My Science School

          Iron is found everywhere on earth. It is not only present in the minerals but also in animals and plants. It is found even in the human body. Man began to use iron about 1200 B.C. after the Bronze Age.

          Five per cent of the earth’s crust is iron. It is estimated that the earth’s core contains huge quantities of iron and nickel. It is not found in a free state but occurs in a combined state with other elements. Its chief ores are: magnetite, haematite, limonite, siderite and iron pyrites. In India, these ores are mainly found in Bihar and Orissa. To obtain the iron from these ores, they are first finely ground with coal and limestone and then heated to a high temperature in a blast furnace. The melted iron comes out from the bottom of the furnace which, on cooling, becomes solid. The iron so obtained is called ‘pig iron’ and ‘cast iron’. It contains 5% of carbon. After reducing the percentage of carbon from 2 to 0.2% it is converted into steel. The process of the manufacture of steel from cast or pig iron is called “Bessemer Process”, named after Sir Henry Bessemer, who invented it in 1850.

          Iron and steel are very useful for us. They are used in all the industries in some form or the other. Appliances of our daily use such as knives, scissors, blades, locks, buckets, utensils are all made from iron. Ships, planes, trains, buses, cars, scooters etc. are also made from this useful metal. This is also used in the construction of bridges and buildings. Various kinds of nuts, bolts, pipes etc. are also made from iron.

          Stainless steel which is a very useful metal contains 18% chromium, 8% nickel apart from steel. In India, for making stainless steel, manganese is used instead of nickel because availability of nickel is rare in our country. Stainless steel has some special characteristics - chromium stops it from rusting and it is also not affected by acids and alkalies. Other steels are made with manganese, nickel and tungsten. Iron compounds are used to make pigments, inks and film for cameras. Iron oxide is used to make the tapes for tape recorders. 

          Everybody knows that in the city of Pisa in Italy, there is a beautiful tower that ‘leans’. Very few people know the reason of its leaning. Every year thousands of people go there to see this wonder. It is made of white marble. The walls are four metres thick at its base. It has eight storeys and is 55.4 metres high and measures 15.8 metres round the bases. There is a stairway which leads to the top and has 300 steps. From its top one can have a magnificent view of the city and the sea which is ten kilometres away.

          Now the question arises: what makes this tower lean and why does it not fall? Plumb line from the top is five metres away from the base, i.e. it leans over by five metres. If we drop a ball from its top, it would hit the ground five metres away from its base. It was intended as a bell-tower for the cathedral which is nearby. Its construction was started in 1174 A.D and completed in 1350 A.D. When the construction started nobody thought that it would lean, but it started leaning after the third storey was completed. The foundations of the tower were laid in sand and this may explain why it leans. Since the tower started leaning, the plans of its construction were modified and then the tower was completed. Since 1918, yearly measurements have been made. They show that the leaning is increasing. During the last one hundred years the tower has leaned another 30 cms. 

          But why does it not fall even while leaning? According to science, anything will remain stable as long as the vertical line drawn from its centre of gravity passes through its base. The centre of gravity is that point where the whole mass of the body is supposed to be concentrated. Till today the vertical line from the centre of gravity has been falling within the base of this tower. That is why it has not fallen. It is believed that when the tower leans further and the line from its centre of gravity pass out of its base, it will fall down. However, by using different new methods and techniques, Engineers and Technologists are now trying to arrest its further leaning.

 

          During the summer season, travellers in desert often get an impression of the presence of a pool of water at a distant place. But on reaching there they do not find a single drop of water. The desert deers also get the similar impression. They run here and there in search of this illusory water and finally die of thirst. A similar phenomenon is observed when we drive on a concrete road on a hot summer day. It is simply an optional illusion and is called mirage. Do you know how is it caused?

          The mirage is caused by total internal reflection of light. During the summer, the earth’s surface becomes very hot. These heats up the air in its vicinity but the upper layers of the atmosphere remain cool. Since hot air is always lighter than cold one, the air near the earth’s surface becomes lighter than the air of the upper layers. In scientific terms the refractive index of hot air is less than that of cold air. As such the refractive index goes on increasing as we go above the earth’s surface up to a certain height. 

