pockets called magma chambers. Gases in the magma create pressure. The pressure forces the magma through a central vent. The central vent leads to the top of the volcano.
This is how a volcano erupts.
When the magma reaches the volcano's top, the volcano erupts. Sometimes magma erupts through side vents. But it usually erupts through the volcano's top.
Volcanoes send steam, rocks, and ash into the air when they erupt. Lava is magma that reaches the surface. It flows down the slopes and burns everything in its path. Lava is eight times hotter than boiling water! When lava cools, it becomes hard, igneous rock. That rock is a new part of Earth's crust.
California's San Andreas Fault is more than eight hundred miles long.
An earthquake is a natural force that shakes the ground. Earthquakes happen when pieces of Earth's crust rub together along faults, or cracks.
Earthquakes produce waves of vibrations. These waves move up and down and back and forth.
Powerful earthquakes can cause a lot of damage. Earthquakes that are closer to the surface cause more damage. The longer an earthquake lasts, the more damage it can cause. The nearer an earthquake is to a city, the more buildings will be damaged.
Earthquakes cause landslides, which also cause damage. Landslides are rocks and soil that slide down the side of a hill. They can destroy buildings and roads. Landslides also happen in the ocean. There they can create huge, dangerous waves.
You may not see weathering happen. But weathering goes on all the time. Weathering is a process that breaks down rocks on Earth's surface into smaller and smaller pieces. Plants, animals, insects, and other living things can cause weathering. Water, wind, and ice can cause weathering too. Sometimes weathering changes only take a few years. Other times they take centuries.
Plants are just one cause of weathering. Plants cause weathering by forcing their roots into cracks in rocks. As the roots grow, they split the rocks.
Water causes weathering too. Sometimes water picks up special chemicals from soil. The chemicals eat away at rocks the water touches. This is called chemical weathering.
Ice also weathers rocks. Water can get into cracks. When water freezes into ice, it expands. This splits rocks apart.
Ice can weather rocks in another way. Glaciers are huge masses of ice and snow. They scrape the ground beneath them as they move. This scraping causes many changes.
After rock is broken apart by weathering, the pieces often get carried away. This is called erosion. Wind, water, glaciers, and gravity all cause erosion.
Water is always causing erosion. Rivers carry away bits of rock and leave them in new places. This forms new islands. Rainwater and ocean waves also cause erosion.
Deserts lack water. Because of this, most desert erosion is caused by wind. Deserts have few plants to block the wind. They also lack plant roots to hold down soil. This means strong winds can cause lots of erosion.
Animals are another cause of erosion.
Worms, squirrels, and ants all dig holes in the ground. These holes let water and air into the soil. This causes further erosion.
Gravity causes erosion too. Broken rock and other materials often fall down hills as mudflows or rockslides.
Earth is always changing. Most of the time the changes are small and take a long time. Other times the changes are big and happen very fast. Look at the land around you. It may look the same from day to day. But that land is changing all the time!
What did you learn?
What are the three main layers of Earth?
How are landforms alike and different?
What's the difference between magma and lava?
Weathering and erosion work together to change Earth's surface. Write to explain how this works.
Describe how a volcano erupts, placing each step in order. Use the words magma and lava in your description.
What Resources Are: 
Resources are materials that help meet the needs of living things. Natural resources are important materials from Earth that living things need.
Trees are one example of a natural resource. Trees give people the material needed to make many things. Wood is used to make lumber for building homes. Wood is also used to make pencils and even paper.
Some other natural resources are water, soil, air, and sunlight. All these resources come straight from nature. These natural resources are used every day. You are always breathing air. You always need to drink water. Plants and trees need sunlight, soil, water, and air to grow.
What natural resources is this farm using to grow crops?
Some natural resources can be easily replaced. These are called renewable resources. We often plant new trees to replace the ones we cut down. If we eat all the crops that farmers grow one year, more can be planted the next year.
Resources We Cannot Replace: 
There are some natural resources that we cannot make again. Earth can run out of many resources.
Once we use them up, they are gone. These resources are called nonrenewable resources.
Many nonrenewable resources are used for very important tasks. A lot of them, such as natural gas, oil, and coal, are used as fuel. Once these resources are used up, we cannot make any more of them.
Some resources are always available on Earth. Sunlight, air, and water cannot be used up.
This new car runs on electricity and gasoline. It creates less air pollution than old cars, which use up a lot of gasoline.
