My Science School

               The word ‘ceramics’ has its origin in the Greek word Keramos, which means “potter’s clay”. Today the word refers to all types of pottery, whatever its composition or use. All ceramics are made from various clays, together with materials such as flint, felspar or china clay.

               However, strictly speaking ceramics are compounds of silicon, carbon, oxygen and nitrogen combined with other elements like sodium, potassium, calcium, barium etc. The principal raw material used in the manufacture of ceramics is clay. These clays are formed by decomposing natural rocks which are exposed to the wearing action of air and water. Granite is the rock which provides the bulk of useful clays. It is composed of quartz, mica, felspar etc. These clays are crushed and ground into fine particles. The particles are mixed and moisted with right proportion of water, which makes the particles flexible for shaping. Different methods are used for getting the desired shape.

               After the product has dried, it is heated. This process takes place in a special type of furnace called kiln. Ceramics are heated at temperatures ranging from 650°C to 1650°C. Firing makes the products hard in the desired shape and turns their glaze into a smooth coat. This process also makes the product leak-proof, durable and decorative.

               Clay and shale are used to make building products, such as bricks and drain pipes. Calcium silicates are used in making the cement. Gypsum is used in the manufacture of plaster. Porcelain is used in making bath-tubs, sinks and toilets. Bowls, cups and plates are also made from porcelain. Artificial bone joints and false teeth are made from porcelain.

               Some ceramics such as alumina and porcelain, do not conduct electricity and used as insulators in automobile spark plugs, electric power lines. Some types of capacitors are made from Barium titanate which is a ceramic material. Refractories are another important group of ceramic products used for lining furnaces. They resist heat and chemical action. Alumina, silica and magnesium compounds are used as refractories. Uranium oxide ceramics are used as fuel elements for nuclear reactors. Alumina in the form of ruby is used in the making of lasers, which produce extremely strong light beams.

 

               It is a matter of common experience that when a vessel is being filled up with water from a tap, the sound coming from it changes continuously. To begin with it is bass and gradually becomes shrill as the vessel gets filled up. Do you know why it is so?

               We know that the sound is a physiological sensation experienced when some vibrations are received by the ear. It is so produced by vibrating objects such as guitar strings, the column of air in an organ pipe or the membrane of a drum. Similarly when in a metallic vessel the water falls from a running tap, the metal starts vibrating and produces sound. Apart from the metallic sound, another sound comes from the metal; this sound is due to the vibrations of the air column above the water surface. This air column is formed between the water surface and the mouth of the vessel.

               As already explained the sound coming from the vessel is bass in the beginning and becomes shrill as the vessel gets filled up. This means that in the beginning sound has low frequency and later on high. The frequency of the sound produced depends upon the length of the air column. A longer air column produces sound of low frequency. As the vessel gets filled up with water, the length of air column becomes shorter and produces high frequency sharp sounds.

               As mentioned above the metal of the vessel also produces sound. These vibrations get suppressed as water fills in due to the decreasing air column. Materials with good sound absorbing properties are often fitted on walls and ceilings in buildings such as conference rooms, cinema or concert halls and public auditoriums in order to reduce or control sound levels.

               A musical instrument named ‘Jaltarang’ is based on the same principle and can produce a variety of musical notes. 

               It is our common practice to measure our body temperature with the help of a thermometer when we feel feverish. In ordinary thermometers, the lowest temperature is marked as 0°C. Today scientists can produce temperatures well below 0°C. Kelvin William Thomson a British Physicist first pioneered the absolute scale of temperature. The scale which is used to measure low temperatures therefore called ‘Kelvin’ scale or absolute scale of temperature.

               Theoretically the lowest possible temperature which a gas can attain is known as absolute zero. In centigrade scale it is equal to -273.15°C. This is based on the theory that the volume of a gas reduces in correspondence to the fall in temperature. So according to this theory, the gaseous volume would disappear and would loose all its kinetic energy if its temperature was lowered to -273.15°C or absolute zero. The gas molecules would be completely at rest, and it would not possess any heat. In practice, however, all gases change to liquids and then to solids before their temperature reach absolute zero.

               Scientists have never been able to reach absolute zero in their laboratory experiments. The lowest recorded temperature so far was achieved by magnetizing copper nuclei at a low temperature. When the electromagnet was switched off, the copper nuclei became demagnetized; the temperature fall was upto a million part of a degree above absolute zero.

