My Science School

All computers work in basically the same way. They follow a set of instructions called a program that enables them to do calculations on information fed into them.

This process produces a result that is used in some way. The great advantage of computers over other machines is that the program can be changed, so that a computer can be given a wide variety of tasks to perform.

Computers consist of four main units – an input unit, a central processing unit is at the centre of operations and generally consists of a microchip located in the computer case. It controls the operations of all other units, which may be part of the computer or connected to it.

The input unit is used to feed information or data into the computer. It is usually a keyboard, but it may also be a light pen that interacts with a computer screen, or simpler devices such as a joystick, a mouse or a bar-code reader. The keyboard is also used to write programs.

The central processing unit first passes the information to the internal memory, where it is held temporarily. The program is also held in the memory, and the processing unit follows the program to produce the results. These go to the output unit, which is usually a video screen or printer, or they may be sent along telephone lines to other computers.

The computer also has an external memory unit such as disc drive that takes programs and data from the internal memory and records them for use at a later date.

 

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The electronic computer is used in many fields of activity and is extremely valuable in doing complicated work accurately and quickly. It has removed much of the drudgery from such routine tasks as telephone se wonderful machines work? We can see in the simple example of checking the stocks held by a warehouse.

In large scale industries it costs a great deal of money to keep a large number of goods in store. Nevertheless a company must always know how many goods it has at a given time in case it runs out of any item. So there must always be a reserve level below which stocks must not go. When that level is reached the company orders more goods to be delivered.

One way of keeping a check is to use a punched-card system. Each article which is delivered to the warehouse has its own card punched with required information which may relate to style, colour, price, size or other relevant details, and this is fed into computer.

When the article is sold and leaves the warehouse the computer is fed with this information too. At any time the computer can show exactly how many of those articles are in stock and if the stocks have to be replenished. The computer does this job with great speed and accuracy and can give an account of exactly how many articles of many different types are in stock.

The initial effect of computers is as an efficient means of performing complicated or routine tasks. In the long term, however, they will make new and different activities possible for instance, education and many occupations will be greatly affected as methods of storing and retrieving vast quantities of information are further developed.

 

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We have all at one time or another heard the echo of our own voice. An echo is caused by sound waves being bounced back from a solid obstacle, rather like a rubber ball bouncing off a wall. The same thing happens to radio waves which are sent out by a powerful transmitter. When the waves collide with a solid object they bounce back and can be picked up by a receiving set which is usually located at the same place as the transmitter. Since the speed of these waves is known we can tell how far away the obstacle is by calculating how long the waves take to cover the distance. This is how radar works.

The word ‘radar’ is an abbreviated form of the name ‘radio detection and ranging’. Radar is now used everywhere’ at airports, missile bases, space centers for following and tracking satellites and on ships and tracking satellites and on ships and aircraft for automatic navigation. A simple form of radar is used by police to detect speeding vehicles.

 

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You may have seen a certain type of lawn sprinkler which works by spinning round and round as the water squirts from it. The spinning movement is caused by the pressure of the water pushing against the movable arm of the sprinkler.

Sir Isaac Newton noticed something like this happening and it led him to discover an important law of nature. Newton’s law was that for every action in one direction there is an equal action in an opposite direction. In the case of the lawn sprinkler the water goes in and pushes in one direction and the sprinkler turns in the opposite direction.

The same law explains why a rifle recoils sharply when it is fired. The firing of the gun is known as the action and the recoil of the gun is the reaction.

The principle is what makes rockets speed through the air. Rockets are fuelled by very highly compressed gases. When these gases are violently released from the tail of the rocket the reaction they set up gives the rocket a mighty push in the direction opposite to the gas flow.

The greater the distance to be travelled, the greater must be the initial thrust. When Saturn V was launched, for example, its five engines consumed kerosene and liquid-oxygen at rate of 15 tons per second.

 

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It was far more difficult for man to discover how to produce artificial cold than it was for man to discover how to produce artificial cold than it was for him to produce warmth.

In olden days man tried to keep things cool during the summer by using snow or ice. This was a very difficult process. The snow and ice had to be carried down from the high mountain tops and stored in specially built places.

The ancient Romans, for example, brought their snow and ice from the Apennine Mountains. They dug large chambers in the ground which they called officinae reponendae nivis. This meant snow store. The store was covered in wooden boards and the ice was brought to the towns from the Apennine region near Rome and in Sicily from Mount Etna.

