Pedal power
Riding a bicycle is a perfect way to find out about force. When you are moving at a steady speed the force produced by your legs exactly balances friction, the force that tries to slow you down. You can never get rid of friction, but you can reduce it by keeping the bike oiled and your head down so that you lessen the friction caused by the air you push of the way.
1. Going up
When you go uphill, you have to counteract the downward force of gravity. The bike starts to slow down unless you put in extra work to match the downward pull.
2. Going down
Going downhill is easy, because this time gravity is on your side. If you freewheel and keep your hands off the brakes, the bike starts to speed up. It keeps speeding up until friction matches the pull of gravity.
3. On the level
On flat ground, gravity has no overall effect. To keep going at a steady speed, all you have to do is match the force of friction. Some of the friction is produced by the moving parts of the bike. The rest of it is produced by the air you push out of the way. If you go really fast, 'air resistance gets very large.
4. Time to Stop
As soon as you stop pedalling, friction and air resistance gradually bring the bike to a halt. Another form of friction, jamming on the brakes, stops the bike much more quickly.
Saturday, November 17, 2007
Staying on course
Once something is on the move, it will keep moving a straight line. This is why passengers are thrown forwards when a car brakes. It is also why water stays in a bucket if you whirl it around in a circle, while the bucket turn a corner, the water tries to continue straight on.
Strapped in
Seat belts bring people to a safe halt if a car stops suddenly.
How to lose weight
Because the Earth is not exactly round, the force of gravity varies slightly fro place to place. If you weight 30 kg (66 lb) at the North Pole, you would find that you weighed only 29.85 kg (65.8 lb) at the Equator.
Once something is on the move, it will keep moving a straight line. This is why passengers are thrown forwards when a car brakes. It is also why water stays in a bucket if you whirl it around in a circle, while the bucket turn a corner, the water tries to continue straight on.
Strapped in
Seat belts bring people to a safe halt if a car stops suddenly.
How to lose weight
Because the Earth is not exactly round, the force of gravity varies slightly fro place to place. If you weight 30 kg (66 lb) at the North Pole, you would find that you weighed only 29.85 kg (65.8 lb) at the Equator.
Friday, November 16, 2007
FORCE AND MOTION
Force are at work all around us. They provide the push that gets things moving, but also include friction, the force that slows them down. They can make a jumbo jet hurtle down a runway and into the skies, or pull a snowflake towards the ground. Forces can also make things change direction, and they can stretch, squash and bend them out of shape. We cannot see forces themselves, but we can see and feel what they do.
How does gravity work?
We know what gravity feels like, but it is still a mysterious force.Everything in the Universe, even your own body, attracts other objects toward it. When you stand on the ground, the Earth attracts your body and your body attract the Earth. Because the Earth is so huge, its gravitational pull keeps you on the ground.
How does gravity work?
We know what gravity feels like, but it is still a mysterious force.Everything in the Universe, even your own body, attracts other objects toward it. When you stand on the ground, the Earth attracts your body and your body attract the Earth. Because the Earth is so huge, its gravitational pull keeps you on the ground.
Copper
A reddish metal, is one of the few elements that is sometimes found in a pure form, rather than being mixed with other elements in a compound.
Carbon atom
This is a single atom of carbon. In the middle, it has a nucleus made of six neutrons. Six tiny particles called electrons spin around them. Carbon atoms are good at making molecules, because they can link up with lots of other atoms. As well as plastics, they are found in thousands of other substance, including most of the ones in living things.
A reddish metal, is one of the few elements that is sometimes found in a pure form, rather than being mixed with other elements in a compound.
Carbon atom
This is a single atom of carbon. In the middle, it has a nucleus made of six neutrons. Six tiny particles called electrons spin around them. Carbon atoms are good at making molecules, because they can link up with lots of other atoms. As well as plastics, they are found in thousands of other substance, including most of the ones in living things.
Thursday, November 15, 2007
Atoms and elements
Most substance contain a mixture of different atoms. Element are different, because they contain one type of atom and nothing else. Most elements are metals but some are gases, such as oxygen, and others are nonmetals, such as sulfur. Elements generally combine with other elements, making chemical compounds, such as water, sugar and salt. Altogether, 92 elements exist naturally on Earth, but scientists have made about 20 additional elements in laboratories.
Most substance contain a mixture of different atoms. Element are different, because they contain one type of atom and nothing else. Most elements are metals but some are gases, such as oxygen, and others are nonmetals, such as sulfur. Elements generally combine with other elements, making chemical compounds, such as water, sugar and salt. Altogether, 92 elements exist naturally on Earth, but scientists have made about 20 additional elements in laboratories.
