My Science School

We usually see light as white, but it is actually a mixture of different colours. We know this because we can see the colours in a rainbow. When the Sun is shining low in the sky behind you and rain is falling in front of you, you may see a rainbow.

The colours of a rainbow

The colours always spread out in the same order. We call the pattern they make a spectrum. The seven main bands of colour blend into each other, creating millions of different colours.

Seeing a rainbow

As sunlight passes through a shower of raindrops, it bends and splits into different colours.

Double rainbow

If the sunlight is reflected twice inside each raindrop, you can see a see rainbow outside the main one, with its colours in the opposite order.

Colour arc

Rainbows are curved because the colours leave the raindrops at different angles.

Bright colours

Large raindrops from bright, clear rainbows, while small raindrops make faint, fading ones.

Is it the end?

If the ground wasn’t in the way, you would see the rainbow as a circle.

Inside a raindrop

Rays of sunlight shine towards the falling raindrops. When a ray enters a raindrop, it bends and the white light spreads into different colours. The light reflects off the back of the raindrop. When the light leaves the raindrop it bends again, so the colours spread out even more and shine down towards your eyes.

 

Picture Credit : Google

Light is a type of energy that allows us to see things. Light travels as rays, in straight lines. Light rays are given off by things that glow, such as the Sun, a candle, or a light bulb. These things are called light sources. Other objects around us look bright because they bounce light from light sources back to our eyes. When there is no light source everything looks dark, for example at night.

Seeing things

Most things do not give out their own light. We can see these objects when we look at them because they reflect the light that falls on them. Light from a light source, such as the Sun, bounces off the object and into our eyes.

Creating shadows

If something solid gets in the way of light coming from a source, the light rays are blocked. This creates a shadow behind the object, which is the same shape as the object.

Shadow length

The length of the shadow of an object can change, depending on where the light source is. The more directly above an object a light source is, the shorter the object’s shadow will be.

Midday

At midday, the Sun is almost directly overhead. The light rays from the Sun can reach most of the ground on the far side of the ball, forming a short shadow.

Late afternoon

By late afternoon, the Sun is low in the sky. The light rays from the Sun are blocked from reaching a large area of ground on the far side of the ball, so a long shadow forms.

 

Picture Credit : Google

Vibrations with lots of energy produce big waves and make loud sounds. So, banging a drum harder will produce a louder sound. Sound waves lose energy as they travel, which means that the further you are from a sound, the quieter it will be.

Rustling leaves

When leaves brush against one other, they produce tiny vibrations in the air. These vibrations only have a small amount of energy, so the rustling sound is very quiet.

Roaring lion

A lion’s roar causes the surrounding air to vibrate with lots of energy. It produces a loud sound, which can be heard up to 8 km (5 miles) away.

Rocket launch

When a rocket launches, the exploding gases produce huge amounts of sound energy. The noise is louder than 10 million rock bands performing at once!

 

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Sound is produced when things vibrate, or shake. A vibrating object makes the air next to it vibrate as well. These vibrations travel through the air as a sound wave, which we hear with our ears. Sound waves can also travel through liquids and solids, such as water, rock, or wood.

Making sound

When the climber hits the metal spike with his hammer, it vibrates. This vibration causes the surrounding air to vibrate too, producing a sound wave.

Sound wave

The sound wave spreads out through the air. It travels away from the rock and hammer until it reaches a solid surface.

Reflection

When the sound wave hits a solid surface, such as the side of a cliff, some of the energy becomes back towards the climber. The rest of the sound energy travels through the rock.

Echo

The climber will hear the reflected sound wave as an echo, a few moments after he first produced the sound.

 

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Heat is a type of energy that we can feel. The hotter something is, the more heat energy it gives out. Heat energy always tries to spread from a hotter to colder things. So, when you touch a hot object, heat energy flows out of the object into you, warming you up.

Conduction

Heat energy spreads out through solid objects by conduction. Metal objects are very good conductors of heat, so heat energy pass through them quickly and easily.

Convection

When gases and liquids get hot, heat energy spreads out through them by convection. Hot air or water rises, and cold air or water sinks to take its place.

Radiation

Heat escapes from the surface of hot objects by invisible rays that travel through air and space. This is how we feel the heat from the Sun. hotter objects give out more radiation than cooler ones.

Temperature

Temperature is the measure of how hot or cold things are. It is recorded in degrees Celsius (ºC) or degrees Fahrenheit (ºF).

15 millionºC (27 millionºF)

The temperature at the centre of the Sun.

1760ºC (3,200ºF)

The temperature at which sand melts and turns into glass.

232ºC (450ºF)

The temperature at which dry wood catches fire.

100ºC (212ºF)

The boiling point of water.

56.7ºC (134ºF)

The hottest temperature recorded on Earth at Death Valley, California, USA, on 10 July 1913.

37ºC (98.6ºF)

The average temperature of the human body.

2ºC (35.6ºF)

The temperature of the air when rain turns to snow.

0ºC (32ºF)

The freezing point of water.

89.2ºC (-128.5ºF)

The coldest temperature recorded on Earth at Vostock Station, Antarctica, in 1983.

-272ºC (-458ºF)

The temperature of the Boomerang Nebula, a cloud of dust and gas that is the coldest place in the Universe.

 

Picture Credit : Google

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.

 

Picture Credit : Google