What are Precious Metals?

We sometimes call valuable metals, such as platinum and gold, precious metals. Platinum is the most valuable metal in the world. It is called a catalyst because it produces a chemical reaction in other substances without itself changing. Platinum is more expensive than gold and is used in many industries. Another metal, iridium, is often used as a hardening agent for platinum.
Gold is the third most valuable metal after platinum and iridium. It can be rolled and stretched more than any other metal. Gold is used to make jewelry and some electronic equipment. Copper is often added to gold to make it harder.
Another precious metal is silver, which loses its shine, or luster, when exposed to the air. Silver must be polished to remove any stains. The photographic film in your camera contains silver, and many ornaments and pieces of jewelry are made of silver.

How are Metals Formed?

How are Metals Formed?

Everything on earth is made up of a combination of building blocks called the chemical elements. 
There are 93 different elements in nature, and most of these are metals. 

Most metals can combine with other chemical elements to form compounds.
These compounds are called minerals when they are found in rocks and soil.
Most minerals grow in liquids, sometimes forming where molten rocks from beneath the earth's crust cool and harden. These metal-containing rocks are called ores.
The large iron ore deposits in Kiruna, in northern Sweden, were formed in this way.
As the molten rocks cool, a mixture of minerals, gas and hot water forces its way into cracks in the rocks. This mixture also cools and hardens to form thin lines that are rich in metallic minerals like lead, copper and zinc.
Some metal elements do not combine easily with other elements.
These metals, like gold, silver and platinum, occur naturally in the earth's crust as small grains, or as larger lumps of metal.
Falling rain and rivers wash these metals out of rocks on the earth's surface.
The heavier metals drop in one area and form placer deposits.
When these deposits occur on river beds, special dredgers sort the metals from gravel deposits.
 Powerful water jets are used to break up dry placer deposits.
The gravel is washed and separated from the metal ore.

Ocean Mining - What is Ocean Mining?

What is Ocean Mining?

Deep down on the seabed, there are fist-sized lumps, or nodules, that contain lots of minerals.
The nodules are made up of layers, like an onion.
They are found in areas where many sea creatures live.
The sea creatures collect and store minerals in their bodies.
When they die and sink to the bottom of the sea, the minerals in their bodies are left in the mud after their bodies have decomposed.
These nodules usually contain iron and manganese, which are used to make hard steel for tools.
Some nodules contain valuable minerals like cobalt, nickel and copper.
It is more difficult and expensive to extract minerals from the sea than from the ground.
But the reserves of minerals on land are quickly being used up. So one day soon we may need to use the sea's resources.
Special machines to mine the nodules on the seabed can be developed and will probably work by remote control.
They will most likely come into use as soon as it is economical to mine the seabed.

What is a climate?

What is a climate?

The weather where you live may be sunny one day and cloudy the next, or dry during one season and wet during another.
Over several years, there's a pattern to these daily and seasonal changes in the weather, wherever you live. This pattern of weather over a period of time is called a climate.
Scientists who study climates are called climatologists. 
They say that the climate varies according to three things — the way the sun's rays reach the earth, the amount of land and sea nearby, and the height of the land above sea level.

The earth is marked into horizontal sections by invisible lines called lines of latitude. 

A main line around the middle is called the equator. 
Two lines of latitude north of the equator are special and are called the Tropic of Cancer and the Arctic Circle.
Two lines of latitude south of the equator are the Tropic of Capricorn and the Antarctic Circle.

You can see that the sun's rays are more concentrated at the equator than anywhere else on earth.
So the countries near the equator are the hottest in the world.

Near the equator, the earth's tilt causes the sun's rays to shine more directly.
The direct sunlight provides enough energy to heat up land and water. In the polar regions, an equal amount of rays is spread over a wider area since the rays meet the earth's surface at more of an angle.
The angle of the tilted earth causes the rays to pass through more atmosphere at polar regions, losing heat along the way.
Energy from the sun warms the ground, and some of this heat is reflected back into the air. As the warm air rises, it cools down. Places that are high above sea level, such as mountains, have cooler climates than places lower down.
Energy from the sun warms the oceans, rivers and lakes, turning some of the water into vapor. This vapor rises to form clouds, and then falls back to earth as rain, sleet, hail or snow.
So places near the coast have wetter climates than places inland.

How to make a Hygrometer?

How to make a Hygrometer? 

When you're planning a picnic with your friends, you need to know that the weather will be fine so that you can enjoy yourselves.
Many people need to know what the weather will be like so that they can plan their work or other outdoor activities.
Scientists who study the weather are called meteorologists. 
They use many different instruments to collect information about temperature, air pressure, wind speed and direction. They also study the amount of moisture in the air.
Meteorologists measure the speed of the wind with an anemometer, and the amount of moisture with a hygrometer. 
These instruments are used in weather stations on the ground, or in aircraft, ships and weather balloons. Meteorologists use the information from these instruments to forecast what the weather is going to be like.

You will need:
  • a pencil a ruler
  • a piece of thin  card board,
  • 6 inches x 1.5 inches
  • (15 centimeters x 4 centimeters)
  • a piece of stiff cardboard,
  • 8.5 inches x 11 inches
  • (21 centimeters x 27.5 centimeters)
  • a pair of scissors
  • tape
  • a strand of hair, about
  • 8 inches (20 centimeters) long
  • apiece of wood,
  • 11 inches x 2 inches x 2 inches
  • (27.5 centimeters x 5 centimeters x 5 centimeters)
  • six thumb tacks
  • a colored pen with a fine point

You can make your own hygrometer.
Keep a chart of your results every day for three weeks.
Can you forecast whether it will be wet or dry during the fourth week?
1. Using the ruler, draw an arrow about 5 inches by 1 inch (12.5 centimeters x 2.5 centimeters) on the thin cardboard. Cut out the arrow.

2. Tape one end of the strand of hair to the center-top of the stiff cardboard.  

3. Using thumb tacks, attach the stiff cardboard to the long edge of the piece of wood.

4. Attach the free end of the hair to the middle of the back of the arrow.

5. Place the arrow against the cardboard and move it until the hair is stretched out fully and also parallel to the long side of the cardboard. Then attach the end of the arrow (opposite the arrowhead) to the cardboard with a thumb tack.
6. Stand the hygrometer outside. Make sure that it can't fall over. When the sun is shining, mark on the cardboard where the arrow is pointing. Write "dry" by the side of this mark. When the weather is damp, the arrow will point lower. Mark its new position and write "damp" on the cardboard.