          In such circumstances when the light rays coming from trees and plants enter from a medium of higher refractive index to a medium of lower refractive index, they get deviated from their path. This phenomenon is called refraction of light. As the rays travel more distance of varying refractive index the angle of refraction goes or increasing and a stage comes when it becomes more than 90°. At that stage the refracted light goes back into the medium from which it had started. This is called the total internal reflection of light. As a result of this reflection, the images of the trees and plants appear inverted, giving an impression as if these images have been formed in water. This gives rise to the illusion of the presence of a pool of water. This is what is known as a mirage.

         Sometimes another kind of illusion producing the opposite effect takes place. Over water, a layer of cold air may lie under a layer of warm air. This causes the light to bend downward. For example, a ship beyond the horizon may appear to be lifted into the sky. 

          Most people think that the water in the oceans is still. But it is not so. It is always moving in regular patterns. This movement of water is called ocean currents. There are many kinds of currents. One kind is a ‘stream’. A stream is a current with distinct boundaries. Another kind is a ‘drift’. A drift does not have distinct boundaries. Do you know how ocean currents are produced?

          There are three main reasons for the occurrence of the ocean currents. (1) The density of sea water varies from place to place, because the salt content is not same at different places. Water flows from the regions of higher density to regions of lower density thus producing currents. (2) Sun’s rays fall on the surface of the sea at different angles and as such produce unequal heating. This generates ‘convection currents’ in the sea. (3) Winds blowing on the sea surface push water into current.

          Currents are also caused by the rotation of the earth. Generally, the earth’s rotation produces clockwise currents in the northern hemisphere and counter clockwise currents in the southern hemisphere.

          Amongst these, the Gulf Stream is the most important. The water of this stream is blue and warm. This stream flows from the Gulf of Mexico north to Canada like a river in the middle of the Atlantic Ocean. London and Paris are less cold, because of this stream. It keeps ports in Norway free of ice all year. In addition to these, Brazil current, Japan Current North Equatorial current, North Pacific current etc., are the main ocean currents of the world.

          A cool current like the Labrador Current, which flows from the Arctic to the Atlantic, may carry icebergs into the trans-Atlantic shipping lanes. Ocean currents are important to the plants and animals in the oceans. The movement of water brings them food and nutrients. It also helps them during migration. Currents also affect the climate of the land. Ocean currents move water from warm to cold areas and vice versa.

          The collective name for a complex system of ocean currents flowing in the environs of the equator in Atlantic, Pacific and Indian Ocean is known as ‘Equatorial Current’. The pacific north equatorial current is the part of clock-wise ocean current system with Japan Current, North Pacific current and California current. Similarly in Atlantic, the North Equatorial Current is the part of the clockwise system with Gulf Stream, and Canaries current.

 

          The giant water waves which rise and fall periodically in the sea are called tides. Sometimes these tides are so high that they appear like high walls moving on the surface of the sea. Do you know what causes these tides?

          The main cause behind the formation of these tides in the sea is the force of attraction between the earth and the moon. We know that all the bodies in the universe attract one another with a force known as gravitational force. This force also acts between the earth and the moon. The moon is pulled towards the earth and the earth towards the moon. This force of gravitation acting between the earth and the moon is so strong that it can easily break a steel rod with a diameter of 400 kms. This force affects the solid part of the earth slightly but it causes rise and fall in the sea water noticeably.

           At any point in the sea, the water level keeps on rising for six hours and subsequently for next six hours it keeps on falling. This rise and fall of the water level is known as tide. The water level rises after every 12 hours 25 minutes. This means that during one day and one night, i.e., 24 hours and 50 minutes, every place in the sea experiences tides two times. Tides are formed both in the seas facing the moon as well as those on the other side. Since the moon comes to the opposite side of the earth after 12 hours and 25 minutes, tides are again formed on the same two spots.

