Nuclear energy is the most powerful form of energy in the universe.
There are two ways of producing it and both ways release enormous amounts of energy.
  • One way is to split the nucleus of an atom. This process is called nuclear fission.
  • The other way is to join together, or fuse, the nuclei of two atoms. This process is called nuclear fusion and it is happening all the time inside the sun.
In 1938, scientists for first time split the nucleus of an atom. All the nuclear power stations built so far use the heat from nuclear fission to generate electricity. Scientists are still trying to find a safe way of obtaining energy from nuclear fusion. When they discover how to do this, we may have power stations fueled by nuclear fusion.
Nuclear fission takes place when the nucleus of a uranium atom splits, releasing neutrons. These hit other atoms, causing them to split, and so on. This ongoing process is known as a chain reaction.

There are about 420 nuclear power stations in the world. They produce almost 16 per cent of the world’s electricity.
A nuclear power station works in a similar way to an oil-fired or coal-fired power station. The difference between the two types of power stations is in the fuel they use to heat the boilers. Inside a nuclear power station, energy is released by nuclear fission in the core of a piece of equipment called the reactor. The energy heats water in the boiler. The water boils and produces steam. This steam burns the huge turbine wheels, and the turbines drive the generator that produces the electricity.

Nuclear fission must be carefully controlled. The fuel inside the reactor is a metal called uranium. When the nucleus of an atom of uranium is split, the neutrons released hit other atoms and split them in turn.
More energy is released each time another atom splits. This is called a chain reaction.
Inside the reactor in a nuclear power station, the nuclei of the uranium atoms are split.
Nuclear reactors release another kind of energy called radioactivity.
If radioactivity escapes into the atmosphere, it can quickly cause serious damage to humans, animals and plants. This is why a nuclear reactor is sealed inside a shield of reinforced concrete.


When you’re traveling by train or riding along in a bus or car, you can easily spot a power station if you pass one. Many power stations have very tall towers called cooling towers. White clouds pour out of them. These are clouds of condensed water vapor, which is formed by steam as it mixes with cold air.

The power of steam
Power stations that burn coal or oil have three main parts— the boiler, the turbines, and the generator. The power station burns coal or oil to produce heat in its boiler. The boiler is lined with pipes carrying water, which boils and turns to steam. The steam is then piped to huge “wheels” fitted with hundreds of steel blades. These wheels are the turbines.
The steam rushes through the turbines at high speed and turns the steel blades. In a large power station, the steam passes through several turbines until almost all of its energy has been used up. The used steam then cools in the cooling towers and changes back into water. This changing process is called condensation. The water returns to the boiler and is heated up again.

Whether power stations use oil, coal or nuclear fuel, they all produce steam that drives huge turbine wheels.
Some of the heat energy produced by this coal-fired power station is used to make electricity. Most of the heat energy escapes up the tall cooling towers.

Inside the generator
The central rod, or shaft, of the turbine is connected to a coil of wire inside the generator. This coil, or rotor, is pushed around as the turbine wheels rotate. It rotates inside another coil, the stator, which is fixed and cannot turn. The movement of the rotor inside the stator generates electricity.

Fuel for power
Power stations need large supplies of water and fuel. They are usually built near rivers or lakes so a large supply of water is always present. Coal-fired power stations are sometimes close to coal mines so that the coal can be transported easily. Oil-fired power stations are supplied with oil by pipelines.


Why is electricity the most convenient form of energy to use?

  • It is clean.
  • It can travel over long distances along wires.
  • It can easily be changed into other forms of energy, such as heat and light.
  • To use the electricity connected to your home, all you have to do is to switch it on or plug an appliance into an electrical outlet.
The world is full of electrical energy, but most of it is in a form we cannot use. Lightning is one example of electrical energy that we cannot use. We can’t convert the electrical energy in a flash of lightning into useful electricity. Most of the electricity we use in our homes is made by generators at power stations. These generators are really energy converters. They convert kinetic energy at the power station into electrical energy.
The kinetic energy is produced by burning fuel, by moving water, or by wind power.

