Anything which has energy can do work. It must be able to push or pull something. Steam has energy. Moving air has energy. Flowing water has energy. Hot gases from a flame have energy.
            Anything which is moving can push something else. Anything which is moving has energy.
            The push or pull is the force. When the force moves something, work is done.
            We sometimes cook with heat from sunlight. Scouts and other campers use sun cookers for outdoor cooking. There are also sun ovens in which bread, meat, and other foods can be baked. Both of these have a shiny part that collects and focuses sunlight. The sunlight changes to heat energy and cooks the food.
            In the daytime the Sun shines on our side of the Earth. The Sun’s energy warms us all day long. Soil, water, air, rocks, and buildings are heated by the Sun. The Sun shines on the whole Earth. Some parts get more heat and some get less heat.

 

Plants Capture Sunlight

A plant’s food is made in its green leaves. Sunlight shining on the leaves gives a plant the energy it needs. Without light energy the green plant can make no food.

 

Animals and the Sun’s Energy

Some scientists explore deep, dark caves. They find certain strange animals there. They find salamanders, crayfish, and spiders that live in complete darkness. Most of these animals are blind. They feel their way along. They catch food by using their sense of touch.
            There are other scientists who explore the deep, dark parts of the oceans where they find many kinds of strange fishes. These fishes live where the sunlight never reaches.
            On land, there are kinds of termites that look like large, pale ants. These termites spend their lives in darkness. When they travel, they tunnel through the soil. They chew their way through wood. Termites cause a lot of damage.
            All animals need food. They cannot make their own. Only green plants that grow in sunlight can make food. Without the food from green plants, no animals can live. Some animals feed on plants. Other animals feed on the animals that fed on plants.
            Even the animals that live in dark caves feed on dead plants and on animals that fed on plants. The dead plants once grew in sunlight. When they died, they fell or were blown into the caves. Came animals live on food that had been made in the leaves of these green plants that once grew in sunlight.
            In the parts of the ocean where the sunlight cannot reach, fishes feed on ocean animals that have fed on tiny green plants. These green water plants grow where sunlight can reach them. They use energy from the Sun to make food.
            Termites the never see the Sun feed on wood of green plants that grow in sunlight.
            Even the animals that always live in darkness depend on sunlight. Without energy from the Sun, the animals can have no food. Without energy from the Sun, green plants cannot grow.

 

Energy Right from the Sun

            A bulb with spinning vanes is called a radiometer. The vanes of a radiometer are like the arms of a windmill. The arms of a windmill are turned by the wind. The vanes of a radiometer are turned by energy from the Sun.
            Energy from the Sun is called solar energy. The word solar comes from “sol”, an old word for “the Sun”. solar energy turns the vanes of a radiometer. Solar cells are made of a special kind of material. Energy from the Sun makes electric energy in the solar cells. Electricity from solar energy can make a solar radio play.
            Solar cells do not wear out as dry cells (batteries) do. The solar cells get energy whenever it is in sunlight. Large solar batteries are used to change solar energy into electric energy. The electric energy can be stored for future use or sent through telephone wires.
            A solar battery has many solar cells. The battery is made up of rows of thin strips of special material. When the Sun shines on the strips, solar energy is changed to electric energy.

 

Television from Outer Space

            In 1962 television watchers had a new experience. They saw the first programs that came from a space station. Programs that were broadcast in France, England, and other countries were picked up by Telstar, a space satellite. Telstar then relayed the programs to television sets in the United States and other countries. It was the first time a space satellite was used in this way.
            It takes a great deal of electric energy to pick up and relay television programs. The Sun shines on satellites just as it shines on the Earth. There are 3,600 solar cells in Telstar. These solar cells change solar energy to electric energy. The scientists who invented Telstar’s solar cells believe that the cells will last for many, many years.
            Before Telstar was launched into space, other satellites had used solar energy. The solar energy that is changed to electric energy can also send radio signals back to Earth.

Wind

            No one knows who first thought of a way to put the wind to work. Perhaps it was a man who stood up in his little log boat and felt the wind pushing against his back. Perhaps he thought of putting an animal skin between two sticks to catch the wind.
            Once, whole fleets of sailing ships were driven by the wind. There are still many sailing boats. But now most of these are used for fun.
            On land, too, we can put the force of the wind to work. We can catch it in the blades of a windmill. The wind whirls the blades and the blades do the work of turning a machine. The machine can be one that grinds grain, pumps water, generates electricity, or does some other kind of useful work. This is easier than using muscle energy.
            Heat energy from the Sun warms the Earth. Some places get hotter than others. The air above the hot places gets hot too. As the air gets hot, the molecules move faster and farther apart. The hot air rises, and the colder air blows in to take its place. As the hot air goes higher, it cools off. Then down it comes, and more hot air goes up. The Sun’s heat makes air move.
            We could not live without energy from the Sun. the wind would not blow without energy from the Sun. we could do no work without energy from the Sun.

