My Science School

Kinetic energy largely dominates the beautiful game of football as players cover a number of kilometres in a 90-minute game, in search of goals that separate the competing sides. But one of the more dramatic moments produced on the football field depends mainly on the potential energy of a player.

Energy and forces

The overhead kick, also known as the bicycle kick and scissors kick based on minor differences, sees the player utilising potential energy to carry out the acrobatic move. There are also forces in action as a player needs to contend with centrifugal and gravitational forces while trying to kick the ball overhead.

Three main phases

The overhead kick can be broadly broken down into three phases. The first, and most obvious phase, is the jump. The player places himself such that their centre of gravity is a little behind their impulse foot. This enables the player to gain rotational momentum by applying pressure on the ground. The jump phase is thus similar to the back somersault.

There is very little separating the second and third phase as it all happens really quickly in reality. The second phase is the kicking movement done by the player once completely air-borne. With other forces in action, the player needs great strength in their thighs and muscles to carry out this phase.

Changes direction and spread

The third and final phase is the moment of impact, when the player’s foot strikes the ball. When struck properly, the ball not only change direction, but also gains considerable velocity.

While all these happen within seconds, what really matters for the player is what happens next. What we have just described might seem like poetry in motion for those who love physics, but for footballers, their goal with these kind of shots is to find the ball in the back of the net!

 

Picture Credit : Google

Kinetic energy largely dominates the beautiful game of football as players cover a number of kilometres in a 90-minute game, in search of goals that separate the competing sides. But one of the more dramatic moments produced on the football field depends mainly on the potential energy of a player.

Energy and forces

The overhead kick, also known as the bicycle kick and scissors kick based on minor differences, sees the player utilising potential energy to carry out the acrobatic move. There are also forces in action as a player needs to contend with centrifugal and gravitational forces while trying to kick the ball overhead.

Three main phases

The overhead kick can be broadly broken down into three phases. The first, and most obvious phase, is the jump. The player places himself such that their centre of gravity is a little behind their impulse foot. This enables the player to gain rotational momentum by applying pressure on the ground. The jump phase is thus similar to the back somersault.

There is very little separating the second and third phase as it all happens really quickly in reality. The second phase is the kicking movement done by the player once completely air-borne. With other forces in action, the player needs great strength in their thighs and muscles to carry out this phase.

Changes direction and spread

The third and final phase is the moment of impact, when the player’s foot strikes the ball. When struck properly, the ball not only change direction, but also gains considerable velocity.

While all these happen within seconds, what really matters for the player is what happens next. What we have just described might seem like poetry in motion for those who love physics, but for footballers, their goal with these kind of shots is to find the ball in the back of the net!

 

Picture Credit : Google

The World’s Ocean

Do you think the earth’s surface has more land or more water? Would you believe that most of the planet is covered with water? It’s true. The land we live on, even the giant continents, are really just like big islands in a huge ocean.

Different parts of the ocean have different names, although all these parts combine to form one giant body of water. The two biggest parts are the Pacific and Atlantic oceans. There are also the Indian and Arctic oceans. Some people call the water near the South Pole the Antarctic Ocean. Can you find these parts of the world’s ocean on the globe?

Where did the ocean come from? Many scientists say that billions of years ago the outside of the earth was cool, but the inside was fiercely hot. The heat inside the earth caused chemicals to rise to the surface. Some of these chemicals formed water. Over millions of years, the water filled the low parts of the earth.

On a quiet day, you can hear the waves roll in and splash near the shore. On a stormy day, they thunder.

Waves are made by wind blowing along the top of the water. The water seems to be moving forwards - but it only moves up and down. A cork floating on the water would bob up and down as a wave moved under it. This is because the water in a wave does not move forwards. Only the shape of the wave moves forwards.

When a wave reaches land, it “breaks”. The bottom of the wave drags on the ground where the water is shallow. The top keeps going. It spills onto the beach, and then slides back again. This is the only place where the water in a wave moves forwards and back. Everywhere else it just moves up and down.