The first Experiments to produce ice artificially began in the seventeenth century. It was later discovered that in specified condition certain substances changed from a solid into liquid state. This fusion, or melting process, was found to be caused through the absorption of heat by those substances. As the heat was absorbed it was accompanied by a steady cooling of the temperature. Further experiments showed that the same absorption of heat could be carried out by evaporating and liquid. An example of this is when a sudden breeze evaporates the perspiration from our faces and makes us feel quite chilly. It is on this principle of heat absorption that ordinary household refrigerators work. The most commonly used liquid to bring about cooling is ammonia gas in solution. This solution runs through coiled tubes. It starts as a liquid and through compression becomes a gas which absorbs the surrounding warmth. This process is repeated over and over again until ice begins to form.

The first household refrigerator was made early in the nineteenth century. Since 1918 their use has becomes more and more widespread.

 

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In 1831 the Belgian physicist Joseph Plateau produced an apparatus which he called the phenakistoscope. This was followed by other devices such as the zoetrope or ‘wheel of life’ of the British inventor William Horner in 1834 and praxinoscope of the Frenchman Emile Reynaud in 1880. Despite their difficult names these apparatuses were all fairly simple and they all exploited a certain characteristic of the human eye.

If an object is placed before our eye its image is picked up by the retina, an extremely sensitive screen inside the eyeball. Every change of object outside causes a change in the image received by the retina and if the changes are rapid enough a whole line of images can blend into one. In the phenakistoscope and the other machines a series of image showing the various stages of a person in movements were shown on a revolving drum. All the images ran together and the viewer received the impression of continuous movement. Modern animated cartoons are also produced by rapid succession of drawings.

An important development in motion pictures took place in 1889 when the famous American inventor Thomas Edison, succeeded in using photographs instead of drawings. The photographs were taken one after the other on one roll of film. Edison then invented the Kinetoscope to show his moving pictures. This was kind of peep-show device which showed viewer about fifteen seconds of life-like movements.

The first truly modern cinematographic machine was produced in 1895. In that year the brothers Auguste and Louis Lumiere of France patented their famous and historic ‘cinematograph’.

 

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A camera is a fairly simple piece of equipment in its basic structure. One must not be put off by the numerous levers, buttons, scales and other gadgets on the outsides. These are all extremely useful aids but are not completely essential.

The essential part of the machine is what gives its name: the camera obscura. This is Latin for dark room. Photographs are produced when rays of lights penetrate into this dark chamber. The light must enter through a small opening and strike against a sensitive film. The surface of the film is covered in an emulsion of chemicals which capture the images being carried by light rays. The small opening, or aperture, must also be able to open the aperture to let the light in. this mechanism is called the shutter. In a simple camera this is about the only moving part.

In more expensive cameras the fitting includes mechanism which can vary the exposure time which determines how long the shutter will stay open. The can range from a thousandth of a second for fast-moving subjects to one second or more for still dimly-lit scenes. Other controls include an aperture selector to vary the amount of light passing through the lens, and a focusing mechanism to produce a sharp image.

The camera obscura has long been known to man and Leonardo da Vinci made accurate drawings of it in the fifteenth century. It was not until 1839, however, that the first commercially available cameras were made in Paris by Alphonse Giroux for Daguerre.

 

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When the first railway began to operate it was suggested that a messenger should ride on a horse ahead of the train to tell people of its approach and warn the engine driver of any obstacles along the track.

Soon the train was able to travel much faster than the horse. Men with flags stood beside the track and either signaled the train-driver to stop or waved him on.

The problem of travel safety grew as trains increased in speed and numbers and level crossing with gates were built as well as viaducts to take trains over dangerous or difficult places.

Eventually a comprehensive system of mechanical signaling was evolved. Semaphore signals that swung up or down on a tall pole beside the track were the most common. Nowadays the majority of large railway stations have colour-lights signals, with red meaning ‘stop’ , green ‘go’ and amber ‘caution’.

All these signals are now worked electrically. It is no longer necessary for a man with a watch to check the various times when trains pass, open gates or decides which track the train will go on to and make a note of trains which have been delayed. Today all these tasks are done by computers and the signal posts of large stations are completely automated.

 

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Sometimes films are shots or photographed without sound: the dialogue is added later together with sound effects and other noises. When these sounds are added the noise of a waterfall might be produced by merely shaking water about in a basin or the voice of a stage actor might replace that of the film actor in a process known as dubbing.

The major developments in cinematography were the introduction of sound in 1927 and the advent of colour photography.

