My Science School

              Plastic surgery is a branch of surgery devoted to restoration, repair and correction of malformations of tissues. It concerns not only return to normal appearance but also the restoration of function. The field of plastic surgery has several sub-divisions such as cosmetic surgery, management of congenital defects, burns, wounds and other acquired defects.

             Cosmetic surgery deals with improving the appearance of tissues or organs such as the nose, face, eyes or breasts. The most common types of cosmetic surgery are face lift to remove wrinkles from the face and neck and a rhinoplasty to change the shape of the nose.

             Plastic surgeons treat physical defects that exist since birth (congenital defects) or are caused by injury or disease. Often the body part that is defective or damaged does not work as it should. In such cases, the surgeon does reconstructive plastic surgery. This often requires grafting. In grafting skin muscle, bone or cartilage is transplanted from a healthy part of the body to the hurt or damaged part. Sometimes reconstructive surgery involves reattaching several limbs, rebuilding damaged tissues, restoring damaged blood vessels and nerves. Plastic surgeons are available almost in all the hospitals.

             Plastic surgery has been practiced for hundreds of years in China and India. Chinese and Indian doctors were reshaping noses and lips long ago.

 

            Plastics do not occur naturally but are manufactured. The word ‘plastic’ has originated from the Greek word ‘Plastikos’ which means ‘to mould’. It is made from simple organic chemicals. It has many varieties and colours.

            Plastic was invented by Alexander Parkes of England in 1862. In those days it was called ‘Parkesine’ after him. Parkesine was the first plastic ever produced.

            Many plastics have ‘poly’ in their names for example, polythene. Poly comes from a Greek word meaning ‘many’. Polythene means ‘many molecules of ethene joined together’.

                   The manufacturing of plastic on a commercial scale was started for the first time by Leo Hendirk Backeland. He made it from phenol and formaldehyde. Subsequently, new techniques were developed for the production of plastics. Today, scientists have discovered many raw materials which are used in the making of various kinds of plastic products. Most plastics are made from chemicals found in oil, although a few come from wood, coal and natural gas. Common types include polythene, polystyrene, PVC and nylon.

                  Today, plastic has become an integral part of our life. Its uses are endless. Transparent plastics are used for making lenses and windows of aeroplanes. Polythene bags, a plastic product, are used in almost all walks of life. Articles of domestic use like buckets, cups, brushes, combs, baskets, cabinets for radios, transistors etc. are also made of plastics. Toys and sports goods made from plastic have flooded the markets everywhere. The yarn for making Terylene cloth is, in fact, made from plastic. Today scientists have even succeeded in developing heat insulating plastics. Foam cushions, seats in trains, cars and aeroplanes - all are made from plastics. Now, plastics are used as surgical aids also. There is hardly any field of life in which plastics are not used. 

Ice, which we generally see around us, is made by freezing the water. Water turns into ice when it is cooled to 0°C. There is another kind of ice which is known as dry ice.

Dry ice is solid carbon-dioxide. It is formed when carbon-dioxide turns directly from a gas into a solid at a temperature of about - 80°C. It is so cold that if held in hand it causes frost bite. It is usually prepared by cooling carbon-dioxide under high pressure. It looks rather like snow but can be made into blocks by compressing the flakes. Dry ice is very heavy.

Dry ice is very important for cooling or refrigerating foods such as ice creams and meat and medicines. It is also used to stimulate fog and steam effects in television or stage plays because it rapidly turns back to gas at ordinary temperature without becoming liquid.

 

             Warm clothes that we wear during the winter are mostly made of wool which comes from sheep. Wool is also obtained from goats and other animals like llama and alpaca. Mostly it is the wool from sheep that we use for our winter dresses. Wool is basically fine soft hair that forms the coats of these above mentioned animals. Hair grows on the body of sheep, as they grow on our heads. Sheep and similar other animals have fine thick wool hair which are called fleece. The fleece or hair of a sheep insulates it from the cold in winter. In other words, wool is animal fibre forming the protective covering or fleece of sheep. Do you know how this wool comes to you from sheep? Wool is mainly obtained by shearing fleece from living animals and sometimes from slaughtered sheep also.