               Materials react strangely when cooled to a temperature near absolute zero. At this temperature, oxygen gas freezes to a bluish white solid, and a rubber ball becomes so brittle that it shatters instead of bouncing. Mercury, normally a liquid, becomes and shines like hard silver. Hydrogen becomes a liquid and begins creeping into the sides of its container. Natural gas is shipped around the world in special containers after being cooled and liquefied at a low temperature.

               The Kelvin scale is used for scientific measurements, e.g. the liquefaction temperature on the Kelvin scale for Hydrogen is 20K and for liquid Helium it is 4.2K.

 

               When we look towards the surface of the moon with the naked eyes, we observe some dark smooth regions. The earliest astronomers believed that these dark regions on the moon’s surface were covered with water like the seas on earth. It was Galileo who first studied these dark areas through his telescope in 1609 and concluded that these were the areas covered with water. Galileo also studied some bright rugged regions of the moon’s surface and found that the bright areas were highlands. The highlands catch the sun’s rays. The darker patches are low lying plain areas of moon. Therefore once these were thought to be seas of the moon.

               In the later centuries, with the development of better telescopes, it became evident that the “Seas of the moon” were not seas at all, but low-lying and completely arid basins or plains. However, they continued to be called “Seas”. Astronomers called the dark areas Maria, meaning “Seas”. Strangely enough, no extensive Maria occurs on the lunar far side, which is almost entirely covered by mountainous terrae formations.

               The Seas of the moon can be divided into two types: the circular shaped and the ones with irregular outline. The circular type Seas are generally surrounded by mountains. Mare Imbrium (Sea of showers) and Mare Crisium (Sea of crises) on the near side and Mare Moscoviense (Sea of Moscow) on the far side are of this type. The irregular seas, such as Mare Tranquillitatis (Sea of Tranquillity) and Oceanus Procellarum (Ocean of Storms) have no extensive bordering mountain walls.

               The lunar seas are paved with successive lava flows. These might have been formed by the collisions of high velocity giant asteroids or meteorites. This would have ruptured the surface or triggered off volcanic eruptions allowing vast quantities of lava to well up from the lunar interior. The surface is made up of much the same elements as are volcanic rocks on earth but they contain no water. From the analysis of Maria basalts collected by the Apollo astronauts, it appears that the filling of the maria basins took place about 3500 million years ago. The terrae are much older regions than the maria. Most of these high ranges border the maria.

 

               We see a large number of stars in the sky every night. Since the ancient times they have helped man in more ways than one. He used to find out direction with the help of the Pole Star. He developed astronomy by studying stars and planets. Man has been trying to know more and more about these stars. Powerful telescopes have been made to provide valuable information about the stars. It is also possible to tell the date with the help of stars. Do you know how?

               To find out the date, take a large sheet of paper and draw a circle of at least eight inches in diameter. Divide this circle into twelve equal parts — just as a clock face is divided. On each division of the circle, write the name of each month. At the position of 12’O clock write the month of March. Keeping the usual order of the months, write them anticlockwise. Mark the centre of the circle as ‘North Star’. Imagine that the distance on the circle between each month is divided into 30 smaller divisions.

               Take your diagram outdoor on a clear night. Hold it in such a manner that the month of March is at the top. Imagine the diagram in the sky, with the North Star as the centre. Note the location of the Big Dipper. Now draw the Big Dipper on your diagram in the same location as you find it in the sky. Having done this, draw a straight line from the pointer to the North Star. This line will pass through the circle at a point that will indicate the date on which you are making your observation. If the line passes half way between the June and July positions on the circle, it is the day of 15th June. Of course, unless you have drawn a very large circle, it will be difficult to estimate 30 divisions between months on the circle. However, you can come within a few days of the exact date.

               The important thing is to note that on the diagram you have made on any particular date at midnight, the pointers are in line with that date on the star calendar. This is how we can find out the date by the stars.

               It is a matter of common experience that when we move into a dark place from a lighted one we are not able to see things clearly immediately. First they appear blurred and then gradually start appearing clearly. Do you know why it happens so?

               We see things in bright light as well as in dim light. The pupil of our eye adjusts its size according to the brightness of light. When we are in dim light the pupil expands to let more light enter the eye. When we are in bright light, the pupil contracts. But when we move into a dark room from bright sunlight, the pupil takes some time to dilate. Therefore it takes some time for things to become visible clearly.