How does your hygrometer work?

On a damp day, the strand of hair will absorb moisture from the air. This will make the hair stretch and so the arrow points lower. On dry, sunny days the hair dries out and becomes shorter.

What is the weather?

What is your weather like today? Is it sunny, cold, wet or dry? What causes these different kinds of weather? Heat and light from the sun travel through the earth's atmosphere. The sun's rays affect the air in four ways. They can change its temperature, or the amount of heat it contains. They can change its humidity, or the amount of water it contains. They can change the air pressure, or the force of the atmosphere pushing on the earth. And they can change the wind, or the way the air moves.


Most of the heat given off by the sun is lost in space. Then about one-third of the sunlight that does reach the atmosphere is reflected back into space by the clouds. Less than half the sunlight that gets to the earth's atmosphere actually reaches the planet's surface. This sunlight warms the ground, oceans and lakes, which then reflect warmth back into the air.


Humidity is the amount of water vapor in the air. When sunlight warms oceans, lakes and rivers, some of the water turns into water vapor. The vapor rises into the air, condenses, and forms tiny drops of water that float in the air as clouds. These drops fall to earth as precipitation. That's what scientists call rain, snow, hail or sleet.

Air pressure

What difference does the weight of the air make? Warm air weighs less than cool air, which is why hot-air balloons stay up in the sky. Lighter weights put less pressure on whatever is underneath them. So where there is warmer air, the air pressure is lower. Cool air weighs more, so where the air is cooler, the air pressure is higher.


What is the wind? The wind is air moving from one place to another. Air always moves from where the pressure is high to where the pressure is low. The greater the difference between the levels of high pressure and low pressure, the stronger the wind movement.
Which way does the north wind blow? It blows from the north towards the south. Winds are always named after the direction from which they blow.

How do Rocks Change?

How do Rocks Change?

Have you ever seen waves pounding against the coastline?
The force of the water moves the sand and pebbles on the beach.
Sea and river water are always moving sand, soil and rocks from one place to another.
This process is called erosion. 
Wind and ice also wear away, or erode, rocks and soil. Over thousands of years, erosion can move mountains, dig out or fill in valleys, and change the direction of rivers.

How are rocks broken down?

Rocks feel hard and solid. But they can be broken down.
For example, water which seeps into cracks in rocks may freeze and expand into ice.
The ice splits the rock and breaks it into smaller pieces.
These pieces may be washed away by seas and rivers, blown away by the wind, or moved down a mountainside by a frozen river of ice called a glacier.

How are canyons formed?

Over millions of years, loose stones carried along by large, fast-flowing rivers can erode a passage through solid rock.
The huge valleys they make are called canyons. 
In Arizona, the Colorado River has carved out a deep canyon called the Grand Canyon.
Chemicals in water can dissolve some rocks, leaving behind large caves.
Rain water often mixes with carbon dioxide gas, making a weak acid that eats away some types of rock.
Have you ever seen an archway of rock jutting out into the sea? 
The moving water has worn a hole through the weaker middle parts of this rock.
You might see a rock arch inland, too.

What are sedimentary rocks?

Strong winds blow sand against the rock, wearing away the weaker parts but leaving the firm parts still standing.
Small pieces of rock that are washed or blown away are called sediment.
The sediment will settle somewhere else in layers.
Eventually, these layers are pressed together to make new rocks, called sedimentary rocks.
Flowing river water washes sand, clay and soil down towards the sea.
In some places, where a river meets the sea, this sediment piles up in layers that form a piece of new land called a delta.

In the Arches National Park in Utah, the center of this rock has been worn away to form a large, arched opening.

What are tides and what causes tides?

The waters of an ocean are moving all the time. The surface of the water moves up and down as waves travel across the surface. The level of the ocean rises and falls with the tides. What makes these movements that we call waves and tides? Waves are caused by winds, earthquakes, and the gravitational pull of sun and moon. Waves move forwards, but under each wave, the water moves around in a circle. As each wave reaches the shore, it causes the water near the shore to break into surf.

Water on the surface of an ocean moves up and down while the waves travel along its surface. The water does not really move forward until the wave reaches the shore.
Have you ever gone to a beach along the seacoast to walk or play, but found it completely covered by water? Sometimes, you have to wait as long as six hours before the seashore is uncovered again! These changes in the level of water are called tides. High tide is when the water covers the shore. Low tide is when the beach is uncovered again. High tide and low tide each occur twice at all places on the ocean every day.
Tides happen because of a force called gravity. The gravity of the moon pulls the earth's waters towards the moon. And the gravity of the sun pulls the earth's waters towards the sun.
The moon takes about one month to move around the earth. When the moon is either new or full, the sun, moon and earth lie in a straight line. The tides that happen then are called spring tides, occurring about twice each month. During spring tides, the difference between the level of water at high tide and at low tide is very large. When the sun, moon and earth are at right angles to each other, the tides are called neap tides, also occurring about twice each month. This is when the difference between high tide and low tide is small.
The difference between the level of water at high tide and low tide also varies with the shape of the coast. On the coasts of the Mediterranean Sea, the difference may be as little as 1 foot (30 centimeters). In the Bay of Fundy in eastern Canada, the difference may be as much as 40 feet (12 meters).

Oceans of the earth - What lies under them?

Nearly three-quarters of the earth's surface is covered by water.
The land under the oceans is made up of mountains, valleys and large, flat plains, just like the land on the continents.
It even has volcanoes!

Where did the oceans come from? 

Some scientists believe that the oceans were formed about 4 billion years ago.
At this time, hot rocks inside the earth cooled down and water vapor in the air fell as rain.
The rain gradually filled the low places in the earth's crust and formed the first oceans.

How do we know what lies at the bottom of the ocean? 

Scientists who study the ocean are called oceanographers.
With the help of very accurate instruments, they have made maps of the ocean floor.
Modern oceanographers use a device called an echo sounder to measure the depth of an ocean.
An echo sounder sends down sound waves to the ocean floor, and measures how long it takes for them to echo back to the surface of the water.