What is an electricity grid?

One problem with electrical energy from power stations is that it cannot easily be stored. Once the electrical energy has been made, it must travel along the cables and wires to where it is needed. Most power stations are linked to a network of cables called a power pool. When there is a big demand for electricity—for example, for air conditioning during very hot weather—more power stations send electricity into the power pool. When less energy is needed, some of the power stations reduce the amount of electricity they produce. Some countries make more electricity than they need. They sell the spare energy to countries which do not have enough.

Making your own electricity
Do you have a lamp on your bicycle? If you do, this means you may have a simple type of generator, called a dynamo, to make the lamp shine. The dynamo contains a strong magnet which rotates when the bicycle wheel turns. An electric current starts to flow in a coil of wire near the rotating magnet. The dynamo converts the kinetic energy of the turning wheel into electrical energy to light the lamp. You can easily see this working if you turn your bicycle upside down and turn the pedals by hand.
You can make electricity yourself if your bicycle has a dynamo.
The generators in a power station work in much the same way as a dynamo.
Wires carry the supply of electricity from this power station to places where it is needed.


How old is a lump of coal?
This sounds like a trick question, but it isn’t. Coal is millions of years old.
Anthracite, the oldest and hardest coal, is 400 million years old. All those years ago, many parts of the earth were covered with wet, marsh-like areas of land, called swamps. Huge trees, giant ferns, mosses, and other plants grew in these swamps. As the trees and plants lost their leaves or died, the leaves and dead material formed into layers of rotting vegetation. In time, pressure from above packed these layers together to form a layer of soft material called peat. Peat is found throughout the world in swamps and marshes. It can be cut, dried and burned as fuel.
Sometimes, mud and sand were washed over the layers of rotting vegetation, pressing them even tighter together. This made a soft, brown kind of coal called lignite. As more mud and sand piled on top, the vegetation was pressed down even deeper. Movement inside the earth’s crust helped to turn the lignite into hard, black coal. Sometimes, if you look closely at a piece of coal, you can see the outlines of a leaf from a fern that was alive millions of years ago.

Oil and gas
Oil was formed in a similar way to coal. Millions of years ago, small plants and animals that lived in the seas sank down to the seabed when they died. They were crushed under layers of mud and gradually turned into oil. As oil formed, it gave off natural gas. The oil and gas seeped upwards until they reached layers of hard rock and became trapped under the rock.

Coal, oil, and natural gas are called fossil fuels. They were formed from the remains of plants and animals that died long ago.
When these plants and animals were alive, they converted energy from the sun into chemical energy. When we burn fossil fuels, we turn this chemical energy back into heat energy and light energy. In other words, we are releasing from these fuels the energy that first came to earth from the sun millions of years ago.


  • Sunlight is so strong that it can damage your eyesight and even blind you.
  • Never look directly at the sun through a telescope, binoculars, or sunglasses.

Did you know that the sun is really a star?

It looks much larger than the stars we see in the sky at night. Although many of those stars are even larger than the sun, they look smaller because they are even farther away from the earth.
All stars produce huge amounts of energy. Each star is like a powerhouse of energy. In one second, the sun, for example, produces 4 million short tons (3.6 million metric tons) of energy. Without the sun’s energy there would be no life on earth. The earth would be completely dark and freezing cold.

Heat energy travels from the core of the sun to its surface. Energy is released from the sun’s surface as electromagnetic radiation.


The sun is a huge ball of hot substances. The hottest part is in the center, or core. Here, the fierce heat causes atoms of hydrogen to join together in the process called nuclear fusion. During nuclear fusion, huge amounts of energy are released. This energy flows outwards from the core to the surface of the sun.
The surface of the sun is like a sea of continually exploding gases and boiling liquids. Much of the sun’s energy is heat and light, and this travels out, or radiates, in all directions. The sun is the source of almost all the energy we use.