               There is another important reason for this. The inner most layer inside our eye is called retina on which images of objects are formed. But we do not see the object until light-sensitive nerve endings on the retina send the brain a message along with the optic nerve. The coloured part of the eyes is called iris. This can open and close to let more or less light pass through the pupil. The retina is composed of many cells called rods and cones. These rods contain a purple-coloured substance called rhodopsin. When light coming from an object falls on the retina, it splits rhodopsin into two substances. The splitting of rhodopsin produces electrical signals which go to the brain and we see the object.

               If rhodopsin is continuously decomposed by the light entering our eyes, a time should come when the whole stock of rhodopsin would be decomposed. And in this condition the person would go blind. But actually this condition is never reached because it is simultaneously decomposed and formed. Therefore, the retina never suffers from a complete loss of rhodopsin. In bright light, our eyes may feel fatigued, but will never become blind.

               A lot of rhodopsin is decomposed in bright light. In this condition if we suddenly enter a dark room we cannot see things clearly because the amount of rhodopsin is reduced. It takes some time for the rhodopsin to form again, after which things become clearly visible to us.

               In the opposite case, when we suddenly enter into bright light from a dark room, our eyes get dazzled. The reason is that in a dark room very less rhodopsin gets decomposed. But on a sudden exposure in bright light a lot of rhodopsin gets washed. And thus, the intensity of the electric impulses reaching the brain increases and our eyes get dazzled.

               For the production of rhodopsin vitamin ‘A’ is required. Deficiency of vitamin ‘A’ causes night blindness. Vitamin ‘A’ is found in leafy vegetables, carrots, eggs and milk. 

 

               When milk is heated it comes up in the container and finally spills out. Do you know why does it happen?

               Unlike water, milk is not a simple substance. It is a colloid and contains many substances in suspended form. It contains fat, sugar, starch, protein, vitamins and minerals. When milk is heated slowly, the proteins and fat get separated. Since they are lighter than milk they get collected on the surface in the form of a layer called cream.

               During heating some water gets converted into water vapour. As the upper layer of the milk is covered with cream, the vapour gets trapped under it. As the milk is heated further the water vapour expands and thick foam is produced on top. Finally, the trapped vapour pushes the layer up and in the process bursts through. As the vapour escapes, a lot of cream and milk spill out. 

 

 

 

                It is very easy to prevent milk from spilling. All one has to do is to provide a passage for the vapour to go out. For this we can keep a long spoon in the milk container so that water vapour is able to escape along the handle of the spoon. This prevents the vapour from getting deposited under the layer of the cream and thus spilling out of the milk. 

               If we look at the history of mankind, we find many instances of great floods. The primitive man settled in the valleys that were close to rivers as it not only met his basic need for water but also made the land fertile after floods.

               Now, the question arises — what is flood? Generally, when a river overflows its banks and water spreads out over the surrounding lands, a flood is said to have taken place. Floods can be terribly destructive. They often wash away the fertile top soil and may leave the land unfit for cultivation for years to follow or take a large toll of human and animal lives.

               However, some floods are very useful to man. For example, the annual flooding of the Nile without which the great Egyptian civilization could not have existed. In fact, Egypt is called “The Gift of Nile”. From the beginning, the annual floods of the river were the basic mechanism of the economy and set the rhythm of life on river banks for the Egyptians.

               But, what causes floods? Sometimes rainfall is unusually heavy and the river banks may not be able to contain it. Water from other streams or reservoirs also feed the rivers. Erosion of soil around river banks due to wanton deforestation also causes flood. Combined with all these factors, the river overflows. We also know that most of the rivers build up their natural banks by depositing heavy particles on its sides as they can’t be carried away by the river flow. These natural banks are called “levees”. One of the main causes of flood is the breaking of the so called “levees” due to heavy pressure of water.

               There are several ways to control floods. One is to have levees or dikes to protect lowlands, where the river water tends to pile up. There must be some emergency channels, such as spillways or floodways to discharge out the excess water. Another method is to develop huge dams or reservoirs to hold back flood waters and release them in a regulated way. Another important method is the afforestations on the vicinity of river banks and embarkments to prevent soil erosion and also to make the river banks more compact. 