          The force of attraction between the sun and the earth also affects the formation of tides but to a very small extent. When the sun, earth and moon come in a straight line, the earth experiences the maximum force of attraction. And the tide caused on such occasions is very large. It is known as the ‘spring tide’. The sea experiences such tides on the full moon and the new moon days. When the sun and moon are in a perpendicular direction, the earth experiences the minimum force of gravitation. The tide formed on such occasions is very small and is called the ‘neap tide’. Such tides occur between the full moon and the new moon days. Tides can be as high as 15 metres.

          Tides are useful in many ways. They bring many precious items of sea, on to the shore. The tidal power of the sea is also being used to generate electricity.  

          Bread is a popular food in almost all the countries of the world. Its ingredients vary from country to country. In most of the countries, however, bread is made from wheat or rye flour. In some other places it is also made from rice, barley, potatoes, peas and beans.

          According to the recorded history, the making of bread was started around 3000 B.C. in Egypt. Yeast was also discovered there only. Nowadays the common bread is made from dough prepared by kneading flour with water. A little yeast, sugar and salt are added to it. The yeast causes the dough to rise by forming bubbles of carbon dioxide gas in the dough. The dough is then formed into the shape of a loaf and baked in a loaf tin in the oven. In the process of baking the gaseous bubbles burst resulting in small pores inside the bread. It is mainly the yeast which gives the bread its taste and flavour. You can see these pores very easily in any bread piece.

          Cakes also have pores in them, but they are produced by the baking soda and not by the yeast. Baking soda, which is the mixture of tartaric acid and sodium bicarbonate, is used in the preparation of cakes. When this mixture is added to the dough and it is baked, carbon dioxide is produced. The bubbles of this gas burst on baking causing small pores. 

          Snow is formed of tiny crystals of frozen water that fall from the sky. Snow flakes have an infinite variety of shapes. They are usually hexagonal and may be flat, needle shaped or star shaped. No two snowflakes are exactly alike. Freshly fallen snow reflects about 95% of the sun’s heat back into the space. Do you know how snow fall takes place?

          Due to sun’s heat there is a continuous evaporation of water from the seas, rivers, lakes, ponds etc. Since water vapour is lighter than air, it goes up in the atmosphere and turns into cloud. We know that the temperature decreases as we go higher in the atmosphere. Since the capacity of air to hold water vapour decreases with the fall in its temperature at a certain height a large quantity of water vapour gets accumulated in the air. The air having excess of water vapours is said to be supersaturated. Under this condition the water vapours condense on the dust and smoke particles present in the air. On further cooling, they get converted into snow particles. These particles combine with each other to form crystals of snow. When the air cannot bear their weight, they fall down as snow flakes and go on accumulating on the mountains.

          Now the question arises: why does it snow on the mountains only? Why does it not fall in the plains too? In fact the possibility of snowfall at any place depends upon two factors - the altitude of the place above the sea-level and its distance from the equator. The higher the altitude of the place, the greater is the probability of snowfall there. Similarly the larger its distance from the equator, more are the chances of snowfall there. Even though the amount of snow formed in the atmosphere is very large, only a very small fraction of it falls down on the mountains in the form of snow. The remaining portion comes down as rains because while passing through hotter regions, it melts and turns into water. However, the temperature being low at the mountains, the snow does not melt into water there. It goes on piling up as snow and under the increasing weight of its accumulation layer after layer, it becomes harder and harder.

          Snowfall is very useful for us. When snow melts in summer, the melted water flows to rivers and is used for irrigation purposes. Fresh snow is very light and a good insulator, protecting the underlying plants from severe cold. Snow is a bad conductor of heat because of the air trapped between its particles. As such it acts as a blanket for the earth. In colder regions, people make houses of snow as it provides excellent protection against cold weather. In hilly areas, the roofs of the houses are made in a slanting shape, so that snow does not accumulate there. It saves the inhabitants from the adverse-effects of snow and also prevents the roofs from collapsing.

 

          Before the early part of the 20th century, the only known method of determining the depth of the sea at any point was by means of a cable. The ship stopped and a hemp line or wire with a weight at the end was lowered to the bottom. This was a slow, laborious task and not very accurate.