 

Water

            Moving water has plenty of energy and force to move things. It can push heavy logs. It can push big boats. It can push the blades of a water wheel and make the wheel turn. Water wheels were used for turning saw blades. Water wheels have been used to do other work, too. They have been used to grind corn, or pump water, or weave cloth. A big water wheel needs the force of a large stream of water. That is why mills had to be built near rivers. Any factory whose machines were worked by a water wheel had to be near plenty of flowing water.
            Rain and snow fall, and the water collects in high places. It runs downhill in rivers. A huge dam built in the path of a river holds the water back. The water, piled high behind the dam, forms a lake. Energy is stored in the deep, still water of the lake. We can call the energy in the lake stored energy.
            There are places in the dam that can be opened. Where the dam is opened, the water rushes out with a great roaring sound. It falls down, down over the dam. When the water moves, the energy in it changes. The stored energy changes to energy of motion. Energy of motion turns mighty wheels.
            Hoover Dam is only one of the big dams in the United States. Day and night the wheels turn around to supply electric energy. Rivers and other bodies of water have a great deal of energy.
            What happens when the Sun shines on a puddle? Heat from the Sun changes the water to water vapor. The water vapor goes into the air. Some of it goes up high and forms clouds. Raindrops fall from the clouds. Gravity pulls them down to the Earth. The water keeps falling downward from high places. Rivers flow downhill. Water rushes over cliffs and dams. Gravity makes the water flow from high places to low.
            All the energy from moving water depends on the Sun. if the Sun stopped shining, no clouds would form, no rain would fall. There would be no way that water could get uphill for gravity to pull it downhill again. There would be no more energy from rivers and waterfalls.

 

Steam

            In some places there is no steady supply of water to turn machines, so steam is often used instead of water.
            Steam can push with great force. Steam can hit the blades of a wheel and make it turn. Such a wheel is called a steam turbine.
            Long ago, when people found that they could use the energy of steam to do work, they tried many ways of using this energy. One of these ways was building turbines with single wheels. These early turbines did not work well. Now we build them with many wheels. These turbines have a cover around the wheels to keep the steam pushing against the blades.
            Steam is water in the gaseous state. It is hot. Its molecules are moving very fast and have a great deal of energy. This kind of energy is called heat energy. Heat energy changes water into steam.
            Steam takes up more space than the water from which it came. Its molecules are farther apart and move much faster. They can push the blades of a steam turbine and make it turn. The hotter the steam, the more push it has.
            The heat energy for making steam comes from burning fuels such as coal, oil, wood, or gas.

   

Fuels

            A great deal of energy is stored in fuels. Wood is a fuel. Coal, gas, and oil are fuels. Candle wax is a fuel.
            Do you make energy when you burn a candle or some other fuel? It may seem so, but you cannot make energy. You can only change energy that is already there. You can change it into the kind of energy that you need and use.
             You can get energy from candle wax or another fuel only because energy is already stored there. Candle wax is made from oil found in the ground. Scientists think this oil comes from tiny plants and animals that lived long, long ago. These plants and animals used the Sun’s energy to live and grow. As they grew, they stored some of the Sun’s energy.
            Year after year for many millions of years, plants and animals have lived and died. In some way the dead plants and animals were slowly changed, and the oil in them was trapped in the ground. Scientists are not sure exactly how all of this happened. They believe that the energy in oil comes form things that once lived and grew in sunlight.
            Other fuels, like coal and wood, come from things that lived and grew in sunlight. The Sun’s energy is stored in them too. When a fuel burns, you get heat and light. Sometimes those are the kinds of energy that are needed. At times, heat energy is used to move things. In an automobile engine, heat energy from the fuel (gasoline) is used to move the automobile. In rockets, the energy in fuel shoots a satellite into space.

Nuclear Fuel

            Scientists have made a new kind of fuel, nuclear fuel. This fuel is much better than other fuels in two important ways:

1. Only a tiny amount is needed. A piece the size of a golf ball can send a large ship across the ocean! This leaves more room for freight.
2. Nuclear fuel gives off heat without burning, so it does not need oxygen from the air.

            Nuclear fuel, coal, oil, wood, and gas—all of these give heat energy to make steam. The steam spins a turbine that does work.