A fountain of gas flares up from the surface of the sun, reaching as far as 992,000 miles (1,600,000 kilometers) into space.

Will the sun burn itself out?

If the sun is producing so much heat and light, why doesn’t it burn itself out like a coal fire or a match? The answer is that it will burn itself out, one day. It will swell up into a giant red star and use up the rest of its fuel. But don’t worry—that day is about 5 billion years away!


Have you ever taken a spoon out of a mug of hot cocoa or tea or some other hot drink?
Did you find that the spoon was too hot to hold, so that you had to drop it?
Did you burn your fingers?

If you have never done this, don’t try it now.
 But if you have done this, then you found out the hard way that heat can travel through some solid materials, such as metals. When heat travels in this way, we say that the heat is conducted. In the hot drink, the heat is conducted from the liquid into the metal spoon.
Why was the handle of the spoon so hot?
Atoms in the bowl of the spoon move faster and bump harder into each other as they heat up. The faster the atoms vibrate the hotter the spoon becomes. The atoms in the lower part of the spoon then bump into the metal atoms a little farther up the spoon. These atoms then bump against their neighbors even farther up and start them vibrating. Soon, all the atoms in the spoon are vibrating faster.
When the handle of the spoon is cold, the atoms in the metal vibrate slowly.

When the handle of the spoon is hot, the atoms vibrate quickly and bump into each other.
A material that allows heat to travel through it, like the metal spoon, is called a conductor. Some materials are better conductors of heat than others. Metals like iron, steel, and copper are good conductors. They also allow electricity to flow easily through them. Other materials, such as rubber, wood, glass, and some plastics, are poor conductors. A material that does not conduct heat or electricity easily is called an insulator.

Protection from heat and cold

Insulators are useful materials. The handle of a saucepan, for example, is often made of plastic or wood. This stops the conduction of heat from the pan to the handle. Fire fighters wear clothes made from another good insulating material called fiberglass. The fiberglass prevents the heat of a fire from reaching the fire fighter’s body.
Air is a good insulator, too. This is why we wear wool clothes to keep warm in cold weather. Wool traps plenty of air between its fibers. Special insulated underwear provides air spaces that help retain body heat. Can you think of any other ways m which we use insulators to keep away heat, or keep it in?


Do you know that you are working when you are playing?

To a scientist, work is any kind of action that uses energy.

Energy is needed to do all types of work—for example, to throw a ball into the air and to catch it. Energy is needed because something does not move unless you push or pull it. And it doesn’t stop moving unless something else slows it down. When you catch a ball, your hand can feel the ball pushing to continue moving. Inertia is a basic characteristic of an object as it continues to stay at rest or continues to move.
If you want to start moving something or stop it from moving, you need to push or pull it. These pushes and pulls are called forces. Forces are needed to overcome inertia. Forces are produced by applying energy. The more force applied, the more energy used and the more work done.

Energy for lifting

When you lift a heavy box, potential energy changes to kinetic energy in your muscles. You use more energy and do more work when you move a heavy box than when you lift a lighter box for the same distance. You do more work when you lift a box up to a high shelf than when you lift it onto a low shelf. If you carry a pile of books weighing 22 pounds (10 kilograms) up a flight of stairs, you do twice as much work than if you carried an 11-pound (5-kilogram) pile up the same flight of stairs. Since work is equal to force times distance, the energy you use is equal to the weight of the books times the distance you moved.


Every form of energy can change into another form of energy.
Coal is a fuel that contains stored chemical energy. When coal burns, the chemical energy inside it changes into heat energy.
Energy may change in form, but it can’t be made out of nothing, and neither can it be destroyed.
A power station does not create the electrical energy we use in our homes.
The power station changes the chemical energy of the fuel into electrical energy.
 When we use electricity, we don’t destroy the electrical energy. Instead, we change this energy into another form of energy, such as heat or light.