          Today man has developed innumerable instruments that help him to go deep into the seas and acquire more and more knowledge about their bottoms. Do you know how the depth of the sea is measured with the help of modern instruments?

          The equipment which is used to measure the depth of the sea is called a ‘fathometer’. It is installed on a ship. It produces sound waves having frequencies of more than 20,000 hertz. These are called ultrasonic waves. They cannot be heard by human ears. These waves are transmitted inside the sea. They are reflected back by the bottom of the sea. The reflected waves are received by a receiver and the total time taken by them to travel from the sea surface to the bottom and back to the surface is measured. Half of this time multiplied by the velocity of sound in sea water gives the depth of the sea at the point of the experiment. Thus the depth of the sea can be measured at any point. This technique is known as echo sounding or echo ranging. 

          This technique has been used to measure the depths of various seas and the deepest spot in each of the seas has been located using this technique. The Pacific Ocean is the deepest ocean. The average depth of this ocean is 4,282 metres (14,048 feet). The deepest spot in this ocean is located near Guam and has a depth of 10,668 metres (35,000 feet). Guam is an island in the Pacific Ocean. It is about 5,000 kms (300 miles) to the west of the Hawaii islands. A more recent survey located a spot with a depth of 10,924 metres (35,839 ft.) — as per a data obtained by Japan Maritime Safety Agency, using a narrow multi-beam echo sounder. Using depth as a criterion, the Indian Ocean occupies the second place. Its average depth is 3963 metres (13,002 feet). The Atlantic Ocean, coming third, has an average depth of 3926 metres (12,880 feet). Amongst the shallow seas, the Baltic Sea occupies the first place. Its average depth is 55 metres (1 80 feet).

            Studies of the oceanic crust have revealed that they are also as uneven as the surface of the earth. They are full of the skeletons of the aquatic animals as well as big and small sea plants. Volcanic ash is also found there.

          The most modern method of studying the oceanic crust is to use the laser beams. The laser beams are transmitted into the water of the ocean and the time taken by them from the surface to the bottom and back is measured. On multiplying the velocity of speed of light with this time, one gets twice the distance of the bottom of the sea. This method is very accurate. 

          A material that burns combines quickly with oxygen in the air. Burning, then, is a rapid process of oxidation. Most materials that burn are made up of mainly carbon and hydrogen. Combustion is another name for burning.

          In 17th century combustion was explained by other theory. Antoine Lavoisier, a French Chemist, discovered in 1774, that oxygen is essential for combustion. Some substances combine with oxygen extremely slowly. In that case no light and very little heat is produced. Rusting of iron is an example of such a slow oxidation.

          For a fuel to burn, certain conditions must be met. First, a substance that can burn must be present. Second, a good supply of oxygen must be present. Third, the fuel must be treated until it reaches its ignition temperature. The ignition temperature is also called the kindling point.

          Some substances like paper have low kindling points while other fuels like coal must be heated considerably before they can burn. Some substances like white phosphorus have a very low ignition point that is why it is kept under water.

          It would be almost impossible to count the number of ways in which fire is used. Fire provides light and cooks the food. Fire is used to heat water to make steam. Steam is used to run umpteen kinds of engines. Fire is used in industries for separating metals from their ores. Fire is also used in automobiles, boats and airplanes.

          When fire is under control it might be called man’s best friend. But once it gets out of control it is undoubtedly his worst enemy. Every year fires kill thousands of lives. It can destroy buildings and forests in large a proportion if it gets out of control.

 

          Whenever wood, coal or some other substance burns, smoke comes out. Smoke is produced due to the incomplete combustion of fuels. If complete combustion of fuels takes place, no smoke will be produced. In fact smoke is a colloid of solid particles in a gaseous form.