Why are some things heavier than others?
It is easy to pick up a big block of polystyrene foam, but hard to pick up even a brick-sized limp of lead. The reason for this is that an object's weight depends partly on what kind of atoms it contains, and partly on how closely they are packed together. Polystyrene foam has light atom, tightly packed together. Compared to polystyrene, it is very dense : 1 m3 (35 cu ft) of polystyrene foam weight foam about 5 kg (11 lb), while 1 m3 of lead weights about 11 tonnes - over 2000 times as much.
What's inside an atom?
Scientists use to believe that atoms were the smallest things in the Universe. They thought that because atoms could not be split up into anything smaller. But things are not nearly as simple as this: atoms contain other particles that are much smaller than they are. Particles called protons and neutrons make up the centre, or nucleus, of each atom. Around them are electrons - particles that hurtle around the nucleus like planets orbiting the Sun. The smallest atoms, belonging to hydrogen, contain only one proton and one electron. The biggest, belonging to metals like uranium, contain over 200 protons and neutrons, and over 90 electrons.
It is easy to pick up a big block of polystyrene foam, but hard to pick up even a brick-sized limp of lead. The reason for this is that an object's weight depends partly on what kind of atoms it contains, and partly on how closely they are packed together. Polystyrene foam has light atom, tightly packed together. Compared to polystyrene, it is very dense : 1 m3 (35 cu ft) of polystyrene foam weight foam about 5 kg (11 lb), while 1 m3 of lead weights about 11 tonnes - over 2000 times as much.
What's inside an atom?
Scientists use to believe that atoms were the smallest things in the Universe. They thought that because atoms could not be split up into anything smaller. But things are not nearly as simple as this: atoms contain other particles that are much smaller than they are. Particles called protons and neutrons make up the centre, or nucleus, of each atom. Around them are electrons - particles that hurtle around the nucleus like planets orbiting the Sun. The smallest atoms, belonging to hydrogen, contain only one proton and one electron. The biggest, belonging to metals like uranium, contain over 200 protons and neutrons, and over 90 electrons.
Wednesday, November 14, 2007
THE MADE OF THE WORLD
Everything around us, including our own bodies, is made of specks of matter called atoms. There are many different kinds of atoms, but all of them are extremely small. They are so tiny that even something as small as a sugar cube contains about half a billion of them, packed closely together. If the atom in just one sugar cube were shared out among the entire human population of the world, we would each have about 100 million of them.
What happens when something melts?
In solid substances, such as ice, molecules are packed closely together. Forced hold neighbouring molecules together, which makes the material hard. But if you warm a piece of ice, the forces start to weaken, the molecules drift apart, and the ice starts to melt. If the heat is maintained, the molecules move faster and faster, until they are moving so quickly that they escape into the air. The water turns into steam, and eventually all of it disappears. If the steam is cooled, the molecules slow down. It turn back into water, then if it gets cold enough, back into ice.
In steam, molecules move about quickly. In liquid water, they move more slowly and are closer together. In ice, they are packed together to make crystals
What happens when something melts?
In solid substances, such as ice, molecules are packed closely together. Forced hold neighbouring molecules together, which makes the material hard. But if you warm a piece of ice, the forces start to weaken, the molecules drift apart, and the ice starts to melt. If the heat is maintained, the molecules move faster and faster, until they are moving so quickly that they escape into the air. The water turns into steam, and eventually all of it disappears. If the steam is cooled, the molecules slow down. It turn back into water, then if it gets cold enough, back into ice.
In steam, molecules move about quickly. In liquid water, they move more slowly and are closer together. In ice, they are packed together to make crystals
INTRODUCTION
Science and technology is a field of history which examines how humanity's understanding of the natural world - science, and ability to manipulate it - technology, have changed over the millennia. This field of history also studies the cultural, economic, and political impacts of scientific innovation. Below is a main point of the science and technology resource :
- Made of the world
- Force and motion
- Energy and heat
- The visible energy of light
- The making waves of sound
- Electricity and magnetism
- Telephone and fax
- Recording of sound
- Radio communications
- Microscopes and telescopes
- Photography
- Television and video
- Computers and electronics
- Working robots
- Laser light
- Printing and publishing
- Space satellite
- Cars and bicycles
- Age train
- Ships and seafaring
- Balloons and airships
- The work of aeroplanes
- Space travelling
- Food technology
- Generating energy
- Houses and buildings
- Bridges, dams and tunnels
- Information of revolution
Also see the fact file of science and technology here :
- Building and engineering
- Elements and materials
- Transport
- Invention and discoveries
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