What are the Different Types of Rocks?

Take a close look at a small rock. Can you tiny pieces of different colors and apes in it? These pieces are called minerals. Most rocks are a mixture of different minerals. For example, granite consists mainly of quartz and two types of feldspar. It may also contain mica and hornblende.
Scientists who study rocks are called geologists. Geologists have classified all the kinds of rock into three main groups, according to how the rock was originally formed. These groups are igneous rock, sedimentary rock and metamorphic rock.

Igneous Rocks

Molten rock that bursts from the mantle under the earth’s crust cools down and becomes solid. This is called igneous rock. We can clearly see crystal shapes in some igneous rocks, such as granite and basalt. Crystals are clear solids made from atoms arranged in an orderly pattern. An atom is one of the basic units of matter.

Sedimentary rocks

Small pieces of rock are washed down into the sea. These pieces settle in layers, or strata. Over millions of years, more and more layers press down on each other and turn the bottom layers into hard, sedimentary rock.
Sometimes, the remains of dead plants and animals turn to stone in the layers of sedimentary rocks. These remains, called fossils, tell us about life on earth long ago when the rocks they were trapped in were formed.

Metamorphic rocks

Both igneous and sedimentary rocks can be changed into a different kind of rock, called metamorphic rock. This process is often caused by intense heat and pressure underground. For example, the sedimentary rock called limestone can be turned into a metamorphic rock, called marble, in this way.

Why do Volcanoes Erupt?

On our planet, there are about 530 active volcanoes, which might erupt at any time.

Some of them lie under the sea. Each year, only about 25 volcanoes erupt.

Some, such as Stromboli in Italy, erupt frequently.

On the image below, look at the edges of the large sections, or plates, in the earth's crust.
The shaded areas show where most earthquakes happen. Most volcanoes also occur near the edges of these plates.


What happens inside the earth?

Underneath its surface, the earth is a mass of hot rocks and metals. In the mantle, the layer under the earth's crust, it is so hot that some rocks have melted and become molten rocks.
As the rocks melt, they produce gases. The mixture of gas and molten rock is called magma. 
Because it is mixed with - bubbles of gas, the molten rock weighs less than the solid rocks around it. The magma rises towards the earth's surface and collects in hollow spaces called chambers. Some magma chambers are only 1.8 miles (3 kilometers) underground.

Near the edges of the sections called tectonic plates, there are weak places called cracks, or fissures. Strong pressure underground forces the magma to carve a tunnel up through these cracks. When the magma bursts out, a volcano erupts. Gases from the magma become part of the earth's atmosphere, and a hot, fiery liquid, called lava, flows over the ground.

If the lava is quite thin, like soup, it spreads out and makes a wide, flat volcano. Mauna Loa, on Hawaii in the Pacific Ocean, is a volcano that was formed like this. When the lava is thick, like syrup, it makes a cone-shaped volcano with steep sides, such as Mount Fuji in Japan.

Sometimes, underground water is heated by very hot rocks to a temperature above the boiling point. The water changes to steam. Then jets of boiling water and steam, called geysers, burst out of the ground. The rocks that boil the water are sometimes heated by magma chambers.

How Earthquakes Happen?

Would you be frightened if the ground started shaking under your feet?

Sudden, violent movements under the earth's surface are called earthquakes. 

Sometimes, the ground shakes so hard that buildings fall, roads and bridges are smashed and electric power lines break.
Look at this map of the world. The thick, black lines show the edges of the huge sections, or tectonic plates, in the earth's crust.
The shaded areas show places where earthquakes are strongest and happen most often. Most earthquakes occur near the edges of the plates.
Some of the earthquake areas, or zones, are on the land, and some are under the sea.

At the edges of the plates, there are cracks, or faults, in the earth's crust. Over many years, the plates slide past each other slowly, but sometimes the rocks get stuck together. Then the intense heat from inside the earth goes on pushing at them until they bend. Eventually, the pressure suddenly jolts them free, sending shock waves through the ground.

Earthquakes under the sea sometimes make giant ocean waves, called tsunamis. These destructive waves can be as high as 100 feet (30 meters), and happen most often in the Pacific Ocean, near Japan.

How we Measure earthquakes?

Scientists measure the strength of an earthquake in two different ways.
Using a measure called the Richter Scale, they measure the amount of energy that an earthquake releases and give it a score from 0 to 9. An earthquake that measures 9 is one billion times stronger than one that measures 1.

The Mercalli Scale measures the amount of damage an earthquake causes, and gives the damage a score from 1 to 12. A score of 1 means no damage, but a score of 12 means the earthquake has destroyed whole buildings.

It's a Fact

Every two or three minutes there’s an earthquake somewhere in the world.
The earth is always shivering! 

How Mountains are Formed?

Can you believe that the top of the world's tallest mountain was once at the bottom of the sea? Scientists discovered this surprising fact when they examined limestone rocks from the top of Mount Everest, which is nearly 6 miles (9 kilometers) above sea-level. Inside these rocks, they found the remains of dead sea creatures.
Limestone is a kind of rock that is formed in layers, very slowly over thousands of years. The skeletons of animals and the remains of plants that get trapped in one of these layers are changed into fossils. Scientists can tell when and where different creatures lived by examining fossils.
How did rocks from the bottom of the sea get to the top of our tallest mountain? More than 60 million years ago, India was pushed up against the continent of Asia. This happened because of movements in the huge plates of the earth's crust. Before this, India and Asia were completely separate.

The mountains of the world have been formed in different ways. The Himalayas to the north of India, and the Alps to the north of Italy, were formed when plates in the earth's crust were pushed together. When rocks buckle up, or fold in this way, we call them fold mountains.
Another type of mountain is formed when movements of the plates inside the earth's crust create weak areas, or faults, in the crust. As the plates press together, the mantle pushes its way upwards and cracks appear. The land between the cracks is forced up in a block-like shape. This type of mountain is called a block mountain. The Sierra Nevada in the western United States and the mountain ranges of East Africa are examples of block mountains.

What is a Tectonic Plate?

Look at a map of the world.
Can you see the shapes of Africa and South America?
Does it look as if they will fit together?
Make a jigsaw puzzle of the two shapes and find out if they do.