          Most of the fuels contain carbon, hydrogen, oxygen, nitrogen and small quantities of sulphur. When any fuel burns, we get carbon dioxide, water vapour, nitrogen and traces of sulphur dioxide. For the complete combustion of fuels a large quantity of oxygen is required because burning is a process of oxidation. Due to the lack of oxygen, fuels do not burn completely. As a result of this smoke is produced. Smoke mainly consists of carbon dioxide, water vapour and carbon particles. When the number of carbon particles present in the smoke is large, it appears gray or dark. These very carbon particles get deposited on the walls of the chimneys. This deposit is called soot.

          Smoke is the biggest pollutant of air and is very harmful from the health point of view. Today it has become a major problem in the cities. If it does not get scattered by wind, the atmosphere of the cities becomes highly foggy. Smoke is particularly harmful for the heart and lungs and is the cause of many diseases. It is also harmful to the eyes.

          However, in certain respects, smoke is useful also. It is used to protect the orchards from cold. In wars, smoke helps in camouflaging. It is also helpful in rain formation by enabling the water vapour to condense on its particles. 

          In the Southern Hemisphere, the Antarctic ice sheet overflows its land support to form shelves of ice on the sea; huge pieces, as much as 200 km. across, break off to form icebergs. In Northern Hemisphere icebergs are generally not over 150 metres across. However most icebergs are from some 20 glaciers on the west coast of Greenland. When glaciers, drifting from mountains and valleys, reach the sea, they got broken into big pieces by sea waves and tides. These big pieces of ice are called icebergs. However there are some glaciers which do not break even after floating for long distances in the sea and appear like mountains of ice.

          The sizes of the different icebergs vary. The smallest iceberg measures 5 to 6 metres in length and breadth but the bigger ones might be hundreds of metres long. Some icebergs with lengths and breadths of half a kilometre have been seen floating in the oceans. They float in sea water because ice is lighter than water. Their one-tenth part remains above water and the remaining under water. For example, if a 50 metre high iceberg is seen above water, then 450 metres of it will be under water. These icebergs contain huge quantities of snow. Some of them may contain 200,000,000 tons of ice. As an iceberg floats, some of the ice melts and pieces break off. Eventually, it completely disappears.

          Because of their huge weight and volume, the icebergs do not move in the sea on their own. They are pushed ahead by the sea waves. They are very dangerous for ships. A collision with them can cause a ship wreck. Though they can be detected with the help of modern instruments, yet mishaps do take place occasionally. On 14th April 1912, a ship named Titanic was broken to pieces when it collided with an iceberg. This ship was sailing to New York; 1513 passengers, who were aboard this ship lost their lives.

          A similar accident took place on January 30, 1959 when the ship Hans Hedtoft collided with an iceberg in southern Greenland and was wrecked. Now the United States and other countries have formed an International Ice Patrol. The patrol uses ships, planes and radars to locate icebergs.

 

          On the full moon day, the moon appears like a shining disc but it goes on waning till it disappears on the new moon night. And then it again starts increasing in size and becomes a full bright disc, on the full moon day. Changes in the moon’s size are called the ‘phases’ of the moon. Do you know why it occurs? 

          The fact is that the moon neither increases nor decreases in size. Its size simply appears to be changing because it changes its position with respect to the sun. We all know that the moon is the only satellite of the earth and revolves round the earth. It travels around the earth about 384,400 km away. This orbit takes 27 days and eight hours. It is illuminated by the sunlight. Only one side of the moon faces the earth. We do not see its other side. When the moon comes in between the earth and the sun, its bright side is not visible to people on the earth and only its dark side faces the earth. As a result the moon cannot be seen. This is the new moon day. As the position of the moon changes due to its motion from east to west with respect to earth, some illuminated part of its surface is visible to us. A week after the new moon, almost half of the illuminated lunar disc becomes visible to us. The bright part of the moon’s surface goes on increasing gradually and on the full moon day the whole disc, seen from the earth, is fully illuminated. On this day the earth is in between the sun and the moon. In the next fifteen days the bright portion of the lunar surface goes on decreasing and on the fifteenth day it disappears completely. In short, the changes in the apparent shape of the moon depend upon how much of its illuminated surface is visible to us.

