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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? 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, o...

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 ...

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 eq...

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 stif...

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. Temperature 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 Humidity is the amount of water vapor in the air. When sunlight warms oceans, lakes and ...

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 mak...

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....

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.

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 m...

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...

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...

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 ...

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 ea...

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. ...

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 plac...

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 d...

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.

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 lon...

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 i...

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? 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 Wh...

How to Make a Pinwheel? You will need: a pencil a ruler a piece of thin cardboard, 4 in x 4 in (10 cm x 10 cm) a pin scissors a small bead 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?

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, preventi...

What is the 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.  In the process, plants give out oxygen ...

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. S...

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 thro...

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 ...

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 ...

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...