Early in the 20th century, a German scientist called Alfred Wegener studied fossils in rocks from Africa and South America. Fossils are imprints or remains of plants or animals usually found in rocks. He found that the fossils on both continents were the remains of the same animals and plants.
He introduced the theory that mountains in different countries might once have been joined together. 
The Cape Mountains in South Africa, for example, could have once been joined to mountains south of Buenos Aires, in Argentina.
Wegener believed that, over millions of years, the continents had gradually moved away from each other.
Continents are still moving today. Scientists call this movement the continental drift.

What are tectonic plates?

Many scientists now believe that the crust of the earth is not formed in one huge piece, but is divided up into large sections, called tectonic plates.
These solid plates are floating on the mantle, the thick layer of solid rock that also contains hot, liquid rocks moving underneath the earth's crust.

What causes tectonic plates to move? 

It's so hot inside the earth, that some of the molten rocks in the mantle are pushed upwards.
These rocks break through the crust at the weakest points of the crust, usually where two plates meet.
Then the plates are pushed apart.
In other places, cooler rocks in the mantle are pushed downwards towards the hot inner core.
When the plates that make up the earth's crust are pushed together, one plate is forced below the other and melts in the mantle.

How fast are the tectonic plates moving?

Tectonic plates move from less than one inch (2.5 centimeters) to eight inches (20 centimeters) a year.

The Composition and Structure of the Atmosphere

Several layers of air surround our planet. 
Together, these are known as the atmosphere. 

The layer nearest to the earth's surface is called the troposphere. It is about 6 miles (10 kilometers) thick at the poles and 10 miles (16 kilometers) thick at the equator.
About one-fifth of the troposphere is made up of oxygen. Nearly four-fifths is a gas called nitrogen, and the rest is made up of argon, carbon dioxide, and small amounts of other gases.

The top of the troposphere is called the tropopause. Here, the air does not have enough oxygen for living things to survive.
Above the tropopause lies the stratosphere.
This layer is about 21 miles (35 kilometers) thick. It contains a gas called ozone, which is related to oxygen. The ozone forms a layer which acts as a protective shield around the earth. Light from the sun contains powerful ultraviolet rays which can be harmful to living things. Fortunately, the ozone layer stops most of these rays from reaching the earth.

The layers of the atmosphere are rather like the blankets on a bed. If you lie under a lot of blankets, they feel heavy. The large mass of air in the atmosphere is very heavy and presses down hard on the earth. Scientists call this air pressure.
When you stand on the seashore, you are at sea-level. Here, the most air is pressing down on you.

The farther up you go from the sea, the less dense the air becomes. Its pressure becomes less and less.
In the top layer of the atmosphere, called the ionosphere, there is very little air pressure at all.
About 960 miles (1,600 kilometers) above the earth, the atmosphere fades into the airless emptiness of space.

What is the earth made of ?

How do we know what is inside the earth?
Astronauts have traveled about 228,000 miles (380,000 kilometers) above the earth's surface, but no one has ever been able to go very far beneath it.

The deepest mine that humans have ever dug is less than 2.4 miles (4 kilometers) deep, and the longest drill on an oil rig reaches less than 4.8 miles (8 kilometers).
But the center of our planet lies much deeper, about 4,000 miles (6,400 kilometers) below the surface of the earth!

The outer layer of the earth is called the crust. 
If the earth were an apple, the crust would be its skin.
The crust that lies under the oceans is mostly made of a rock called basalt. It is about 5 miles (8 kilometers) thick. The large areas of the earth's crust which are not covered by oceans are mostly made of a rock called granite. These areas are what we call land. They are the continents and islands of the planet.

The continental crust is usually about 19 miles (32 kilometers) thick. In some places, where there are high mountain ranges, it can be more than 25 miles (40 kilometers) thick. Underneath its crust, the earth is made up of three layers of hot rocks and metals. These layers are called the mantle, the outer core and the inner core.

The layer of rock below the crust is the mantle. This mantle is 1,800 miles (2,900 kilometers) thick. At its deepest point, the mantle has a temperature as high as 7950 °F (4,400 °C)—hot enough to melt iron! Some of the rocks here are so hot that they are liquid, or molten. Under the mantle lies the outer core. This is made of molten rocks. The outer core has a temperature ranging from 7950 °F (4,400 °C) to about 11,000 °F (6,100 °C). It is about 1,400 miles (2,250 kilometers) thick.

The center of the earth is called the inner core. It is about 800 miles (1,300 kilometers) thick. Scientists believe that it is ball-shaped and made of two types of metal, iron and nickel. Here, the temperature is very high—about 12,230 °F (7000 °C) —but the metals are solid. This is because of the enormous weight caused by the other layers pressing down on top of them.

The solubility of Gases in Liquids - Solids Liquids and Gases for Kids

Pour a teaspoonful of salt into a glass of water.
Now stir it and watch the salt slowly disappear from sight.
It is dissolving in the water.
How do you know the salt is still there? 
Try tasting a drop of the water.
Gases also dissolve in liquids. 
There is a great deal of dissolved oxygen in both salt water and fresh water.
Fish take in water and extract the oxygen from it. This is the way they breathe.
Every time you have a carbonated drink, you are drinking gas that has been dissolved in liquid.
This gas is carbon dioxide.
Pressure is used to make carbon dioxide dissolve.
The carbonated drink is still under pressure when it is canned in a factory.
When you open a can containing a carbonated drink, you release the pressure and thousands of bubbles of carbon dioxide stream to the surface.
As you drink, you can feel some of the bubbles popping on your tongue.
If you shake the can before opening it, you will increase the carbonation in the drink.
Shaking the drink makes more tiny bubbles of gas form.
When the can is opened, the gas in these bubbles expands instantly, making the drink froth and foam.
If you leave the can open, the carbonation will eventually disappear.
Because it is no longer under pressure, the carbon dioxide will escape into the atmosphere.

Try producing bubbles of gas in a liquid for yourself.
You will need:

  • a teaspoon
  • baking powder
  • a glass
  • water

Put half a teaspoonful of baking powder into a glass and add water.
Stir the mixture.
Describe what happens as the baking powder dissolves.
To show that there is air dissolved in water, fill a glass with tap water and leave it for several hours.
What has happened inside the glass?

