My Science School

Energy is needed to make things happen. Every movement or change, no matter how small, requires energy. Energy has many different forms. For example, some types of energy are needed to move cars or light up homes. You body needs energy to move, grow, and keep warm.

Movement

All moving things have energy, from dogs to waterfalls. The faster something moves, the more energy it has.

Chemical

There is energy stored inside the chemicals in food. When animals eat, their body breaks down the food, releasing the energy.

Electrical

Electrical energy is used to power things in our homes, such as a television. Electricity flows easily through wires. Lightning is also caused by electrical energy.

Light

Glowing objects give out light energy, which we see with our eyes. Nearly all the energy on Earth comes originally from the Sun.

Sound

Sound is a form of energy that is produced when objects vibrate, or shake. For example, when a bell is hit, it makes a sound. We receive sound energy through our ears. This is called hearing.

Heat

Hot things contain lots of heat energy. They pass on this energy to cooler things around them, so hot things like a fire can be used to keep us warm. We get most of our heat energy from the Sun, and from burning things, such as wood.

Stored energy

Sometimes energy is trapped inside things. This is called stored, or potential, energy. When this stored energy is released, it can make things happen. A stretched catapult stores elastic energy. When you release it, it gives energy to the ball, making the ball fly out. The more the catapult elastic is stretched, the more stored energy it has.

 

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Machines are used to make a task easier. They reduce the amount of effort that we need to put in (the force) to lift or move a heavy object (the load). Machines can also change the direction of a force, so we can move things in a more helpful way.

Lever

A lever is a bar that swivels on a fixed point, called a fulcrum, and makes it easier to lift a heavy load. If you push down at one end of the lever, the load at the other end is raised.

Slope

It is much easier to push or pull something heavy up a slope than it would be to lift it straight up because less force is needed. However, you have to push or pull the object a greater distance to get it to the same place.

Gears

Gears are wheels with teeth that fit together. When one gear is turned, the other one turns in the opposite direction. If the gears are different sizes, they turn at different speeds.

Wedge

A wedge helps us to push things apart. The blade of an axe is a type of wedge. When the axe is swung and the blade hits a piece of wood, the wedge forces the wood to split apart.

Pulley

A pulley makes it easier to lift a heavy object (load) straight up. A rope is looped over a wheel and one end of the rope is attached to the load. It is easier to lift the load by pulling down on the rope than by picking it up.

Wheels and axle

A wheel and axle work as a turning machine that makes it easier to move something from one place to another. When the axle is turned, the rim of the wheel turns more quickly.

Screw

A screw changes a small turning force into a large downwards force. It has a spiral pattern, called a “thread”, which runs round the screw. Each time the screw is turned, the thread pulls it down a bit.

 

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Gravity is an invisible force that pulls things towards the centre of the Earth. It pulls everything towards the Earth, whether the object is in the air, in water, or already on the ground. Even the Moon is kept moving around the Earth by the pull of Earth’s gravity.

Leaping squirrel

Gravity keeps things held to the Earth. For something to be able to lift off the ground, it has to produce a force large enough to overcome the force of gravity.

Jumping up

When the squirrel jumps, its legs push against the branch, producing an upwards force. This force is greater than the force of gravity, so the squirrel lifts off the branch.

Gaining height

There is no longer a force from the legs. The squirrel keeps moving upwards, but the force of gravity slows it down.

Falling down

The squirrel slows down so much that for a tiny moment it stays totally still in the air. Then gravity causes the squirrel to begin to fall towards the ground.

Landed

Once the squirrel landed on another branch, the force of gravity holds it there until it decides to jump again.

The Moon

The Moon has its own gravity, but because it is smaller than the Earth, its force of gravity is not so strong. The squirrel would feel lighter on the Moon, and it would be able to jump almost seven times higher.

Blast off!

A huge explosion is needed to produce enough force to overcome the force of Earth’s gravity and launch a rocket into space.

 

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Friction is a force that slows things down. It occurs when two surfaces rub against each other. Different types of surface produce different amounts of friction. Smooth surfaces, such as ice, do not create much friction, so things slide over them easily. Rough surfaces, such as roads, produce a lot of friction. This helps car wheels to grip the road, and allows cars to stop easily.