          The cycle continues like this and we see the different phases of the moon. On the full moon day it appears just after the sunset and disappears only at the sunrise. The time between new moon phases is called the synodic month.

 

          We know that air is the mixture of oxygen, nitrogen, carbon dioxide, water vapour and dust particles. Air in motion is called the wind. Do you know how the wind blows?

          When any place on the earth gets heated by the sun’s rays, the air of that place also gets heated. Due to this heating the air expands and hence its density decreases or it becomes lighter. The hot air, due to this lightness, goes up in the atmosphere. And this causes a decrease in atmospheric pressure in that area. Under such a condition air from high pressure cold regions rushes to that place to create an equilibrium. This movement of air is called the blowing of wind.

          In the areas adjoining the sea, the earth becomes hot during the day. Due to this air becomes lighter and goes up in the atmosphere. To restore balance, cold air from the sea blows towards the land. During the night, a reverse movement takes place, that is, the earth becomes colder than the sea water and as such the air moves from the land towards the sea.

          It is very hot in the regions surrounding the equator. It creates an equatorial belt of low pressure. So there is a constant upward movement of hot air from these regions. This hot air flows out to the north and south.

          The rotation of the earth in its axis considerably affects the directions of the winds. The westerly winds are the direct result of the earth’s rotation from the west to the east. The spinning of the earth makes all in the northern hemisphere deflect towards the right and in the southern hemisphere, towards the left. Superimposed on the general wind systems are local winds. These are caused by temperature differentials associated with topographical features such as mountains and coastal belts. The presence of mountains also influences the wind direction. The mountains obstruct the winds and change their directions. The speed and direction of wind is measured by an instrument called an anemometer.

 

          Our body is like a furnace. The food we eat acts like fuel inside the body. It produces heat energy by the process of oxidation. Through this process about 2500 calories of heat is produced every day which can boil 25 kgs of water at 0°C. But what happens to this heat in the body?

          In our body certain metabolic activities are constantly taking place which do not normally allow the temperature to go beyond 98.4° F. Perspiration is one of the means through which the body furnace keeps its temperature normal. In fact, the body temperature is controlled by the ‘temperature centre’ located in the brain. This centre has three parts: control centre, heating centre and cooling centre.

          If the temperature of the blood falls below the normal due to some reason, the heating centre starts operating immediately. At the same time some special glands produce certain combustible chemicals which are used by our muscles and liver to raise the internal temperature of the body to the normal degree.

          On the other hand if the body temperature rises for some reasons the cooling centre goes to work. The process of oxidation slows down. Sweat glands start excreting sweat. Water, urea and some salts come out with the sweat. The sweat glands work fast only when the internal temperature of the body goes up. Sweat evaporates with the help of the body heat and this produces a cooling effect in the body. This process is similar to that of cooling of water in a pitcher during summer. Evaporation always causes cooling. Sweat, therefore, is a very effective process of controlling the body temperature. It also cleanses the internal parts. Many substances, harmful to the body, are excreted out through the millions of pores of the skin in the form of sweat. When the humidity is high, sweating causes uneasiness because the rate of evaporation under humid conditions decreases.

          Generally the voice of women is sweeter than men. Even boys have feminine voice till the age of eleven or twelve years. But later it starts becoming deeper. Voice of girls, however, does not change much with age.

          Normally the age of eleven to thirteen years is known as the period of puberty. During this period some of our glands produce sex hormones. These hormones bring many changes in the bodies of boys and girls. In boys they are responsible for the growth and appearance of the hair under arms, auxiliary hair, pubic hair and facial hair. The voice of boys starts becoming deeper. Their bodies produce a hormone called ‘testosterone’ which is mainly responsible for changing the length and thickness of the vocal cords. This also affects the larynx. As a result a man’s larynx becomes larger than that of a woman. Man’s vocal cords are also longer than those of woman. Due to this the frequency or pitch of a man becomes lower than a woman’s and hence the male voice becomes deeper than that of a female.

          Though this hormone is not produced in the girls, yet a slight change takes place in their voice also. This change occurs mainly due to the further growth of their throat, mouth, nose and upper jaw.