The biggest waves of all are made by earthquakes under the ocean floor. These waves are called tsunamis. Hundreds of kilometres from shore, a tsunami may only reach 30 or 60 centimetres. People on a ship at sea may not even feel it. But as a tsunami approaches land, it can form a wall of water more than 30 metres high.

All that ice

A glacier is a large mass of ice that flows slowly over land in cold Polar Regions and high mountain valleys. Glaciers begin as snow on a mountaintop. As more snow falls, the weight of the new snow squeezes the snow already there. The snow on the bottom of the pile turns to ice. The ice becomes a glacier.

There are two kinds or glaciers. One is like a river of ice that slides down from the top of a mountain. The other is like frosting on a cake. It may cover entire mountain ranges and even whole continents.

When a glacier reaches the edge of the frozen land, a large crack will appear in it. With a loud noise like thunder, a huge piece of the glacier falls into the sea and floats away. This piece is called an iceberg.

The land called Antarctica, around the South Pole, is covered by a giant glacier. A sheet of ice that is more than 1.6 kilometres thick covers Antarctica. Under much of this ice is land with mountains, valleys, and plains.

Picture Credit : Google

The Bottom of the Sea

The sea floor has many mountains, plains, deep valleys, and even volcanoes! Its mountain ranges are longer and wider than those on land. Its valleys are longer and deeper, too.

The earth’s surface is covered with a rocky crust. The high parts are the continents and islands, and the low parts are under the sea. The deepest parts are long, narrow valleys called trenches. Earth’s deepest trench is almost 11 kilometres deep in one spot.

Large mountains rise from the sea floor. In some places, they rise high enough to appear above the water. Many of these mountains are volcanoes. Hawaii is made up of volcanic islands.

Great mountain ranges in the oceans are called ridges. Iceland is part of a ridge in the middle of the Atlantic Ocean. Smaller ridges are found in the Pacific Ocean.

Isn’t it surprising that you can find all of these different kinds of land at the bottom of the sea?

Picture Credit : Google

Have you ever travelled across land where the sky seems bigger than the countryside around you? If so you probably saw a part of the earth called a plain. The land is so flat that you can see great distances all around.

Most plains are lower than the land around them, but they are not deep like a valley. Many people live on plains because the soil is good for farming. Also, building homes and roads is easier on the flat land of plains than it is in mountainous places.

Plains may be found along a coast or inland. Coastal plains are lowlands that stretch along an ocean’s shore. They might be elevated parts of the ocean floor. Or they can be formed by solid materials carried off by water from other coastal plains. Coastal plains usually rise from sea level until they meet higher land, such as mountains.

Inland plains may be found at high levels. The Great Plains, which cover part of the U.S.A. and Canada, slope upwards from about 600 to 1,000 metres above sea level. There they meet the Rocky Mountains.

Thick forests thrive in the damp air along coastal plains. Other plains, like those in which the sky seems so big, have few trees, but they have lots of grasses.

If the highest part of the land is a mountaintop, what do you think the lowest place is? That’s right - a valley.

Most valleys begin as land with a stream or river running through it. As the river   flows along, it breaks off pieces of the land and carries them away. This deepens the river’s path and changes the land beside it.

Over time, water cuts deeper into the earth, making steep walls. Wind and rain wear away at the walls, and this makes the valley widen.

The part of the valley where water flows is called the valley floor. As the valley widens, its floor and walls change shape. Valleys that are long and narrow with steep sides are called canyons or gorges. Valleys in low-lying plains can be very spread out. Many valleys become so wide that people live in them.

Most valleys are formed by running water, but some form in other ways. Some valleys form where the ground sinks, like the valley the Dead Sea is in between the countries of Jordan and Israel. It is the lowest dry land on the earth. Other valleys can be found high in the mountains where moving piles of snow and ice called glaciers scrape out deep valleys. There are even valleys on the ocean floor.

The Ground Shakes

The ground shivers, shakes, and rumbles. Whole sections of land move, and even mountains seem to move. What is happening? It’s an earthquake!