How bicycle pump works?

When you pump up your bicycle tires or football, you are making use of compressed air.
Inside a bicycle pump is a small device called a valve.
A valve allows a gas or a liquid to pass through it in one direction only.

Attached to the tire is another valve.
When the plunger of the pump is pushed down, the valve attached to the tire opens and air is forced into the tire.
As the plunger is pulled back, the valve on the tire closes so that no air can escape.
At the same time, the valve on the end of the plunger allows more air into the pump.
Next time the plunger is pushed down, this air is forced into the tire.
If you place your thumb over the hole at the end of a bicycle pump and push in the pump handle, you will compress the air inside into a very small space.
It will become more and more difficult to push farther.

How to make rocket balloon?

Blow up a balloon and then let it go. The force of the high-pressure air coming out of the neck makes the balloon rush aimlessly in all directions. This type of force pushing the balloon forwards is called thrust. It is the same force that makes rockets move.
Space rockets and fireworks rockets all use hot gases to produce thrust. A mixture of substances is set on fire so that it burns very rapidly. The force created by this burning is channeled in one direction, and the thrust makes the rocket move off in the opposite direction.

You can stop a balloon from flying recklessly out of control.
You will need:
a balloon
a medium-sized button

Make sure the balloon end with the button is not pointing towards your eyes.
1. Blow up the balloon and hold it by the neck. Do not tie a knot in the end.
2. Slip the button into the balloon's neck so that the neck closes tightly about the button.
3. Let the balloon go. It will zoom off in a fairly direct line. It will take quite a long time for the balloon to empty, because the air inside cannot escape very quickly.

The stretched rubber of the balloon puts pressure on the air inside, but the button openings control the thrust of the rocket.

How do barometers work?

Look out of your window. Is the air moving?
It is probably moving enough to make the branches on the trees sway slightly.
The weight of this air pressing down all around the earth produces air pressure.
If you live high up above sea level, or even if you go up to the top of a tall skyscraper, the air pressure is less. This is because there is less air above you, and therefore less air pressure.
On the surface of the earth, or near it, air always moves from areas of high pressure to areas of low pressure. Temperature has a great effect on air pressure. As warm air rises, it produces an area of low pressure near the ground. As the air pressure changes from place to place, and from day to day, it helps move air across the earth's surface all the time. As cooler air moves down, it leaves behind an area of high pressure.
You can forecast what the weather will be like for the next few hours by measuring the air pressure.
The instrument used to measure changes in air pressure is called a barometer. If you have one at home, it is probably an aneroid barometer. There's a needle behind a glass-covered dial marked "Fine," "Fair" and "Stormy." If you tap the glass lightly in the morning, the needle points to the weather you can expect that day.
Inside the aneroid barometer is a metal box, or chamber, from which almost all the air has been removed. The metal of the chamber is so thin that small changes in the air pressure outside it make the metal bend. This makes the needle turn round and point to a new position on the dial.
A mercury barometer measures the air pressure more accurately. A long, glass tube is filled with mercury, a silvery liquid metal. The tube is sealed at one end, and placed open end down in a small dish of mercury. Some of the mercury stays in the tube. It is held there by the air pressure at the surface of the mercury in the dish. As the air pressure changes, the column of mercury moves up or down. A scale beside the tube shows the pressure measurements.

What is air pressure? - Solids Liquids and Gases for Kids

Look out of your window.
Is the air moving?
It is probably moving enough to make the branches on the trees sway slightly.
The weight of this air pressing down all around the earth produces air pressure.
If you live high up above sea level, or even if you go up to the top of a tall skyscraper, the air pressure is less. This is because there is less air above you, and therefore less air pressure.
On the surface of the earth, or near it, air always moves from areas of high pressure to areas of low pressure. Temperature has a great effect on air pressure.
As warm air rises, it produces an area of low pressure near the ground.
As the air pressure changes from place to place, and from day to day, it helps move air across the earth's surface all the time.
As cooler air moves down, it leaves behind an area of high pressure.

Cool air is heavier than warm air. 
Cool air sinks down from an area of high pressure, while warm air rises from an area of low pressure.

What is an airfoil and How to Make an Airfoil?

What is an airfoil?

When an airfoil moves through the air, it produces lift because the force of the air pushing down on its top surface is less than the force of the air from below.
The uneven pressure causes lift.
Balloons and airships stay up off the ground because the gas inside them is lighter, or less dense, than the air outside.

But airplanes are heavier than air, so how can they stay in the air?

The shape of an airplane's wings gives it upward movement, or lift. If you look at an airplane from the side, you'll see that the upper surface of the wing is curved, and the lower surface is straighter.
This shape of wing is called an airfoil.
When the plane is in flight, the air which passes over the top of the airfoil has to travel faster than the air which passes underneath it.
This makes the air on the top push down on the airfoil less than the air pushing up from underneath. Therefore, the airplane is lifted up and stays in the air.

Take-off and landing

When an airplane is taking off, it needs a great deal of lift.
If you look at a large airliner, you can see some movable flaps, or ailerons, at the rear, or trailing, edge of the wings.
These ailerons can be lowered.
The lowered flaps increase the top surface of the wing.
This makes air travel even farther over the top surface than over the bottom.
This increases the lift force during take-off. During flight, the ailerons are usually in a normal position, neither up nor down.
But when the aircraft is landing, the flaps are lowered again. Besides maintaining lift with reducing speeds, the lowered ailerons help to slow the plane down.

At take-off, the ailerons on the plane's wings are lowered to provide additional lift. Once the plane is up in the air, the ailerons fit neatly against the wings.

How to Make an Airfoil?

1. Fold the paper in half. Move the edge of the upper half of paper back a little from the edge of the lower half. It will bow upwards.
Carefully stick the edge down with adhesive tape.
2. You have made an airfoil.
Put your airfoil on the edge of a table.
Now place your mouth level with the edge of the table, and blow.
What happens?

How to Make a Pinwheel? - Projects for kids

How to Make a Pinwheel?