There are many ways people conserve resources. Car companies are making new cars that run on both electricity and gasoline. They are also changing the way cars that use gasoline work. Now some cars use less. This helps conserve gasoline. Gasoline is a nonrenewable resource. Using less gas also causes less air pollution. This way, air can stay clean for longer. But the easiest way to use less gasoline is to take fewer trips in the car.
Sometimes conserving resources means using a little less of something. Next time you buy something at the store, you could use your backpack to carry it home instead of taking a new paper bag. This way, fewer paper bags are used. Then fewer trees need to be cut down to make them. Ask your mom or dad to bring back the bags they use at the grocery store each time they go. This saves paper too.
Take old paper or plastic bags, or your own backpack, when you go shopping.
One way to help conserve water and keep it clean is to plant trees along riverbanks.
Tree roots grow deep into the moist soil along a riverbank. This makes it harder for soil to wear away in the wind or rain. The trees also help keep soil from sliding down into the water. This kind of conservation helps keep water clean. It also adds more trees to Earth. It keeps the soil healthy too. Clean water and soil are very important to animals that make their homes near rivers.
What We Do with Trash: 
We make many things out of natural resources. Aluminum cans, plastic bags, newspapers, aluminum foil, and glass bottles are all made from natural resources. Many of these things are used every day. What happens to them after we use them? We throw them out in the trash. But where does all our trash go?
We bury a lot of our trash in landfills. A landfill is a place where a giant hole is dug into the ground and covered with a liner. Our trash is put on top of the liner so it does not sink into the soil.
Our trash never really goes away, and we are running out of places to bury it. Some places have tried burning trash instead. But burning trash can cause air pollution.
Ways to Use Resources Again: 
A different way to solve our trash problem is to make less trash. You can help do this every day Maybe you could use empty jars to hold things such as pens and pencils. Or when you have finished drinking a can of juice, do not throw it in the trash. Recycle it.
When we recycle something, it gets changed so we can use it again. For example, you can recycle your plastic juice containers. They can go to a recycling center. There they might be made into plastic parts that will be put in a new computer!
There are separate recycling bins for paper, glass, aluminum, and plastic.
Recycling is the reason people put their trash into different piles. Newspapers get recycled. Plastic, glass, and aluminum get recycled too. These things do not go to a landfill and take up space. They go to a recycling center.
When an aluminum can goes to a recycling center, it is chopped into little pieces. Very hot air takes any paint off the metal scraps. Then these scraps are melted in an even hotter furnace. The melted aluminum is poured into molds, and new cans are made. These cans may end up back at the recycling center once they've been used again.
How to Recycle: 
People have been recycling for a long time. Your parents probably do it, and you can too. When you help with the shopping, you can tell your parents that it is a good idea to pick things with a recycling symbol on the package. This means that the box, jar, or can that the food comes in was made from recycled materials.
Even your clothing can be made from recycled material. Everything from wrapping paper to car tires can be made from recycled goods today.
Look for recycling symbols such as this one when you are shopping.
Remember the three Rs. Reduce the amount of natural resources you use and the amount of trash you create. Reuse as many things as you can. Recycle all the things that you can. This way, you are really helping the planet.
Collect things made of plastic, glass, paper, and aluminum.
All these things can be recycled.
Reduce your trash. Reuse or recycle as many things as possible.
What did you learn?
Are trees a renewable or nonrenewable resource? Why?
Why are coal and oil nonrenewable resources?
Name some things that can be recycled.
In this book you have read about how planting trees can help conserve some natural resources. Write to explain what these resources are and how they are affected.
What happens to trash when it is thrown away? What happens to trash when it is recycled?
Look around your classroom. Everything you see is matter. The tables, chairs, books, and people are matter. So are the tiniest pieces of dirt and dust. Matter is anything that takes up space and has mass.
Everything around you is matter. That includes the air you breathe. You usually can't see the air you breathe. But don't be fooled. Air is matter!
All objects are made of matter. But not all objects are the same. Look around your classroom again. Some objects are big. Others are small. Some objects are heavy. Others are light. Some objects are hard and some are soft.
Each object has its own special properties.
A property is a quality of matter that can be observed. You can observe properties with your senses.
By observing matter's properties, you can learn about how things are different. Touching, smelling, and looking at objects helps you learn about their properties.
Matter comes in three forms. These forms are solid, liquid, and gas. All three forms are made up of particles, or very small parts. The particles are too small for you to see. But they are always moving. How much they move depends on the form of matter.
Are you sitting at a desk as you read this? If so, touch the desk. It's pretty hard, right? The desk is a solid. A solid has a shape that doesn't change. Objects such as walls, lamps, and rocks are all solids. The particles in them are very close together. Solids keep their shape because their particles are so close together.