                We know that the sun is much bigger than the earth but appears very small because it is very far from our planet. The sun is about 150 million kilometres from the earth. When the sun is overhead its distance is 6000 kilometres less than the rising and the setting sun, which is equal to the diameter of the earth. The distance of 6000 kilometres is negligible as compared to 150 million kilometres and would not make any difference in the size of the solar disc. In case of any difference, the sun at noon would have been looked a bit bigger than that of the size of rising and setting sun. Do you know why do we observe exactly the opposite effect? 

 

 

               The bigger solar disc seen in the morning or in the evening is an optical illusion. If you take a photograph of the morning, noon and evening sun, then you will see that the solar image is of the same size. The optical illusion works for the lunar disc also, and because of this, the rising moon appears quite big.

               The reason for this optical illusion is probably because we tend to compare the size of the rising or the setting sun with earthly objects. When we see a tree, or a building or a ship near the solar disc then the size of the sun appears to be big. At noon, when the sun is overhead, we are not able to compare it with any close by object near the sun. In short, we can say that the bigger appearance of the rising and the setting sun is nothing but just an illusion. In fact, the sun’s size always remains the same.

               We all know that sea water is salty. It  contains many minerals which make it salty. Salinity of sea water varies a great deal in different parts of the ocean. On an average, there are 35 parts of salt to every 1000 parts of sea water. Now the question is whether it is possible to remove salt from the sea water and make it drinkable.

               There are several methods to make the sea water drinkable. One method is distillation. In this, sea water is boiled and the steam is condensed into water. Water gets vaporized leaving behind the salt. Water so obtained is fresh and good for drinking. For this purpose, nuclear energy or solar energy is used.

               In another method, electrical energy is used. Here, an electrical current is passed through the sea water. The electric current causes positive salt ions to flow in one direction and negative ions in the other. In fact, about 3.5 per cent of sea water consists of dissolved elements. These elements are sodium and chlorine which together form salt. On passing electricity, sodium ions move towards cathode and chlorine ions towards anode. This way, salt is removed from the water and water becomes worth drinking.

               In another method, some special types of membranes are used to purify water. There are thin membranes which let pure water through while blocking the flow of salts. Water filtered with these membranes becomes pure.

                By another method, the sea water is simply frozen. This process extracts salt from the water. After the salt has been separated from the ice, the ice is melted, giving fresh water. But this process is only for limited purposes.

               One of the best methods of obtaining fresh water is called multi-stage flash distillation. In it sea water vaporizes rapidly several times, each time in a higher vacuum and at a lower temperature.

               The world is now faced with an ever-increasing demand for fresh water.

               Scientists in many countries of the world are developing new methods for obtaining fresh water from the sea. In Israel, for example, and other oil-producing countries in Middle East, it has become worthwhile to build big plants to distill fresh water from the sea. However, due to high cost in processing, it is not still considered economically viable as an alternate source of fresh water. The research on the subject is still in experimental stage. 

               We know that there are nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. In terms of distance from the Sun, Mars is the fourth planet. It is the outermost of the terrestrial planets and is often called the Red Planet. Do you know why?

               We know that Mercury is the planet closest to the Sun. It rises and sets almost with the Sun. Therefore, we can see it either before sunrise or after sunset. Similarly, we see Venus either sometime before sunrise or sometime after sunset (dusk). But Mars can be seen clearly only for a month or two every other year. Among all the planets Mars is next only to Venus in brightness. Also it is very striking not because of its brightness but for its reddish-yellow colour. To study Mars, man has sent many space probes. These spaceships have provided us with many valuable facts about it. In 1976, the American space probes Viking I and II landed on the Martian surface. They gave valuable information about the atmosphere of Mars. It has been found that the atmosphere of Mars contains 1 to 2 percent argon, 2 to 3 percent nitrogen, 95 percent carbon-dioxide and 0.3 percent oxygen.

               The surface of Mars appears to be made up of bright and dark areas. About 70 percent of the Martian surface is found reddish and yellowish which gives the planet its characteristic colour. These areas constantly change shape. It has many rocks containing rusty iron and is covered with reddish-brown deserts. The winds blow at very high speeds of about 400 km/hr over Mars and create heavy storms in Martian deserts. The storms raise a lot of red dust in the atmosphere. Since Mars has a weak gravitational pull, these dust particles remain in the atmosphere for weeks together. And so Mars, because of its red dusty surface and the dust particles in the atmosphere, appears reddish orange to us.