You will need:
  1. a pencil a ruler
  2. a piece of thin cardboard, 4 in x 4 in (10 cm x 10 cm)
  3. a pin
  4. scissors
  5. a small bead
  6. a stick, about 10 in long (25 cm)

1. Draw two pencil lines, one from each corner of the card to the opposite corner. Make one small pinhole in each corner, just beside the line, and one hole in the center where the lines cross.

2. Cut along each pencil line toward the center. Cut halfway along each line.

3. Bend over each corner so that all four corner holes are on top of the center hole. Push the pin through the holes.

4. Thread the bead onto the pin behind the pinwheel. Push the point of the pin firmly into the stick.

5. Now blow on your pinwheel.
Which way does it turn?
Does it work better if you blow from the front or from the side?

What is the Atmosphere? - layers of the atmosphere for kids

Do you realize that we live at the bottom of an ocean of gas? 
This ocean of gas is called the atmosphere. 
It is about 100 miles (160 kilometers) deep.
We can best survive in the lower layers of the atmosphere at or near the earth's surface.
This is because there is less and less air to breathe the farther you travel away from the earth's surface.
The earth is wrapped in layers of gases. 
If you could travel high up into the atmosphere, you would travel through these layers or bands of different gases.

What is the ozone layer?

The atmosphere becomes thinner as its altitude (height) above the earth increases.
In the troposphere are all the gases needed by living things on earth.
In the next layer, the stratosphere, is found the ozone layer.
Ozone is a gas formed when ultraviolet rays from the sun change some of the oxygen in the atmosphere to ozone.
Ozone makes a thin layer around the earth and blocks most of the sun's harmful ultraviolet rays, preventing them from reaching the earth.
Some people think ozone smells like garlic.
Others say it smells like seaweed.
Oxygen has no smell at all.
The temperature in the lower stratosphere is only about —67 °F (-55°C).   

Beyond the stratosphere

The stratosphere is about 20 miles (32 kilometers) thick.
The temperature rises steadily as you pass through the stratosphere.
But at the top, the temperature is still only 28 °F (-2°C).
Above the stratosphere lies the mesosphere, and then the ionosphere.
In this band of gases, the temperature becomes very hot.
Radio messages can be sent over long distances by bouncing them off the ionosphere.
The heavier gases like nitrogen tend to stay close to the earth.
So above 60 miles (100 kilometers), you would find more of the lighter gases such as helium and hydrogen.
If you traveled more then 250 miles (400 kilometers) up, you would find so little air that satellites orbiting the earth in this region encounter almost no air resistance.
The temperature is extremely hot—as much as 3600 °F (2000 °C).
In the uppermost part of the atmosphere, the exosphere, the earth's atmosphere gradually merges into outer space.

Composition of Air for Kids - What is Air Made of?

What is the Composition of Air?

Composition of Air About one-fifth of the air is oxygen.   
Human beings and other animals would not be able to survive without oxygen.
When we breathe, our lungs take the oxygen we need from the air.

Another very important gas in the air is carbon dioxide.
When we breathe out, we release carbon dioxide into the air. 
In daylight, plants take in the carbon dioxide they need to live and grow, and they make oxygen.
They then release the oxygen back into the air.
About four-fifths of the air is nitrogen. 
We breathe in nitrogen, but we don't use it.
There are also small amounts of other gases in the air.
Argon is one of these.
We breathe in argon but, like nitrogen, we don't use it.
The air also contains tiny amounts of water vapor.
Green plants take in carbon dioxide from the air. Plants use carbon dioxide and water to make glucose, a type of sugar used for food energy.
Green plants take in carbon dioxide from the air. Plants use carbon dioxide and water to make glucose, a type of sugar used for food energy. In the process, plants give out oxygen through their leaves.

It isn't just living things that use the oxygen in the air. A flame needs oxygen to burn. There's no oxygen in outer space, so you can't light a match there.
Oxygen mixes with other substances too, and it sometimes changes them. Oxygen and water make iron turn to rust. As the iron rusts, it uses up oxygen in the air.
Rusting process experiment

Can we see air?

If you go out on a windy day, you can feel the wind tugging at your body, hair, and clothes.
You can see the trees and flowers bending and the clouds racing across the sky.
Perhaps an old newspaper is blown along the road, or the smoke from a chimney is blowing out sideways instead of going straight up.
What is doing all this pushing and shoving?
What is moving everything about?
It is air.
Can we see air - experiment

Solids liquids and gases for kids - What are gases?-

Have you ever wondered what everything in the world is made from? 
The answer is matter.
Matter is anything that takes up space and has mass.
There are millions of different things in the world, but there are just three different forms of matter.
These are
  • solids, 
  • liquids, and 
  • gases. 
Everything in the world belongs to one of these three main forms.
You can probably think of hundreds of different solids and liquids.
Solids like stone and wood are hard and stay the same shape. Liquids like water and gasoline can flow from place to place.
But gases are different.

How do we use gases?

Did you know that the air around you is a mixture of gases? 
Like most gases, those in the air cannot be seen or smelled, and it is very difficult to make them stay in one place.
You can place a solid or a liquid in a cup or bowl, and it will stay there.
But gases must be kept in closed containers or they will escape.
There are many different kinds of gas.
Some are very useful.
Oxygen is an important gas. It is found in the air. It helps humans and animals to stay alive, and fires to burn.
Some gases come from under the ground. 
They are used as fuels and are burned for heating and cooking.
One kind of gas helps balloons to float up in the air.
Other gases help divers to breathe deep down in the sea.
Gases are also used in factories to make other useful substances such as plastics, bleach, and medicines. They are used in the manufacture of fertilizers, explosives, and dyes.

What is Radioactivity?

The world is changing around us all the time.
There are physical changes as matter changes from solid to liquid to gas.
When water evaporates, the water molecules stay the same but move farther apart.
There are chemical changes, too, such as iron rusting.
When iron atoms combine with oxygen atoms and water, they react together to become a different substance.
There is another way in which matter changes.
Matter can go through a nuclear change.
When a nuclear change happens, the nucleus of the atom sends out invisible rays.
Substances that contain this type of atom are called radioactive substances.
Matter contains some radioactive atoms.
They can be both harmful and useful.
Radioactive atoms have large amounts of energy, which is given out as rays.

How strong is radioactivity?

There are three main kinds of radioactive rays. 