Energy converters

Imagine you are on a camping trip. You feel tired at the end of the day and want a hot drink. You’ve taken with you some soup and matches. You’ve also brought an aluminum saucepan. Woods nearby supply you with dry twigs.
When you make a camp fire, heat the saucepan, and drink your soup, a scientific process takes place. By setting fire to the wood, you change, or convert, the stored chemical energy in the twigs into heat energy. This heat energy boils the soup. After you have drunk the soup, your body turns the chemical energy in the soup into potential energy. Your body will turn it into kinetic energy for use on the camping trip.

Your body is an energy converter. Some of the chemical energy you take in as food is converted into potential energy and then into kinetic energy. Some of the chemical energy is converted into heat energy to maintain body temperature.

Converting energy in the home

We need to change one kind of energy into another in our homes. A toaster changes electrical energy into heat energy. An electric light bulb converts electrical energy into heat and light energy. If you look around your house, you’ll soon realize there are a number of energy converters at home.

The solar cells on this light aircraft convert the sun’s rays into electricity.

Old and new energy converters

For thousands of years, people have made many different kinds of energy converters. One of the earliest kinds was the waterwheel.

Moving water pushed the blades attached to the wheel, and this made the wheel turn. Waterwheels were often joined to large millstones. As the waterwheel turned, it turned the millstones, which then ground corn or wheat. The waterwheel converted the potential energy of the falling water into kinetic energy for grinding the foodstuff.
A solar cell is a modern kind of energy converter. It converts light energy from the sun into electrical energy. Solar cells can be used to make radios and telephones work. Solar cells are also used to operate telecommunications satellites which orbit the earth.

Electromagnetic Energy Definition - What is Electromagnetic Energy?

What is Electromagnetic Energy?
What do you think the air contains?
It contains millions of tiny, fast-moving particles.

Waves of energy pass through the air, too.
This kind of energy, called electromagnetic energy, is made of vibrations of electricity and magnetism. 
There is a whole range of different electromagnetic waves.
Some electromagnetic waves vibrate very fast. These waves have a great deal of energy.
Other waves vibrate slowly and have less energy.
Some of the most energetic electromagnetic waves are called X rays.
These are used in hospital machines to photograph the inside of a person’s body.
When an X ray photograph is taken, your body receives a very short burst of X ray energy.

Electromagnetic Energy Examples - The Electromagnetic Spectrum

A schematic of how electromagnetic energy is attenuated as it goes from the sun (source) to a sensor after interaction with the Earth

A schematic of how electromagnetic energy is attenuated as it goes from the sun (source) to a sensor after interaction with the Earth

The speed of electromagnetic waves

There are many different types of electromagnetic waves, but in one way they are all similar.
They travel through space at the same speed as light—186,282 miles (299,792 kilometers) per second. 
  • Electromagnetic waves can travel around the world more than seven times in one second.
  • When you watch a sports telecast that is a live transmission from 3,100 miles (5,000 kilometers) away, you are seeing the picture at almost exactly the same moment as the athletes are actually running.
  • It takes about eight minutes for light waves from the sun to reach us on earth.
  • Other stars are even farther away. It takes light waves about four years to travel from the closest stars to the earth. Scientists say that these stars are light years away from the earth.
  • Light and heat energy travel through the air as different kinds of electromagnetic waves. 
  • Sunlight travels to earth as light waves.
  • The heat from the sun travels as infra-red waves.
  • Radio waves bring us radio and television.

Sound Energy Definition - What Is Sound Energy?

Have you ever heard a jet airplane when it is getting ready to take off?
The noise that the plane makes is sometimes so loud that you cannot hear any other noise.

Sound is a type of energy.

Sounds are produced when an object vibrates.

When this happens, the air around the object also vibrates. These vibrations in the air travel as sound waves. A jet engine makes a great deal of sound energy. The engine sounds loud when it is close, but you can sometimes hear the noise when the plane is even several miles away from you.

People who work on airport runways need to protect their ears from the noise of the aircraft engines. They wear protective gear over their ears.

Rippling vibrations

Think of the ripples on a small lake when you throw a pebble into the calm water. If the lake is big enough, the ripples become smaller and smaller until they disappear altogether before they reach the edge of the lake.