Super friction

If the pages of two books are interleaved, it is almost impossible to pull them apart. This is because there are hundreds of pages, and therefore hundreds of surfaces, that are trying to slide against each other at the same time. This produces an enormous amount of friction, which stops the pages being pulled apart.

Sliding race

Four metal bobsleighs are held at the top of a slope. Each slope has a different surface.  Bobsleighs are let go of at the same time.

Slippery surface

A smooth surface, such as this slope covered in oil, creates hardly any friction. Objects slide very easily and quickly along them. Ice skaters and skiers make use of slippery surfaces.

Wooden floorboards

Floorboards are fairly smooth, producing only a little friction, which allows objects to slide over them quite easily. This is why you can sometimes slide on floorboards in your socks.

Scratchy sandpaper

Sandpaper is rough and so creates quite a lot of friction. This means that an object sliding over sandpaper will slow down and stop more quickly than an object sliding over a smoother surface.

Green grass

A very rough surface like grass produce lots of friction, causing an object sliding over it to slow down a lot. The longer the grass, the more quickly the object will slow down.

 

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Nothing can move without a force to start it on its way. Forces are also needed to make things move faster, to change their direction, and to make them stop. In 1687, the English scientist Issac Newton came up with three simple ideas that show how forces affect the way things move. These ideas are called the Laws of Motion.

Newton’s First Law

If an object is not moving, it will stay completely still unless an outside force acts on it. If an object is already moving, it will keep on moving at the same speed, and in a straight line, unless an outside force, such as gravity, causes it to change its motion.

Newton’s Second Law

If an outside force pushes or pulls on an object that is not moving, it will start to move in the same direction as the force. If an object is already moving, an outside force will cause it to move faster, slow down, or change direction.

Newton’s Third Law

This law says that “Every action has an equal and opposite reaction”. This means that when a force acts in one direction, it creates another equal force in the opposite direction. An example of this is a ball bouncing off a wall. For example: the ball will stay where it is until it is kicked, or blown by a strong gust of wind. The kick provides a pushing force on the ball. The ball moves off in the same direction as the force. When this ball hits the wall, it pushes against the wall in the direction it was moving in.

Moving forever

Every object that is moving through air will eventually come to a stop, because the air pushes back against the moving object, slowing it down. This force is called air resistance. However, in space there is no air, which means that once something starts to move, it will keep moving forever! This is an example of Newton’s First Law.

 

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A force is a push or pull. Forces are needed to make things move. They can also make things speed up, slow down, or stop moving. Forces can also cause things to change direction or change shape. Most forces only act when things touch each other. Other forces, such as gravity and magnetism, act at a distance.

Pushing forces

A sail boat uses the pushing force of the wind to start moving and to keep moving in the water. If the wind dies down, the boat will slow down and eventually stop, because the air and water are pushing back against it.

Wind

The wind pushes against the sail, moving the boat forwards through the water.

Air resistance

As the boat moves forwards, the air pushes back against it. This is called air resistance. You can feel the force of air resistance on your face when you pedal hard on a bicycle.

Water resistance

As the boat moves forwards, the water pushes back against it. You can feel the force of water resistance when you try to run through water.

Pulling forces

A small tugboat is able to pull a much larger ship through water because it has a very powerful engine. The engine produces a strong pulling force, which acts through the towline connecting the two boats.

 

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Almost three-quarters of the Earth’s surface is water. Water is found in rivers, lakes and oceans, and it can also be seen as tiny water droplets in clouds, or falling to Earth as rain or snow. Water is constantly moving from one place to another around the planet. This movement is called the water cycle.

Water on the move

The constant cycle of evaporation and condensation of water is almost entirely caused by heat from the Sun. the sun’s rays warm the land and the oceans. Heat from the Sun causes water in the ocean to evaporate, turning into invisible water vapour. Water also evaporates from rivers and lakes. As water vapour rises it cools, and condenses into tiny droplets, forming white clouds. Clouds are blown across the land by the wind. As clouds rise and cool, the tiny droplets come together and fall as rain or snow. Rain runs over the surface of the land and collects in streams and lakes. Snow from the mountains melts and forms streams. Streams join to form large rivers, which flow downhill. Rivers flow into the ocean. Groundwater eventually runs into the ocean. Water sinks into the ground, forming groundwater beneath the surface of the Earth.