  • A beam of alpha particles is not strong enough to pass through two pieces of strong paper. 
  • A beam of beta particles can pass through paper but can be blocked by a thin sheet of aluminum. 
  • Gamma rays can pass through a concrete wall, Only a thick layer of lead can stop the path of a gamma ray.

Using radioactivity

A gamma ray can be used to check metal pipes and machine parts for cracks. A photograph is taken as the ray passes through the metal.
A beam of beta particles can be used to check if packages are full or empty. If the package is empty, the beam will pass all the way through it.
Materials contain small amounts of radioactive atoms.
In time, these atoms gradually change into different kinds of substances and the radioactivity decays. Scientists can measure the age of rocks and fossils, bones, and even ancient cloth by measuring the amount of radioactivity left in the material.
This is called radiocarbon dating.
Although radioactivity can be very useful, it can also be very dangerous.
If people are exposed to too much radiation, they become ill or die. So radioactive substances must be handled very carefully. People who work in nuclear power stations wear special clothes to protect them from the radiation.

What are Tires Made out of?

What are Tires Made out of?

Think of all the different things that can be made from rubber.
There are gloves, rubber bands, boots and shoes, fan belts for cars, inflatable boats, bottle stoppers, balls, tires, and foam mattresses.
The rubber used to make each of these items is different.
Some rubber is light and spongy, some stretchy, and some hard and stiff. Imagine a mattress made from the rubber in a bottle stopper.
It would be very uncomfortable.
Natural rubber is made from a white liquid called latex. It is the sap which comes from rubber trees.
A V shape is cut in the bark of the tree. The sticky, white latex oozes from the cut and is collected in small cups tied to the tree trunk.
Latex is made of long chains of carbon and hydrogen atoms joined together.
These are called hydrocarbons.
The long hydrocarbons can easily slide past each other while latex is a liquid.
To make latex into a useful, springy solid, it is heated with a substance called sulfur.
The sulfur atoms make bridges between the hydrocarbons and lock them together.
This type of rubber, called vulcanized rubber, is very tough. It is used to make tires.
Scientists are able to take hydrocarbons, and many other basic building blocks of matter, and rearrange them to make new materials.
By changing the pattern of the atoms in natural materials, scientists can make artificial materials.
They can make materials stronger, stiffer, softer, or more elastic.

How are Plastics Made?

Have a look around you.
How many things can you see made from plastics?
In the modern world, different kinds of plastics are everywhere.
Some people even have pieces of plastic in their bodies, such as valves fitted to their hearts, or joints in knees and hips.
Most plastics are synthetic, which means they are not natural, but have been invented by scientists.
Polyvinyl chloride, or PVC for short, is used to make toys, pipes, and raincoats.
Another type of plastic, polytetrafluoroethylene, PTFE, is used to coat the inside of nonstick saucepans. Many pens are made from a plastic called polystyrene.

How is plastic made from oil?

Most plastics are made from chemicals taken from crude oil.
In an oil refinery, oil is separated into several different substances.
One of them is a hydrocarbon called ethylene. 
The molecules of a hydrocarbon combine into long chains called polymers. 
A special chemical called a catalyst is needed to make this happen.
When scientists combine ethylene molecules, they make a polymer called polyethylene. 
Polyethylene is a plastic which is used to make bottles and containers.
By adding different catalysts to different hydrocarbons, other kinds of plastics can be made.

How is Crude Oil Refined?

At the refinery, thousands of tons of oil are turned into useful substances every day.

What is Crude Oil?

Crude oil is a mixture of many different chemicals called hydrocarbons. 
Hydrocarbons are useful because they can be used to make many different substances, such as butane gas, gasoline and diesel fuel, plastics, medicines, and paints.

Crude oil refining process

Before it can be used, crude oil has to be refined.
In the refinery, the crude oil is heated and turned into a mixture of gases and liquids.
The mixture is then passed into a huge fractionating column. 
Inside the column, there are trays at different levels.
The column is hotter at the bottom and cooler at the top.
The gases pass up the column and condense into liquids on the trays at different temperatures.
The gases that have longer molecules, with more carbon atoms, condense at higher temperatures.
Those with shorter molecules and fewer carbon atoms condense at lower temperatures.
This process is another example of fractional distillation.

Different hydrocarbons have different numbers of carbon atoms.

Hydrocarbons with 1 to 5 carbon atoms remain as gas at the top of the column. The gas is used as bottled fuel.
Gasoline has 5 to 10 carbon atoms and is used as fuel for cars.
Naphtha has 8 to 12 carbon atoms and is used to make chemicals.
Kerosene has 9 to 16 carbon atoms and is used as jet fuel.
Diesel oil has 15 to 25 carbon atoms and is used as fuel for trains and ships.
Bitumen has over 20 carbon atoms and is used for sealing roofs.

Separation of Air - How is Air Separated?

Air is a mixture of many different gases. 
These different gases are very useful.
But they must be separated from each other before we can use them.

Air separation process

Air is first changed from a gas to a liquid.
It is compressed, which means it is squeezed into a smaller space, and then cooled to about - 310 °F (-190 °C).
Then the liquid air passes into a tower called a fractionating column. 
The tower is warmer at the bottom and cooler at the top.
The liquid begins to evaporate, turning into gas.
Some gases evaporate at a lower temperature.
Helium and neon collect at the top of the tower.
Nitrogen evaporates next, leaving liquid oxygen at the bottom of the tower.
Separating gases in this way is called fractional distillation.

Gases from the air are used in many different ways.
People with breathing problems cannot take in enough oxygen. They are given special air with extra oxygen added to it.
Fuels cannot burn without oxygen.
A gas called acetylene burns in pure oxygen to give a very hot flame. The flame can melt metals and cut through them.
In sewage plants, oxygen is used to help change harmful substances into harmless ones.
Liquid nitrogen is very cold and is used to freeze foods quickly. It can also freeze liquids in damaged pipes so that the pipes can be repaired.
Substances do not burn in nitrogen, so it is also used inside light bulbs to keep the filament from burning away. In oil tankers, it can prevent fires and explosions.
Plants need nitrogen, so many farmers put fertilizers containing nitrogen compounds into the soil.

Electroplating - What is Electroplating?

What is Electroplating?