The cinema really grew up as an art after the Second World War but it found an extremely dangerous rival in television. So the film industry began to think up counter attraction. These included the evolution of wide screens as in the processes known as Cinema Scope and Cinerama. In wide-screen presentations, a special lens may be used that spread out the image on the film to fill the screen. When the film is shot, a similar kind of lens is used to squeeze a wide field of view on to standard film. Modern cinemas in addition may also use stereophonic sound which is emitted by numerous loudspeakers. This gives the audience the impression that they are might in the middle of what is happening.

The story of the cinema is not yet finished. Scientists are studying a way of producing satisfactory three-dimensional films so that the images are no longer flat. Experimental have also been carried out with a circular screen that completely surrounds the audience.

 

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The first step towards making a film is the idea for the subject. The next requirement is money to pay for all the production costs. The producer is the man who raises this money and generally he chooses the director, the most important man in making a film. The director then appoints a writer to prepare a screenplay which is like a stage play but consists of hundreds of short scenes which finally make up the whole film.

A film studio seen for the first time is quite an overwhelming sight. You may see a straight road lined with marble columns representing a roman road of 2000 years ago. Near this scene there might be a ramshackle prairie town of the Wild West. In another part of the studio there may be a magnificent governor’s palace set in imperial India. The studio is therefore crowded with Roman soldiers or gladiators, cowboys or young English colonial ladies. Some part of the studio will probably be very strictly cordoned off because a film crew may be ‘shooting’ there.

Today film directors prefer to work on location which means they film their scenes in real places outsides instead of creating them from plaster and wood inside a studio. Other film crews with their actors and actresses travel from one continent to another. But when a film is historical or period piece it is usually shot inside a studio. Films employ armies of technicians. Skilful carpenters and scene painters build intricate structures known as sets which can be of medieval castles, or of ultramodern apartments.

 

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Modern science and technology have made it possible, among other wonderful things, to make a permanent record of sounds and human speech. The tape in a tape recorder is made of an insulation material on which a thin magnetic layer has been placed. The tape is normally 3 millimeters wide in cassettes and 6 millimeters in reels. How does a tape recorder work?

There is a motor which turns a reel of tape from the supply wheel to the take-up reel. The tape passes across the recording head. When we speak into the microphone the voice is turned into a series of electrical impulses. These impulses are caught on the tape in various patterns. In video tape recordings the light signals are turned into electrical impulses recorded on the tape.

When the tape is played back it runs past an electromagnet. The magnetic patterns that have been recorded along the magnetized tape set up a variable magnetic field with the electromagnet.

The impulses of this magnetic field are the converted into sounds which are amplified and played through a loudspeaker to re-emerge as the original speech or music that was first fed into the tape recorder.

Today tape recorders are very popular. Besides being easy to operate they have the added advantage that recordings can be erased and the tape used many times. A new compact type of tape recorder is the cassette recorder. The works on the same principle but use narrower tape in its own self-contained cassette.

 

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 Even air has weight and, like any solid object, it presses down on the surface of the Earth. Scientists decided to measure the amount of his pressure and the Italian Galileo was the first to succeed. He used a very long tube, closed at one end, which he filled with water and then placed the open end in a receptacle full of water. The water in the tube fell, stopping at a height of 10 meters. A few years later, in 1643, a pupil of Galileo named Evangelista Torricelli carried out further experiments using a heavier liquid than water; mercury. The mercury rose inside its tube, closed at one end, which he filled with water and then placed the open end in a receptacle full of water. The water in the tube fell, stopping at a height of 10 metres. A few years later, in 1643, a pupil of Galileo named Evangelista Torricelli carried out further experiments using a heavier liquid than water: mercury. The apparatus was given the name barometer from, the Greek baros meaning ‘weight’ and metron meaning ‘measure’. Torricelli soon noticed that the height of the mercury column varied with changes in air pressure. About 1647 Blaise Pascal’s experiments finally convinced people of the correctness of Torricelli’s ideas.

The most modern form of this instrument is the aneroid barometer, from Greek a meaning ‘without’ and neros meaning ‘liquid’. The aneroid barometer consists of a small steel box which contains a vacuum. The pressure of the air outside the box can cause the surface of the box to move in or out. A needle on the dial records the movements of the box along a graduated scale to show the changes in air pressure.

This type of barometer is smaller and more portable than a mercury barometer but it is not quite as accurate. It has first to be calibrated or set to a mercury barometer before it can be used.

 

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