Extreme conditions

Deserts are places where very little rain falls. The Atacama Desert in Chile is the driest place in the world, with only 15 mm (0.6 in) of rain every year. The wettest place on Earth is Mawsynram in India, which has 11,872 mm (467 in) of rain every year.

 

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Changes are taking place in the world around us all the time. Sometimes, after a change, things can be put back to the way they were before. Other types of change leave things altered forever.

Reversible change

Reversible changes are easy to reverse, or undo. For example, ice can melt to become water, and then freeze, turning back into ice again. A frozen lolly is solid. It is made of ice. If you take the ice lolly out of the freezer, it gets warm and the ice begins to melt. After a while, all of the ice has melted and has become a liquid. The liquid can be poured into a lolly mould and then put into a freezer. As the liquid gets cold it freezes and turns into ice.

Irreversible change

Irreversible changes cannot be undone. They are permanent. For example, once you have cooked an egg, it cannot be turned back into a raw one! The white of a raw egg is a clear, runny liquid. Heating the egg causes a change that cannot be undone. The egg white has now become a white solid. It cannot be turned back into a clear liquid.

Everyday changes

Here are some examples of common reversible and irreversible changes that you may see from time to time.

Steamed window

When invisible water vapour in the air hits a cold window, it condenses, turning into tiny water droplets. When the window gets warm, the droplets turn back into water vapour.

Autumn leaves

Most trees lose their leaves in autumn. Before the leaves fall off the tree, they charge from green to red to brown. This change cannot be undone, which means it is permanent.

Rusting

Rust forms slowly when iron comes into contact with air and water. Iron objects left in the rain become flaky and reddish-brown forever.

Rotting food

When food gets old, it can be attacked by tiny living things called mould and bacteria. As the food rots it turns brown, smells nasty, and shrivels up. It cannot be changed back into its fresh form again.

 

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Solids, liquids, and gas can sometimes be mixed together. For example, you can have a mixture of two or more solids, or you can mix a solid with a liquid. Sometimes, when a solid mixes with a liquid, the solid disappears. The solid is said to have dissolved, and this type of mixture is called a solution. It is fairly easy to separate any mixture back into the different things that formed it.

Separating mixtures

Mixtures can be separated back into their different parts. Choosing the correct method depends on what type of things the mixture is made up of.

Sieving

Sieving can be used to separate a mixture of solids, but the solids must be different sizes. Liquids containing large solids can also be separated by sieving. For example: a mixture of solids is passed through a sieve. The small bits of solid pass through the holes in the sieve. The sieve stops the big bits of solid from getting through.

Filtering

Mixtures of solids and liquids can be separated by a process called filtration. The mixture is passed through a fine mesh, such as filter paper, which holds back the solid bits, but allows the liquid through. For example: a mixture of a solid and a liquid is passed through filter paper. The liquid passes through the tiny holes in the filter paper. The filter paper stops the solid bits from getting through, even very small pieces of solid, such as grains of sand.

Evaporating

When a solid has dissolved in a liquid to form a solution, it cannot be separated by filtration. The solution must be heated until the liquid evaporates, leaving the solid behind. For example: a solution of sugary water is heated in a pan. The hot water evaporates. Eventually, all the water evaporates and solid sugar is left behind in the pan.

 

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Some materials are found naturally on Earth, others are made by humans. One material may be hard and brittle, while another may be soft and bendy. These types of features are called “properties”. We choose a material for a specific job based on its properties. For example, you wouldn’t build a castle out of chocolate!

Metal

Metals are usually strong, but not brittle, which means they do not break easily. Iron, for example, may be used to make strong chains. Metals are also good at allowing heat and electricity to pass through them.

Types of metal

Different metals have different properties and so are used to make different things.

• Gold is a shiny metal from which crowns and jewellery are made.


• Iron is heavy. Heated flatirons were once used to press clothes.


• Aluminium is a light metal. It is used to make cans and aircraft.


• Copper is easy to bend. It is often used for water pipes or wires.