              When the fleece is sheared, it is rolled up in bundles sorted out into different qualities or grades, cleaned; stains of various types, dried, entangled fibres are disentangled, twisted and spun in soft, loose irregular thread or yarn. Such strands used together are called 2-ply, 3-ply etc., according to the coarseness or fineness of fabric desired. Wool may be dyed at the various stages of the manufacturing process. Wool fibre is warmer but coarser than cotton, linen, silk and rayon.

 

Continue reading "How do we get Wool from Sheep? "

              Copper is a reddish orange metal that has been used for more than 5000 years. After gold it was the first metal to be discovered by man. Native copper is found in small quantities in solid or granular form. Most of it occurs in the combined state as sulphides, carbonates, silicates and oxides. Copper pyrite is its most important ore. About 50% of world’s supply of copper comes from copper pyrite.

                     History reveals that copper was used by man as early as the Stone Age. By 4000 B.C. mining of copper had begun, by 6000 B.C. man had started using instruments, weapons and ornaments of copper. Later, man came to know that bronze, an alloy of Cu, Zn and Sn is harder than Cu. He then used bronze for making utensils, weapons and ornaments. Other alloys of copper like brass are also used for the same purposes. Copper also makes an alloy with aluminium which is called aluminium bronze. As time passed copper came to be one of the most important metals in the world, used extensively in electrical and other industries for making wires, dynamo, coils, motor coils, for minting purposes, to make coins, in engineering industry and so on. Copper is used all over the world for making electric wires because of its softness and tenacity. It is a very good conductor of electricity and heat. Much of the world’s copper comes from Canada, USA, Chile, Zambia and Russia. 

Most of the gases can be prepared in the laboratory but there are some which are found in nature only. Helium is one such gas.

                It is an inert gas. It is odourless and tasteless. Helium has some special characteristics due to which it has proved very useful for us. It is second lightest gas next to hydrogen but it has a speciality that, unlike hydrogen, it is non inflammable.

               This gas was discovered in 1868 independently by English scientists Sir Joseph Norman Lockyer and French Chemist, Pierre Janssen. While studying the solar spectrum to find the elements present in the sun, they came across some lines which were not observed earlier. These lines suggested the presence of a new element in the sun. The element was named as Helium after the Greek word ‘helios’ meaning ‘the sun’. Thereafter, scientists made efforts to know if helium was present in the earth’s atmosphere. They detected very small quantities of helium in the atmosphere. Atmospheric air contains only one part in 1, 86,000 parts, i.e., 0.0005239 percent.

               On account of its lightness and non-inflammability, it is used in weather balloons. Helium is also used to ease the breathing difficulties of asthmatic patients. Deep sea divers are given a mixture of oxygen and helium for breathing so that after coming back, they do not suffer with bends. Helium is also used to weld aluminium. A mixture of helium and neon is used to produce laser beams. Helium can be liquefied at - 268.9 degree centigrade. Liquid helium is used in low temperature work.

               There are some places in America like Texas, New Mexico, and Kansas etc. where the amount of helium present in the atmosphere goes upto 8%. It is also present in atmosphere in Canada, Africa and the Sahara desert. America is the world’s richest source of this gas and is therefore the biggest seller of helium to other countries. In earlier times this gas was very costly, but now it has become quite cheaper.

                 Without oxygen there would have been no life on this earth. Without it no living being - trees, plants or animals can survive. Hence it will not be a misnomer to call it a life-giver. Do you know what is it and why is it absolutely essential for us?

                Oxygen is a gaseous element. This was discovered by two scientists independently. Carl Scheele, a Swedish chemist, discovered oxygen in 1772 and Joseph Priestley, discovered it in 1774 in England. It is a colourless, tasteless and odourless gas. In the atmosphere the air contains 21% oxygen, 78% nitrogen and rest one percent other gases. In the earth’s crust, it is found in the form of oxides of metals, the proportion being up to 50%. At - 182.9°C under right pressure it can be liquefied. In the liquid state its colour becomes light blue. At - 218.4°C, it can be converted into solid state.