               There is perhaps no human activity older, more varied or stranger, than fishing. He tricks and catches fish in different ways, such as using his bare hand, or fishing even with harpoon guns in whaling! But the method most used today is the one by which it produces the biggest share of commercial fishing known as trawling. Do you know how do trawlers fish?

               Trawlers fish with a bag-size net. It is let out on long warps or ropes. The fish are swept in at the wide, open end and then get trapped at the narrower, closed end. The trawler may be between 100 to 1500 metres long or more. In this system, the motorized fishing boats trawl by towing a large net in three different ways to keep the mouth of the net open. Firstly, a beam can be placed across the head of the net; secondly a pair of boats can be used - one at each side of the net to tow it and thirdly, some floating weights, called otter boards can be attached to the sides of the mouth of the net.

               However, the beam trawl is only used on a few small fishing crafts, and on the other hand, pair trawling is used to catch fishes from the bottom of the sea to enormous depths, sometimes at the range of 1500 metres or more. When the net is full, powered winches haul it on the board through a ramp. The otter trawl is widely used and is employed on almost every fishing technique except the smaller trawlers.

               The net gathers in everything including eggs, newly hatched fishes and algae. But this system is considered to be very destructive and alarming in the context of overfishing along the seas. Sometimes an entire fleet of fishing vessels is headed by a large factory ship fitted out just for processing of the catch. A single “sweep” of the net often taken in terms of tonnes of fish provides an idea of the quantity of fish caught in rich seas. Deep sea fishes like sardines and herrings together account for eighteen percent of the world’s catch.

               Today, the large motor fishing vessels are fitted with sonar or echo-sound equipments to locate a shoal of fish.

 

               You might say that the ball would fall behind the person who throws it because he would have moved forward with the moving train. But in fact this is not correct.

               You can perform a simple experiment to answer this question. You would be surprised to find that the ball lands right in your hand when thrown upward inside the moving train. Do you know why it happens so?

               In a moving train everything inside the train also moves with the speed of the train, for example, the fans, passengers, you and the ball in your hand. When you throw up the ball, a part of the speed of the train is imparted to it. It acquires a vertical motion in addition to its horizontal motion. The passengers in the train cannot see its horizontal motion but only its upward and downward movements.

               Imagine a man outside the train, who is watching your experiment. As we have said the ball possesses both vertical and horizontal motions, both these motions combined together make the ball travel along a parabolic path. The observer outside the train will see the ball moving in a parabolic path but a passenger in the train will see only the up and down motions of the ball.

               Now the question arises whether the ball follows the parabolic path or just moves up and down? Out of these two which one is right? In fact, all motion is relative to the observer. There is nothing like absolute motion and hence the motion of the ball is different for the two observers. 

               When you push the button of an electric door bell or calling bell it keeps on ringing as long as the button remains pressed.

               Do you know how does it function? An electric bell is a simple device based on the magnetic effects of electric current. It is used in offices, houses, industries and for fire alarms.

               It consists of a U-shaped electromagnet and a soft-iron armature. The armature has a small hammer for striking the gong. This hammer hits the gong repeatedly and produces sound. The gong is made of a metal. For operating the bell, a push button is pressed. In an electric bell, the button is a switch that connects the supply of electricity to the bell.

               When the button of the bell is pressed, the current flows through electromagnet winding, armature, contact spring and the contact screw. The flow of the current magnetizes the soft-iron core of the electromagnet. This attracts the armature, causing the attached hammer to strike the metal gong and thereby produce sound.

               As the armature moves forward due to magnetic attraction the contact spring moves away from the contact screw. This breaks the circuit and the current stops flowing. As a result, the soft-iron core loses its magnetism. It, therefore, no longer attracts the armature which, then, is pulled back by the contact spring to its original position. As soon as the armature comes to its original position the electric circuit is again completed and the soft iron becomes magnetized. It again attracts the armature and thereby the hammer strikes against the gong and produces sound. As long as the push button remains pressed, the circuit is alternately broken and completed causing the hammer to strike the gong. Thus an electric bell keeps ringing.

               If a steel core is used instead of a soft-iron, then the steel core will become a permanent magnet due to passage of electric current through the winding. Consequently, the armature will stay attracted even when the contact spring moves away from the contact screw, so the hammer will strike the gong only once.