Brick

Bricks are rectangular blocks of clay mixed with sand. They are heated to a high temperature to make them very hard. Because we can make as many bricks as we want that are exactly the same size, they are an ideal building material.

Glass

Glass is made by melting sand. It is transparent, which means we can see through it. So it is often used to make windows, it can also be made in different colours. Glass is hard, but brittle and so can easily be broken.

Wood

Wood comes from the trunks of trees. It is strong and light. Wood is easy to cut into different shapes, so it is sued to make bridges, buildings, and furniture. Wood is also easy to set on fire. Burning wood is useful because it produces heat.

Cloth

Cloth can be made by knitting or weaving cotton, wool, or silk. It is a soft, light material, and people have made clothes from it for thousands of years. It can also be used to make coloured flags.

Rock

Rock is a natural material. For example, mountains are made of rock. Some rocks are hard, but others are soft and crumbly such as chalk. Humans have often used hard rocks to build tall, strong walls.

 

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Matter is the “stuff” that all things are made of. Everything we see, touch, and breathe is made of matter. Matter has different forms called states. The three most common states on Earth are solids, liquids, and gases. Matter behaves differently in each of these states.

Solid

A solid is something that holds its shape, and stops you from moving through it. For example: a rock, a spoon, or a book.

• Solids can be cut or shaped.


• Most solids are hard, like metal.

Liquid

Liquids do not hold their shape on their own. They will take on the shape of their container, like water in a glass.

• Liquids flow, like river, and they can be poured, like milk and juice.


• Liquids fall down, as they are pulled towards the Earth by gravity.

Gas

Gases have no fixed shape at all. They fill any space that they are in, for example, air in a room.

• Gases are always moving.


• Gases are lighter than solids and liquids.

Switching states

Most things change from one state to another when their temperature changes. When a solid gets hot, it melts and changes into a liquid. When this liquid is heated, it evaporates, changing into a gas or vapour. For example: Ice is a solid. It is very cold. When ice is heated above 0ºC  (32ºF) , it melts and becomes a liquid called water. When water is heated to 100ºC  (212ºF), it boils and changes into a vapour called steam.

 

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Science isn’t just a lot of facts in a book. Science is a way of thinking. Science is about asking questions and finding out the answers. Scientists come up with new ideas, and invent new ways to make life easier for everyone. Here are some examples of things that can be explained by science.

• Where does electricity come from?


• What materials conduct electricity?


• Where does lightning come from?


• Why do plants need sunshine?


• Why do humans have bones?


• How do you know if something is alive?


• How are shadows made?


• Where does light come from?


• Why do only some things stick to magnets?


• What is a magnet?


• What is the hardest material on Earth?


• What is gas?

Bright sparks

Electricity is one of several different types of energy that have been studies by scientists. Electrical energy flows through wires, and is used to power things like lights and computers.

Life on Earth

Cats aren’t the only curious animals that live on Earth! Scientists have already discovered animals, plants, and other living things, and they think that there may be many more.

Material matters

Everything around you is made of matter, and that includes body! Scientists have explained how matter can take different forms, and why it behaves differently when it is a solid, liquid or gas.

Forces of attraction

Magnets produce an invisible pulling and pushing force called magnetism. The Ancient Greeks knew this force existed, but it took until 1279 for a scientist to explain how it works!

Casting shadows

Have you ever wondered why you only sometimes have a shadow, and why its length changes? Well, science has the answer.

 

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Glaucoma is a group of eye conditions that damage the optic nerve, the health of which is vital for good vision. This damage is often caused by an abnormally high pressure in your eye. Many forms of glaucoma have no warning signs. The effect is so gradual that you may not notice a change in vision until the condition is at an advanced stage.

Glaucoma is the result of damage to the optic nerve. As this nerve gradually deteriorates, blind spots develop in your visual field. For reasons that doctors don't fully understand, this nerve damage is usually related to increased pressure in the eye.

Glaucoma tends to run in families. In some people, scientists have identified genes related to high eye pressure and optic nerve damage. Promptly go to an emergency room or an eye doctor's (ophthalmologist's) office if you experience some of the symptoms of acute angle-closure glaucoma, such as severe headache, eye pain and blurred vision.

 

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