Milk poured into a glass has a shape. The milk had a different shape when it was in the carton. Why did its shape change?
Milk is a liquid. Liquids change shape to match the space they fill. If you pour the milk into a bowl, it will change shape again. No matter what a liquid is poured into, it will always take up the same amount of space. Only the shape will change.
Compared to solids, the particles in liquids are farther apart. But they are still connected. The particles in liquids move around easily.
Matter can also be a gas. Gases are shapeless. The particles in gas are not connected. They bounce around.
Air is an example of a gas. Blow air into a paper bag. What happens? The bag fills up with the air. The air's pressure pushes out the bag's sides.
Gases will take up as much space as they can. If you let the air out, the bag changes its shape!
Some matter can change forms. Water is liquid. It freezes when the temperature drops below thirty-two degrees Fahrenheit. Water freezes to become a solid ice cube.
Candles, like water, also can change form. Candles start as a solid. Their wax melts when it is heated. When that happens, candles turn into liquid. Both water and candles change forms if their temperatures change enough.
A piece of silver can be broken into smaller and smaller pieces. No matter how small you make them, they will still be silver. Silver is an element. An element is matter that is made of a single kind of particle. Each element's particles are too small to see. Iron, gold, copper, and nickel are all elements.
Elements can be broken into atoms. An atom is a tiny particle of an element. It still has all the properties of that element. One atom of carbon has all the properties of carbon.
There are more than one hundred elements. Each element has its own properties. Elements that have similar properties are sometimes called "families." The periodic table is a table that lists elements based on their properties. Elements listed in the same column have similar properties. Each element gets its own box on the periodic table. This box shows the element's symbol and name.
Mass is the amount of matter an object has. All solids, liquids, and gases have mass. Mass is measured in grams. Grams are the metric unit for mass.
A balance is used to measure and compare the mass of matter. Put some rocks on one side of a balance. Place some feathers on the other side. What happens? The rocks have more mass. Their side of the balance will lower. The feathers have less mass. Their side will rise.
Some objects have more mass than others. All objects and all forms of matter have mass. An object's mass does not change. If it changes shape, or moves to another place, its mass is still the same.
Make a clay horse and record its mass. What if you change its shape to a clay bird? If you measure its mass again, it will be the same if you used all the clay.
Weight is different than mass. An object's weight can change depending on its location.
Volume is the amount of space an object takes up. All forms of matter have volume.
A measuring cup can be used to measure the volume of liquids and solids. The volume of liquids is measured in liters. Liters are metric units. Each liter contains one thousand milliliters.
Pour some water into a measuring cup.
The cup's water level rises to 200 milliliters.
That level is the water's volume. Then place an orange in the cup of water. The liquid rises to 350 milliliters. What has happened? The orange added 150 milliliters to the measure. That means that the volume of the orange below water is 150 milliliters.
Density and Buoyancy: 
All matter has density. Density is a measure of how much matter is in a space. Think about a bag of bricks and a bag of cotton balls. The bags are equal in volume. But the bricks have more mass. The bricks have a greater density than the cotton.
You can learn more about an object's density by observing buoyancy. Buoyancy is how well an object floats. It is a property of matter.
Drop a brick into a pool. Its high density makes it sink. The brick has little buoyancy. What if you drop a cork into a pool? Its low density makes it float. The cork has a lot of buoyancy.
Measuring Properties: 
Matter's different properties can be observed in many ways. For example, you can use a ruler to measure an object's length. A meter is the basic metric unit of length. There are 100 centimeters in a meter. A kilometer has 1,000 meters.
Rulers and tape measures can be used to find the length of common objects. How long is your arm? Is it longer or shorter than your friend's arm? By measuring the length of both arms, you can find out for sure whose arm is longer. Two other properties of matter that can be measured are mass and volume.
Matter can be a solid, liquid, or gas. By observing matter's properties, you can learn more about it.
Did you know that you can combine all three states of matter at once? Gather together a piece of paper, a straw, and paint. The paper and straw are solids. The paint is a liquid. And the air in your breath is a gas. Place a dab of paint on the paper. Then blow through the straw to move it around. You have just mixed three forms of matter! Everyday objects can be more interesting when you study their matter and properties.
What did you learn?
What are the three forms of matter?
If two elements are listed in the same column of the periodic table, what do you know about them?
How do you measure mass? What is the unit for measuring it?
In this book you have read about how density and buoyancy are closely related. Write to explain their relationship. Use examples from the book.
What causes a candle's wax to melt? What is the effect?