In the same way, sound spreads out in waves from the place where it is first made.
The sound waves, like the ripples in the lake, become weaker the farther they travel.
The energy of the waves becomes more spread out.

Scientists use units called decibels to measure the intensity of sound.

The sound of whispering measures about 20 decibels.
The noise from a jumbo jet taking off at close range measures about 140 decibels.
If sound measures more than 140 decibels, it is dangerous and can seriously damage your hearing.
The sound of a purring cat is soft and gentle, but the noise made by a jumbo jet is loud and harsh.


“On your marks!
Get set!
Go! ”
These are the orders the starter shouts when you take part in a running race.
When you are running, your body has a lot of kinetic energy, the energy of movement. When you are “on your marks,” you use a small amount of energy. Most of your energy is stored, or saved up, ready for the running of the race.

Energy that is stored and waiting to be used is called potential energy.

Potential energy is often linked to work that has already been done. Take a ball and place it on the floor. Now put the ball on a high shelf. The ball has more potential energy when it is on the shelf than it has on the floor. The ball has gained this extra energy because work was done when the ball was placed on the high shelf. Do you know how to turn the potential, or stored, energy of the ball into kinetic, or moving, energy?

How is energy stored?

An archer’s bow has potential energy when it is bent. When the archer releases the bow, this potential energy changes into kinetic energy, and the arrow shoots forwards. When you wind up a clock, potential energy is stored in the clock’s spring. This energy changes into the kinetic energy that makes the clock work.

The potential energy of this archer’s bent bow will turn into kinetic energy when the archer releases the bow’s string.


We use energy all the time, even when we are asleep.
We need energy for our body to work.
We need energy to keep us warm.
When the weather is cold, or when we take part in sports, we need extra amounts of energy to help our body and muscles work harder.
Our energy comes from the food we eat.
 Food contains chemical energy. As the food is broken down, our body uses the energy to keep warm and to do work.

Do you know which foods contain large amounts of chemical energy?

Scientists have been able to work out the amounts of chemical energy in different foods.
The amount of energy in food is measured in units called calories.
A plateful of lettuce, for example, has few calories and therefore very little energy.
Rice and bananas contain much more energy.
But an equal amount of ice cream contains even more!
When you eat food, it travels through your body to your stomach and intestines.
Special chemicals called enzymes in your stomach break down the food into different substances that your body can use. We call this breaking-down process digestion. The substances from food that produce energy for your body most efficiently are called fats and carbohydrates. Fats, like butter and oil, and carbohydrates, like bread, potatoes, and sugars, are high in calories.

Our body needs energy

Different people need different amounts of energy from their food. A person doing heavy work, like digging or sawing wood, or an Arctic explorer in the freezing cold needs a lot more energy than an office worker. Active children need about the same amount of energy as adults doing light work. Older people usually do less work and move around more slowly, so they need less energy.
It is important to eat only as much food as your body needs to keep your weight and energy at a comfortable level. It is also important to eat the right kinds of food. Besides fats and carbohydrates, your body also needs proteins such as fish, meat, and cheese. Protein is necessary for the growth and maintenance of body structures.


Chemical energy is one kind of energy that is “locked up” inside atoms and molecules.
Another kind is nuclear energy.
In the center of every atom is the nucleus. 
This is made of tiny particles called protons and neutrons.
Protons have a positive electrical charge.
Neutrons have no electrical charge.
The nucleus is surrounded by electrons, which have a negative charge. The positively charged protons and negatively charged electrons attract each other. Each atom is held together by this force of attraction.

  Splitting atoms

Most atoms can be arranged into different groups, to make different substances. The atoms of a few metals can be changed, or split, to make new, different atoms. The nucleus of an atom of a metal called uranium can be split into two.
This is called nuclear fission. The word “fission” means breaking apart.
When the nucleus of a uranium atom is split, some of its neutrons escape. These neutrons crash into other uranium atoms, causing them to split. As the nucleus of the atom is split, it releases huge amounts of heat. In a nuclear power station, this heat energy is used to produce electricity.

