WHY DO SHOES HAVE HEELS? DO THEY HELP IN WALKING?

The human foot is designed to walk on grassy or muddy surfaces not on hard concrete or marble. Walking barefoot on such hard artificial surfaces jolts our body and jars the spine. Heels on shoes provide cushioning to the body. The heel requires more cushioning than the rest of the foot because it bears the brunt of the impact with the ground.

In addition to cushioning the foot, the heel also ensures durability of the shoe. A shoe without a heel would soon wear out in the heel region. You can do it because your shoes cushion your feet from injury.

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WILL A PAPER IN A GLASS WATER REMAIN DRY?

What you will need

A wad of old newspaper, large plastic tub, glass tumbler, water.

What you do:

  • Fill the tub with water.
  • Scrunch up the newspaper and stuff it in the bottom of the glass tumbler. upside down to make sure that the paper does not slip out.
  • Holding the tumbler upside down, plunge it straight down to the bottom of the tub.
  • Pull out the glass from the water.
  • Do not tip the glass to the side at any time during the experiment.

What do you observe?

 When you take out the newspaper, you will find that it is absolutely dry!

Why does this happen?

 Air occupies space. When you submerge the tumbler, the air inside the glass cannot escape. It acts as a block, preventing the water from entering the glass. Hence the newspaper does not get wet.

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Does the water from a tap flow uniformly?

What you do:

  • Turn on the tap.
  • Watch the water flow.

What you see:

The stream of water is initially of the same size as the opening of the mouth of the tap but it decreases in size as it flows.

Why does this happen?

Surface tension tends to hold the water in a solid stream at the top but as it falls, its speed increases because of the pull of gravity.

When the flow of water is continuous, the amount of water passing through any point should be the same. The amount of flow is determined by the cross sectional area of the stream multiplied by the speed of flow of the water. As the speed of the water increases due to gravity. its size reduces.

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When you pour tea (water or any other liquid) from a vessel into a glass, you see bubbles on the surface of the tea inside the glass. Do these bubbles form every time you pour the tea?

What you need:

A glass and a vessel with tea What you do:

Hold the vessel high above the glass and pour the tea into it. What do you find? Bubbles form on the surface of the tea inside the glass. Next hold the vessel close to the glass and pour the tea into it.

What do you find?

Bubbles don't form on the surface of the tea inside the glass.

What's the reason?

Due to surface tension, the surface of a liquid behaves like a stretched membrane or skin'. When you pour tea into the glass while holding the vessel close to it the tea falling gently cannot penetrate the skin of the tea in the vessel. But when you pour it from a great height, it strikes the surface of the tea in the glass with great force. The skin breaks trapping air, which bubbles back to the surface.

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Is the air cooler when you blow with your mouth open wide or with pursed lips?

What you do:

• Open your mouth wide and blow air into your palm. Observe.

• Then purse your lips and blow air into your palm. Observe.

What you find:

The air is warmer when you blow with your mouth wide open.

Why?

The temperature of the air coming out of the open mouth is more or less the same as that of the body, and hence it is warm. When you purse your lips, the air gets compressed and comes out in a thin stream but once, outside, it expands and cools. Another reason for the difference is that the fast moving stream of air draws in cool air from the surroundings.

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When a cycle is moving at a great speed, will you be able to see the lower and upper spokes of the wheels clearly? Let's find out.

What you need:

A bicycle and a friend to ride it.

What you do:

 • Ask your friend to cycle fast.

• Watch the upper and lower spokes of the wheels.

What you find:

The spokes of the wheels that are below are clearly visible but the upper spokes are a blur. Does it mean that the top of the rolling wheels moves faster than the bottom?

Yes. This happens because while the wheels are rotating on their axle, they are also moving forward along with the axles. At the top, the two motions are in the same direction but at the bottom the rotation is in the reverse direction.

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How do artificial satellites work?


Artificial Satellites



Artificial satellites send signals. There are many different kinds of signals they send. Each carries a different type of information.



Some artificial satellites send their signals to radios, telephones, and television sets. These are called communications satellites. Ships, aircraft, and even some cars use navigation satellites to work out their location on Earth. Weather satellites take pictures of the movements of the clouds. Scientific research satellites send information about the universe. Scientists can use an earth observation satellite to look at Earth and find heavily polluted areas or damaged forests. Military satellites can send signals about the movement of missiles, ships, and soldiers.



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How do Telescopes work?


Telescopes make distant objects look bigger. Two main types of telescopes are refracting telescopes and reflecting telescopes.



A refracting telescope gathers light from a distant object and focuses it through two lenses. It has one big lens in front and a smaller lens you look through. The lens at the front usually has a bulge on both sides. It is thick in the middle and thin around the edges. This lens collects the light from a distant planet or star and forms an image of it in the telescope tube. The other lens, called the eyepiece, is like a very powerful magnifying glass. It makes things look much bigger.



A reflecting telescope uses a large mirror to collect the light, instead of a lens. The mirror is at the bottom end of the tube. The light from a star goes straight down the tube and strikes the mirror. Then the light is reflected up the tube. A smaller mirror reflects the collected light. The light comes out through a hole in the side of the tube, where the eyepiece is.



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Can you tell how computers work?



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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How computers are used in industry?



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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How radar works?



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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Do you know how a rocket works?



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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How ice is produced in a refrigerator?



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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When and where motion pictures were invented?



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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How a camera works?



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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