What causes earthquakes? Earthquakes start in the earth’s crust. Pressure builds and pushes rocks until they bend. If you bend a stick long enough, it snaps and breaks. The rocks break, too. When this happens, shivers and quakes rush through the ground. Sometimes a deep rumbling sound fills the air. Sometimes whole pieces of land move.

Thousands of earthquakes that are strong enough to be felt occur somewhere on earth each year. Some people live where small earthquakes happen often. Lamps and hanging plants swing a little. Dishes may rattle. Cars may rock.

In very strong earthquakes, the walls in buildings crack. Bridges collapse, power lines break, and fires begin. In a really bad earthquake, the ground may split open.

People who study earthquakes are called seismologists. They measure the movement of a quake and the damage it causes. They also try to judge when a quake will happen so they can warn people who might be in danger.

An Island is born

Day after day, huge explosions filled the air. The ocean sizzled as hot rock and ash shot up from the sea floor. Soon, a large mound of dark, melted rock rose out of the water. Far out in the sea, a new volcano was born.

After it rose above the surface of the ocean, the new volcano was called an island. This island formed in the ocean near the southern coast of Iceland. It is called Surtsey. It is really an underwater volcano, and its bottom lies under the sea.

For four months, huge explosions sent steam and ash into the air. Steam sometimes rose as high as 6 kilometres. Then flaming hot lava began to flow. When it hit the cold water, the lava cooled and hardened, forming a cone-shaped mountain. The volcano erupted for about three and a half years.

Today, Surtsey covers an area of nearly 2.6 square kilometres. From a distance, the island appears to have no life on it. But scientists who visit it are finding insects and spiders there, as well as plants that started from seeds carried by birds, wind, and water.

Picture Credit : Google

A volcano is a special kind of mountain that actually builds itself! It is made of red-hot rock that pushed up out of a crack in the earth.

A volcano begins deep inside the earth when the force of hot gas pushes melted rock up. With a loud, deep rumble, the ground begins to shake and burst open. Fiery hot rock can shoot into the air, and melted rock may flow out of the earth. With the volcano, there may be earthquakes and explosions. Huge clouds of smoke and ash may fill the air.

The melted rock is called magma. Magma that pours out onto the earth’s surface is called lava. Some lava is as thick as syrup, and some is as thin as soup.

As thin lava stops flowing and cools, it hardens into smooth sheets of rock. Thicker lava cools into rough, jagged sheets.

As more lava pours out of the earth, it falls on the cooled rock. As the ash and rock pile up, a new mountain forms. It forms a cone-shaped mountain with a deep tunnel down its middle.

Picture Credit : Google

Some mountains are no more than steep hills covered with grass and trees. Others rise high into the atmosphere with snow-covered peaks. Often mountains stretch out in long chains called mountain ranges.

Mountains are formed over long periods by tremendous forces in the earth. These forces move parts of the earth’s crust in different ways, making different kinds of mountains.

Mountain ranges are important because they influence the climate and water flow of the land around them. How do they do this? Air cools as it reaches high altitudes. And cold air holds less water than warm air does. So as the warm air turns cooler near the tops of the mountains, it releases water in the form of rain or snow. This rain or snow feeds nearby rivers and streams. Mountains are also important as homes for plants and animals and as a source for minerals.

Scientists say the earth’s mountains are millions of years old. The youngest mountains have rugged, sharp peaks. Older mountains are smoother, with rounded tops. These older mountains have been worn down by wind and rain over millions of years.

But all mountains begin to wear away, or erode, even while they are rising. Rainfall washes away tiny pieces of rock. The wind carries away dust and earth.

Water seeps into cracks in the rock and freezes. Ice takes up more space than water, so it forces the cracks open. This happens over and over until rocks break off and fall down the mountainside. After millions and millions of years, all of these forces wear away the mountains.

There are five different kinds of mountains.

Fold Mountains form when sections of the earth’s crust meet head-on. This makes layers of rock in the crust crumple and fold. They often make wave-like patterns.