Fusing atoms

The nuclei of the atoms of the gas hydrogen cannot be split, but they can be squeezed together.
This process is called nuclear fusion. The word “fusion” means joining together.
A type of hydrogen gas called deuterium is heated to extremely high temperatures. The deuterium atoms crash into each other and form heavier elements. This process releases large amounts of energy. Scientists are trying to find a way of using nuclear fusion in power stations because it will be one of the cheapest and cleanest ways of producing electricity.
The sun’s energy comes from the nuclear fusion of hydrogen atoms. The hydrogen atoms in the sun continually crash into each other and fuse, making larger atoms of helium gas.
An atom is made up of three different types of particles—protons, neutrons, and electrons. The protons and neutrons are crowded into the nucleus near the center of the atom. The electrons go around the nucleus at fantastic speeds.

The photograph shows the mushroom-shaped cloud that rises up into the air following a nuclear explosion.


Have you ever been to a display of chemical energy?
You probably have, but you called it something else. At a display of chemical energy, there are usually many different colored lights and a lot of noise.
Rockets shoot up into the sky.
Firecrackers make loud bangs.
Pinwheels spin around very quickly.
Stars shoot out of Roman candles.
Yes, fireworks use chemical energy. 
Fireworks are made of a special exploding powder called gunpowder, as well as other explosive chemicals. These chemicals contain lots of energy. When gunpowder burns, it releases large amounts of different gases. These gases are released at great speed. So the energy escapes quickly and with lots of noise into the air. The colored lights of the fireworks are made by burning other chemicals.

When a firework has finished burning, all that is left inside is some black powder which does not burn. The high-energy chemicals in the gunpowder have been changed into high-energy, moving gases.
These gases have created kinetic energy of motion and sound. The change that takes place inside the firework is called a chemical change.

Chemical change

Fireworks are just one example of a chemical change.
There are many more examples taking place all around you. Car engines use chemical energy, too. High-energy molecules of gasoline are burned inside a car engine. The gasoline molecules turn into gas molecules that produce kinetic energy.
Chemical energy can also be produced without burning. Animals and humans use chemical energy in food. They use the chemical energy to work and keep warm. Light energy from the sun can also be changed into chemical energy.
This happens when sunlight reaches the leaves of plants.
The plants trap this energy and use it to make a special substance called glucose. The glucose contains chemical energy. Living things can get energy from glucose.

Car engines run on a mixture of gasoline and air. When this mixture comes into contact with an electric spark, heat energy and kinetic energy are produced.


Do you know what you are made of?

One answer is that you are made of flesh, blood, and bone.
Another answer is that you are made of atoms and molecules. Atoms are tiny bits of matter that join together to make everything in the world. An atom is over a million times smaller than the thickness of a human hair. Atoms come together to form groups called molecules. Powerful microscopes produce pictures of atoms and molecules. We cannot see them directly.

What is kinetic energy?

Atoms and molecules are in motion all the time. They have energy called kinetic energy.
“Kinetic” comes from a Greek word meaning to move.
In a solid object like a bar of iron, the atoms are packed close together.
When the iron bar is cold, they vibrate only a little.
When the iron bar is heated up, the atoms start to move faster and faster.
The quicker the atoms move, the more kinetic energy they have.
If the iron bar becomes hot enough, the atoms have so much kinetic energy that they can separate from each other.
Then the solid iron melts and becomes a liquid.


  • How do you keep cool in your house?

  • What sort of light do you use at night?

  • What appliances do you have in your home?

    Anything that gives you heat or light uses energy.

