Making colours
A beam of sunlight contains all the colours of the rainbow. When it shines onto something with lots of narrow lines, like a CD, the different colours are separated, so that they can be seen. This is called diffraction. Some birds and butterflies get their colour in this way.
What makes a rainbow?
Rainbows appear when the Sun is shinning and there is rain in the air. The falling drops split the Sun's light into seven different colours, and reflect it towards your eyes. The rainbow you see is always a 'private' one, even if someone is standing close to you, they see a rainbow made by a different set of raindrops. No matter how hard you try, you can never see a rainbow from the side or from behind, and you can never get to the rainbow's end. If you move, the rainbow moves too.
Saturday, November 24, 2007
Home light show
Scientists investigate light with complicated pieces of equipment, but you can make a start with the everyday objects shown here. If you put them on a tabletop on a sunny day, you will be able to see how light it can be broken up into different colours and how it casts shadows.
How fast does light travel?
Nothing moves faster than light, 299 792 km (186 287 miles) a second. It travels from the Sun to the Earth in around eight minutes, and it can cross the average room in about one hundred-millionth of a second. When light shines through transparent matter such as glass, it slows down by up to a third, but even then, it is still faster than anything else.
Scientists investigate light with complicated pieces of equipment, but you can make a start with the everyday objects shown here. If you put them on a tabletop on a sunny day, you will be able to see how light it can be broken up into different colours and how it casts shadows.
How fast does light travel?
Nothing moves faster than light, 299 792 km (186 287 miles) a second. It travels from the Sun to the Earth in around eight minutes, and it can cross the average room in about one hundred-millionth of a second. When light shines through transparent matter such as glass, it slows down by up to a third, but even then, it is still faster than anything else.
Friday, November 23, 2007
Why can't you see around corners?
You can hear around corners because sound spreads in all directions, but you cannot see around them because light nearly always travels in straight lines. One way of getting around this is to use a mirror. This reflects the light around the corner, so you can see what, or who, is hiding behind it.
Light you cannot see
If the beam of light shone past your nose in completely empty outer space, you would not be able to see it. The reason for this is that you can see light only when it shines into your eyes. On Earth, you can see beams from the side because dust and air scatter some of the light your way.
You can hear around corners because sound spreads in all directions, but you cannot see around them because light nearly always travels in straight lines. One way of getting around this is to use a mirror. This reflects the light around the corner, so you can see what, or who, is hiding behind it.
Light you cannot see
If the beam of light shone past your nose in completely empty outer space, you would not be able to see it. The reason for this is that you can see light only when it shines into your eyes. On Earth, you can see beams from the side because dust and air scatter some of the light your way.
THE VISIBLE ENERGY OF LIGHT
Light is the only kind of energy that we can see. It moves about a million times faster than sound, and it can travel through empty space. Some things, like the Sun, make light. But most of the things we see do not. Instead, they reflect some of the light that falls on them. Light normally travels in straight lines, but it can be made to change course, and it can be split up into different colours.
Why is light made of?
Light is pure energy. You cannot touch it or pick it up, but whenever it shines into your eyes, you can see that it is there.Light energy travels in pulse called waves, and the distance between the wave decides its colour. In blue light, for example, the wave are about 0.0005 mm (0.00002 in) apart, roughly 200 times narrower than a human hair. Light belongs to a whole family of waves that includes X-rays, microwaves and radio waves.
Why is light made of?
Light is pure energy. You cannot touch it or pick it up, but whenever it shines into your eyes, you can see that it is there.Light energy travels in pulse called waves, and the distance between the wave decides its colour. In blue light, for example, the wave are about 0.0005 mm (0.00002 in) apart, roughly 200 times narrower than a human hair. Light belongs to a whole family of waves that includes X-rays, microwaves and radio waves.
Thursday, November 22, 2007
Demolition job
One way to demolish a tower block is to knock it down bit by bit. A much speedier way is to use explosives to release a burst of energy, bringing the building crashing to the ground. Below is how potential energy turns into other kinds of energy, and the dramatic results of the changes.
1. Potential energy is stored energy. Before the bang, there is potential, energy in the explosives, and in the tower block, because it contains heavy materials perched high above the ground
2. When the explosion takes place, the explosives potential energy is changed into heat, movement and sound. The tower block's potential energy also changes into movement and sound, as thousands of tons of concrete and steel come crashing down.
3. When the dust settles after the explosion, the potential energy in the explosives and the tower block has been changed. Most of it has been converted into different kinds of energy, which have escaped into the air.
One way to demolish a tower block is to knock it down bit by bit. A much speedier way is to use explosives to release a burst of energy, bringing the building crashing to the ground. Below is how potential energy turns into other kinds of energy, and the dramatic results of the changes.
1. Potential energy is stored energy. Before the bang, there is potential, energy in the explosives, and in the tower block, because it contains heavy materials perched high above the ground
2. When the explosion takes place, the explosives potential energy is changed into heat, movement and sound. The tower block's potential energy also changes into movement and sound, as thousands of tons of concrete and steel come crashing down.
3. When the dust settles after the explosion, the potential energy in the explosives and the tower block has been changed. Most of it has been converted into different kinds of energy, which have escaped into the air.
What happen to energy after it is used?
No matter how many times energy is changed, it can never be destroyed. But whenever it changes, some of it always escapes. For example, a car engine turns much of the potential energy in petrol into movement. But it also turns some of it into noise and heat, and this escapes as the car moves along. No matter how well machines are designed, they always waste some of the energy that they release.