If you pass electricity through a solution, you can cause a chemical reaction. 
New substances are produced where the electric current enters and leaves the solution—at the electrodes. Electricity can also change the electrodes themselves.
Here is an experiment you can try.

The method of making a metal coating by means of electricity is called electroplating. 

It is often used to put very thin coats of expensive metals, like silver or gold, onto cheaper metals.
Most gold watches are really made from a mixture of other metals with just a thin electroplating of gold on the surface. 

What does EPNS mean?

Some knives, forks, and spoons are stamped with the letters EPNS.
This stands for Electroplated Nickel Silver. 
The silver coating gives them a bright, shiny surface.
Sometimes metals are coated for protection.
Many machines are made from iron and steel, but these metals rust in damp air.
Chromium metal is tougher but very expensive.
So small amounts of chromium are used to electroplate the surfaces of these cheaper metals.
This makes them look better and last much longer.

Does Salt Water Conduct Electricity?

Electricity flows easily through metal wires.
Copper, aluminum, and silver are good conductors of electricity.
Electricity can also flow easily through some salt, acid, or alkaline solutions.
When electricity flows through a solution, the solution is changed by the flow of electricity, and new substances are produced.

Salt is one of the most important substances in industry. 
  • When an electric current is passed through a salt solution, three very useful substances are produced: chlorine, 
  • hydrogen, and 
  • sodium hydroxide. 
These three substances are so important that millions of tons of salty water are broken down each year using electricity.
Deep under the ground in some parts of the world are enormous layers of solid salt.
One method for removing the salt is to drill holes down to these layers.
Water is then pumped down some holes, and salt solution comes up through others.
This solution contains far more dissolved salt than seawater.
Electricity is passed through the salty water in special tanks to produce the chlorine, hydrogen, and sodium hydroxide. 
Chlorine can be combined with hydrogen to produce hydrochloric acid.
Chlorine and sodium hydroxide also react together, producing a chemical compound called sodium hypochlorite.
So a total of five new substances can be made.

How Metals are Melted?

Knives, forks, ships, trucks, and even bridges can be made from different types of steel. Steel is very strong and is one of the most useful materials in the world. Millions of tons of steel are produced each year.
Steel contains iron mixed with other metals and an element called carbon. Mixtures like this which contain mostly metal are called alloys. Like most other metals, iron is found in rocks. Rocks which contain iron are called iron ore. A part of iron ore is just useless rock, but the rest is iron or a compound called iron oxide. This compound is made up of molecules of iron arid oxygen. Before it can be used to make steel, the iron must be separated from the rock and the oxygen. This is usually done by a special heating method called smelting. Sometimes a process called direct reduction is used.

The smelting is done in a huge blast furnace. A large blast furnace can produce about 3,000 tons of iron in 24 hours

What happens in smelting?

Iron ore is mixed with limestone and coke. The mixture is tipped into the top of a blast furnace. A blast of hot air is blown into the bottom of the furnace. The coke, which is made from coal, burns easily and soon becomes very hot. A gas called carbon monoxide results. The carbon monoxide takes oxygen from the iron oxide. This reaction makes iron and another gas called carbon dioxide.
The iron then melts in the strong heat and trickles down to the bottom of the furnace. At the same time, the rock in the iron ore reacts with the heated limestone to make another liquid mixture called slag. This pours out separately and is sometimes used to make cement. The liquid iron is taken away to be cleaned and mixed with other liquid metals. The resulting mixture then hardens into steel.

What is Melting and Freezing?

Our world is made of matter.
The earth's crust is solid, the sea is liquid, and the air is a mixture of gases. Some matter, such as rocks and wood, are called solids.
They don't change their shape.
Lemonade and water are called liquids because they flow easily. If you pour a liquid into a container, it flows to fill up the shape of the container. The surface of the liquid is always level.
Gases, like the air we breathe, spread to fill any space.
Substances remain as solids, liquids, or gases at certain temperatures. If they are heated or cooled, they change.
If you pour water into a container and leave it in the freezer of a refrigerator, the liquid water changes into a solid, ice. If you heat water until it boils, the liquid water becomes a gas.
If you put some liquid water into the freezer, it soon turns into ice. When you take the ice out of the freezer, it melts back to liquid water again. Ice is solid water.
Freezing water to make ice does not change the water into a different substance — it just changes the form of the water.
Water changes to ice when the temperature falls below 32 °F (0 °C).
Ice melts when the temperature rises above 32 °F (0 °C).
This temperature is called the freezing point of water and the melting point of ice.

What are Acids and Alkalis?

Which drink do you prefer— lemonade or sweet tea?
One is a weak acid and the other a weak alkali.
If not for some sweetener, the lemonade would be a sour-tasting acid, and the tea a bitter-tasting alkali. Any substance that can be dissolved in water is either acidic or alkaline or, if neither, then neutral.
There are many different sorts of acids. 
Carbonated lemonade contains carbonic acid, and the hydrochloric acid in your stomach helps to digest your food.
Car batteries are filled with sulfuric acid. Although these are all acids, they are not all the same strength. Carbonic acid is very weak and sulfuric acid is very strong. If you fill a car battery with lemonade, it certainly won't make enough electricity to start the engine!

There are also strong and weak alkalis.

Bicarbonate of soda (baking soda) is a weak alkali used in cooking.
Sodium hydroxide is a strong alkali that can clean baked-on grease from inside ovens. Scientists use an indicator to test the strength of an acid or an alkali. They add the indicator to a few drops of the substance they want to test. The color of the indicator changes. The color is checked against a color chart.
This shows pH numbers between 1 and 14.

What is pH value?

A pH (potential of hydrogen) number indicates the concentration of hydrogen ions in a solution.
Strong acids are pH 1.
They become weaker as the number rises to pH 6.
Neutral substances are pH 7—neither acidic nor alkaline.
Weak alkalis are pH8. They become stronger as the number rises to pH 14.

Balancing acids with alkalis

When you add an acid to an alkali, the alkaline substance and the acid balance each other out. Scientists say they neutralize each other. People can get indigestion pains when there is too much acid in their stomachs. Look at a packet of indigestion tablets. You'll see they contain bicarbonate of soda, also called baking soda or sodium bicarbonate.
Whydo you think this helps?