Household appliances use energy. In your notebook, make a list of all the things in your kitchen that use energy. What kind of energy do you think each appliance uses?
Most homes receive a supply of electricity. The electricity travels along cables and wires from a power station. At the power station, electricity is usually made from the energy released by burning fossil fuels, or by using nuclear fuel or waterpower.
Fossil fuels developed from the remains of prehistoric plants and animals. 
These fuels include coal, natural gas, and petroleum, from which we get oil. Wood, also, is often classified as a fossil fuel.
Besides electricity, fossil fuels are also used as a source of energy in our homes. Wood, coal, and oil can be burned to give heat. Natural gas can be burned for heating and cooking. Oil lamps and gasoline lanterns can be used as a source of light.
Other sources of energy in the home include solar energy and wind power.
Solar energy is energy from the sun, often gathered by solar panels. Solar energy can warm a house or heat up water. Wind power is often impractical unless there are strong, steady winds.

Fossil fuels are called nonrenewable sources

- of energy because, once they have been used up, they cannot be replaced. One day, all the coal, natural gas, and oil on earth may be used up. There will then be no more available.

Sources of energy that can be used over and over again are called renewable, or inexhaustible, sources.

Solar energy and forms of solar energy, like wind power and water power, are renewable energy sources. No matter how much we use them, there will always be plenty more.

Renewable and Nonrenewable Energy Resources

The world is full of movement.
Trees move in the wind.
Aircraft fly in the air.
Ships sail on the sea.
People and animals move around.
None of these things can move without energy. Living things and machines need energy in order to work.

Where does energy come from?

Almost all energy comes from the sun.
The sun’s energy changes into other kinds of energy when it reaches the earth.
The sun’s energy is even in coal and oil.
Long ago, the sun gave its energy to plants and animals. When they died, their bodies slowly turned into oil and coal over millions of years.
Power stations then change the energy in coal and oil into electrical energy.
Without the sun providing energy, there would be no life on earth.

Energy sources

How do you keep cool in your house? 
What sort of light do you use at night? 
What appliances do you have in your home? 
Anything that gives you heat or light uses energy. 
Household appliances use energy. In your notebook, make a list of all the things in your kitchen that use energy.
What kind of energy do you think each appliance uses?
Most homes receive a supply of electricity. The electricity travels along cables and wires from a power station. At the power station, electricity is usually made from the energy released by burning fossil fuels, or by using nuclear fuel or waterpower.
Fossil fuels developed from the remains of prehistoric plants and animals.
These fuels include coal, natural gas, and petroleum, from which we get oil.
Wood, also, is often classified as a fossil fuel.
Besides electricity, fossil fuels are also used as a source of energy in our homes.
Wood, coal, and oil can be burned to give heat. Natural gas can be burned for heating and cooking.
Oil lamps and gasoline lanterns can be used as a source of light.
Other sources of energy in the home include solar energy and wind power.

Solar energy is energy from the sun, often gathered by solar panels. Solar energy can warm a house or heat up water. Wind power is often impractical unless there are strong, steady winds.

Fossil fuels are called nonrenewable sources

- of energy because, once they have been used up, they cannot be replaced. One day, all the coal, natural gas, and oil on earth may be used up. There will then be no more available.

Sources of energy that can be used over and over again are called renewable, or inexhaustible, sources.

Solar energy and forms of solar energy, like wind power and water power, are renewable energy sources. No matter how much we use them, there will always be plenty more.

Who invented the airplane?

Who invented the airplane?

The thought of flying like a bird, is among the oldest of human dreams.
One of the most famous legends of the ancient Greeks, talks about Icarus, who glued wings with wax to himself and soared into the sky!
However, while he was flying toward the sun, the wax melted, and Icarus plunged into the sea and drowned. Icarus has become a symbol of man's aspirations to reach the celestial nowhere.
Leonardo Da Vinci, one of the greatest artists of the Renaissance, drew sketches for some kind of flying machine that will run on manpower. Also many other artists and dreamers, hundreds of years ago dreamed of flying “like a bird”.
The oldest aircrafts did not had anything that would move.
These in fact, resembled more like a huge dragons or boats, and during the 19th century with them were conducted numerous experiments.
But then no one has managed to invent a machine heavier than air, which would have its own drive.
Some, indeed, even doubted that such a machine is even possible to make.
The first man who proved that it is indeed possible was Professor Samuel Langley, from the Smithsonian institution in Washington. He made two machines 4.5 meters long and 3.5 meters wide, which were powered by steam engines from one and a half horsepower. In 1896 these two models successfully flew but in 1903, during a test flight, one machine crashed on October 7th, 1903.
Soon after on December 17 1903, the American brothers Orville and Wilbur Wright were able to successfully fly for the first time in a machine heavier than air, which had its own motive power.
In Kitty Hawk, in North Carolina, they made a flight of 36 meters for 12 seconds, and when the second flight of 260 meters for 59 seconds.