Fault-block Mountains form when earthquakes make the earth’s crust break into large blocks that are tilted or pushed out of place.

Dome Mountains form when forces inside the earth push the earth’s crust up into a huge bulge or dome.

Erosion Mountains form when rivers or glaciers flow over a high, flat area of rock. They wear it away to form peaks and valleys.

Volcanic Mountains form when molten rock from deep within the earth erupts. It pushes up through the earth and piles up on the surface.

The Earth’s Plates

It may seem that the earth’s crust is one gigantic piece of rock. But the outer shell of the earth is divided into about 30 large and small pieces that fit together like a puzzle. These pieces are called tectonic plates.

The plates move on a very hot layer of rock within the mantle. The plates move very slowly, only from 1.3 to 20 centimetres per year.

The continents sit on top of the plates. When the plates move, they take the continents with them. But the plates aren’t only under the continents. They are also under the ocean floor. They are under water on the continents, such as lakes and rivers, too.

Under land, the plates are about 100 kilometres thick in most places. In some places in the world’s oceans, they may be less than 8 kilometres thick.

As the plates move, the continents and oceans slowly change. Scientists think that in 50 million years, South America and Africa will be further apart. They think the Atlantic Ocean will be wider, and the Pacific Ocean will be smaller.

Picture Credit : Google

Some of the world’s best detectives are the people who study the earth. They are called geologists.

Geologists help us learn about the earth’s resources and how to care for them. They tell us how to preserve these resources and to use them properly when we must. Some geologists study where to build homes, bridges, and dams safely. These scientists also work to protect people from earthquakes, floods, and other natural disasters.

Geologists may be found chipping rocks on a mountainside or drilling on the ocean floor. Sometimes geologists work indoors. They X-ray rock samples, do research and tests on computers, or make maps of places they want to explore.

Geologists may travel all over the world. They search mountains, swamps, deserts, and the bottom of the ocean, so that we can learn more about the earth. They may tramp through rain forests, go underground into mines, or climb around an icy glacier.

Geologists and many other kinds of scientists uncover the secrets of the earth in different ways. Sometimes such scientists are called earth scientists.

Environmental geologists work to solve problems of pollution. They search for the best ways to get rid of hazardous waste - materials that are dangerous to our health.

Meteorologists study the weather and the air that surrounds the earth. They predict weather conditions.

Mining geologists study the earth’s rocks and ways to remove them.

Mineralogists identify and study the 3, 000 or so kinds of minerals found on the earth.

Petroleum geologists search for oil and natural gas on land and beneath the ocean floor.

Seismologists study the motion of the earth. They watch for earthquakes. Most earthquakes occur underwater.

Geochemists study the chemicals in the earth’s crust, its waters, and its atmosphere and why they are there.

Palaeontologists study fossils of animals and plants to learn about the earth’s past.

There are many kinds of earth scientists, but they have one thing in common. They all enjoy studying the earth and want to uncover its secrets.

Picture Credit : Google

Metals are found in earth’s rocks. In order to use the metal, the kind of rock that contains the metal must be mined, or dug out of the ground. This rock that contains the metal is called ore.

Many ores are found beneath the ground in layers of rock called veins. Iron ore is mined. After it is mined, the ore is smelted. Smelting removes metal from the ore. The ore is put into a huge furnace and mixed with other rocks. Hot air is blasted into the furnace. When the furnace is hot enough, the liquid iron sinks to the bottom. It then is poured into a container that holds many tonnes of molten, or melted, iron.

Steel is made by heating iron and mixing it with a small amount of a chemical called carbon. Steel is used to make such things as car parts, buildings, screws, and paper clips.

Aluminium is light, strong, and doesn’t rust. It comes from an ore called bauxite. To make aluminium, the compound called alumina must be removed from the bauxite. Aluminium is used for many things, including pots and pans, aeroplane parts, and chewing gum wrappers.

Gold and silver ores are hard to find and sometimes are found as natural metals. Both are heavy, but very soft. Gold and silver are used in coins and jewellery.

Picture Credit : Google