A waste of energy
As a workman digs a hole with a pneumatic drill, energy escapes in the form of noise and heat, this energy cannot be used.
Energy in a raindrop
The amount of energy in a falling raindrop is about 175 thousand billion times less than the amount of energy of a cruising jumbo jet. But added together at any one time, the energy in all the raindrops falling on Earth is much greater than the energy of all the planes in the air.
No matter how many times energy is changed, it can never be destroyed. But whenever it changes, some of it always escapes. For example, a car engine turns much of the potential energy in petrol into movement. But it also turns some of it into noise and heat, and this escapes as the car moves along. No matter how well machines are designed, they always waste some of the energy that they release.
A waste of energy
As a workman digs a hole with a pneumatic drill, energy escapes in the form of noise and heat, this energy cannot be used.
Energy in a raindrop
The amount of energy in a falling raindrop is about 175 thousand billion times less than the amount of energy of a cruising jumbo jet. But added together at any one time, the energy in all the raindrops falling on Earth is much greater than the energy of all the planes in the air.
Wednesday, November 21, 2007
How hot or cold can things become?
There is no limit to how hot things can become, but if something becomes extremely cold, its atoms stop moving. It cannot get any colder. Scientists have come close to reaching this temperature, called absolute zero, at -273.16 Celsius (-459.69 Fahrenheit). Near absolute zero, matter starts to behave in strange ways. Some gases turn into metals, and some metals become 'superconductors' This means that electricity can flow through them forever, without needing any energy from outside.
There is no limit to how hot things can become, but if something becomes extremely cold, its atoms stop moving. It cannot get any colder. Scientists have come close to reaching this temperature, called absolute zero, at -273.16 Celsius (-459.69 Fahrenheit). Near absolute zero, matter starts to behave in strange ways. Some gases turn into metals, and some metals become 'superconductors' This means that electricity can flow through them forever, without needing any energy from outside.
What happens when things get hot?
Heat is one of the most important forms of energy. When something warms up, the atoms inside it start to move more quickly, and they also spread farther apart. The hotter something is, the faster its atoms move. When atoms become really hot, they start to give out light. First they glow dull red, but if they get even hotter they turn bright red, yellow, white and finally blue. Heat is a bit like water, because it always flows 'downhill'. That is, it moves from warm things to cool things, but never the other way round. Things feel hot when some of their heat energy travels into your skin, and they feel cold when heat energy flows from you into them.
Heat is one of the most important forms of energy. When something warms up, the atoms inside it start to move more quickly, and they also spread farther apart. The hotter something is, the faster its atoms move. When atoms become really hot, they start to give out light. First they glow dull red, but if they get even hotter they turn bright red, yellow, white and finally blue. Heat is a bit like water, because it always flows 'downhill'. That is, it moves from warm things to cool things, but never the other way round. Things feel hot when some of their heat energy travels into your skin, and they feel cold when heat energy flows from you into them.
Tuesday, November 20, 2007
ENERGY AND HEAT
Energy makes thing happen. Without it, the entire Universe would be cold and dark, and nothing would be able to move. There are many kinds of energy, including heat, light sound and electricity. Each time we use energy, it changes from one form into others. For example, when you turn on a light, electrical energy is changed into light and heat, and when you flick the pages of this book, chemical energy from the food you eat is changed into movement.
Energy from the Earth
Plants need sunshine to grow, and animals need plants for food. If the Sun went out tomorrow, plants and animals would should die, but some bacteria would still survive because they get their energy from chemicals inside the Earth. They live in hot springs and deep-sea vents (holes in the Earth's crust) where water brings the chemicals to the surface.
Energy from the Earth
Plants need sunshine to grow, and animals need plants for food. If the Sun went out tomorrow, plants and animals would should die, but some bacteria would still survive because they get their energy from chemicals inside the Earth. They live in hot springs and deep-sea vents (holes in the Earth's crust) where water brings the chemicals to the surface.
Monday, November 19, 2007
Superhuman strength
The human body is good at some tasks, but not so good at others. However, with the help of pulleys, levers, ramps and gears, we can do things that seem impossible, like lifting a car off the ground. Devices like car jacks all work by reducing the force you need to do a job, while increasing the amount of movement you have to carry out.
The human body is good at some tasks, but not so good at others. However, with the help of pulleys, levers, ramps and gears, we can do things that seem impossible, like lifting a car off the ground. Devices like car jacks all work by reducing the force you need to do a job, while increasing the amount of movement you have to carry out.
Sunday, November 18, 2007
Sliding along
When an object slides past another, friction slows it down. You can test this with two sheets of sandpaper. If you try to slide their sanded sides over each other, you will find that friction make it hard work. If you turn the sheets over, the smooth side make the job easier. With slippery surfaces, such as ice or snow, there is so little friction that things slide along very fast. This helps skiers and bobsleighers to reach speeds over 200 km/h (125 mph).
When an object slides past another, friction slows it down. You can test this with two sheets of sandpaper. If you try to slide their sanded sides over each other, you will find that friction make it hard work. If you turn the sheets over, the smooth side make the job easier. With slippery surfaces, such as ice or snow, there is so little friction that things slide along very fast. This helps skiers and bobsleighers to reach speeds over 200 km/h (125 mph).
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