Thus the plane was born.


Imagine if you find yourself into an empty space at the height of 4-5 miles above the Earth, and yet you have landed on the ground as if you jumped from fence 3 meters high.
This we can do with a parachute!

The parachute is just a big umbrella, that with its shape and surface, due to air resistance, slows the decline and fall of man through the air, slowly and slowly enough, that he does not hurt himself when he hits the ground.
The parachute is probably the oldest invention of slowing the fall.
Leonardo Da Vinci made a sketch of a parachute in his notebook in 1514.
Faust Vrančić published in 1595 a description of a usable parachute.
It is believed that the first man who used a parachute was the Frenchman Blanchard. In 1785 from a flying air balloon he parachuted a dog in a basket.
Jean-Pierre Blanchard claimed that he also parachuted from a balloon in 1793 and that during the descent to Earth, he broke his leg.

Another Frenchman, André-Jacques Garnerin, became famous as the first man who regularly paratrooped. For first time he publicly performed in Paris on October 22nd, 1793, and this is when he successfully jumped from a height greater than 600 meters.His parachute had a shape of umbrellas and was made of white cloth which was used for making sails, with diameter of 7 meters. At the center of the dome was a wooden reel of about 25 centimeters, with a hole in the middle, which allowed the air to come out from the dome.
The first successful parachute jump from an airplane in flight was performed in 1912 by the Captain Berry in Saint Louis, Missouri. 
During 1913 and 1914 there were many discussions if whether to use the parachutes to rescue the pilots from the plane. At the moment when the First World War started, this question has not yet been clarified. There was a problem in determining the size of the parachute, and in addition there was a fear that the pilot will not be able to jump out of a plane, without entangling the parachute.
In 1919 the U.S. military has embraced the seat type parachute as part of compulsory aviation equipment.

History of Helicopters - Who Made the First Helicopter?

People for long time have dreamed of a flying machine that could rise from the ground right up. Leonardo Da Vinci around year 1500, made a drawing of giant helicopter, which looked like a screw.
Leonardo never attempted to make this helicopter, because he had no engine.

In France in 1783 a toy helicopter was presented, named "Chinese tern", although no one knew
from where this device actually originated. In 1796 George Kelly experimented with similar Chinese terns, and gave a blueprint for steam helicopter.

Over the next hundred years, many have tried to construct a helicopter. Some of these projects were fantastic, others almost practically feasible, but only a few helicopters took off.
The problem was the lack of powerful engine that could lift the helicopter. During the First World War, when such engines were made, it has become possible to construct helicopters that were able to loft a man above the ground.
Designer Igor Sikorsky made two helicopters in 1909th and 1910th. Toward the end of 1917, two Austro-Hungarian officers constructed a helicopter designed for observation of the front, a task that was previously carried out by air balloons. This helicopter was able to repeatedly lift up to greater heights, but in all ended there.
Work on the construction of the helicopter continued in many countries, but without any major success. However in 1936 news came from Germany that the company “Focke-Wulf” managed to produce a good helicopter. This helicopter in 1937 managed to fly long distances at speeds of around 110 kilometers per hour and at altitudes greater than 3,300 meters.

In year 1940 the designer Igor Sikorsky demonstrated his helicopter which could be used in the practice, which was supplied to the U.S. Army in 1942.