               In the laboratory, this is obtained by heating the mixture of potassium chlorate and manganese dioxide. From the atmosphere, it is obtained by the fractional distillation of air. The air is compressed to two hundred times the normal atmospheric pressure and passed through a narrow hole into a chamber. As the pressure is suddenly dropped, the air is liquefied and collected in the chamber. The nitrogen gas is separated from this by a special method and oxygen is obtained in the liquid state.

              All living beings need oxygen for breathing. Plants also ‘breathe’ oxygen. They absorb oxygen during the night. During the day they give off oxygen by photosynthesis.

              By burning oxygen gas along with the acetylene gas, a high temperature flame is produced. This flame is used for welding and cutting metals. Liquid oxygen is also used as a fuel in space vehicles.

 

Continue reading "How is oxygen useful to us? "

                 It is commonly observed during the rainy season that water falling on roads and streets disappears after a few hours. Similarly, in summer, wet clothes dry up very soon. Do you know where this water goes? This water gets converted into vapour and goes into the atmosphere. Conversion of water into vapour is called evaporation.

                 How does evaporation take place? Every substance is made up of very small particles called molecules. These molecules are held together by strong forces of attraction called cohesive forces. These forces are opposed by the repulsive forces caused due to the motion of molecules. As long as the cohesive forces are far greater than the repulsive forces, the substance remains in the solid state. When the substance is heated up, it absorbs heat energy due to which the molecules are set in rapid motion. This motion starts counterbalancing the cohesive force, that is, this force tries to separate them apart. When the repulsive force generated by the motion of molecules equals the cohesive force, matter changes from solid to liquid state. If the liquid is continued to be heated, the molecules move still faster and when the force due to the increased motion exceeds the cohesive force, the molecules of the liquid become free and escape into the air. This is how liquid is converted into vapour. The liberation of the molecules from the liquid surface into the air is called evaporation. Evaporation takes place at all temperatures.

              This explains the drying up of clothes in the air. The rate of evaporation increases with the rise in temperature. Wet clothes put in the sun dry up faster than in shade because at higher temperature the motion of molecules becomes faster and the evaporation is also faster. It also takes place more rapidly when the air is dry. That is why clothes dry up more quickly on a dry sunny day than on a damp cloudy day.

Silicon is a non-metallic element. It is not found in nature in a pure form. Pure Silicon is a hard, dark grey coloured material. It shines like metals and is crystalline in nature. At ordinary temperature, it does not react with other elements, but at higher temperature it makes compounds with other elements.

              The earth’s crust has 28% Silicon whereas china clay contains 50% Silicon. It is also found in rocks, sand, water, bones, etc. Sand has a large quantity of Silicon.

              Silicon is extracted from the compound Silicon dioxide. When Silicon dioxide is heated in an electric furnace, oxygen is removed and Silicon is separated from Silicon dioxide.

             Most of Silicon is found in the form of Silica which is another name of Silicon dioxide, a compound of Silicon and Oxygen. Quartz, jasper, milky stone and sand - all are different forms of Silica. Silicate is another compound of Silica. Mica and asbestos are well known forms of Silicates.

            Silicates are very useful to us. They are used in making many different kinds of glasses, enamels, china clay, etc. Sodium Silicate is used in the making of soaps, prevention of the rotting of wood and eggs and in dyeing. It is also used for smoothening and for making artificial rubber.

            Chief use of Silicon in its pure form is in making photocells, transistors and Silicon chips containing micro circuits for computers and other electronic components. A compound of Silicon and carbon called Silicon carbide or carborundum is used for polishing metals. By mixing Silicon in steel, its utility is enhanced. Silicon is also used for making semiconductors which have proved very useful in our life. Silicon mixed with sand and earth is used for making bricks.

 

             An object is said to be hot if its temperature is more than our body temperature. If we touch such an object, heat flows from it to our body and we feel its sensation. Similarly, an object is said to be cold if its temperature is lower than our body temperature. When we touch it, heat flows from our body into that object. Do you know why it happens?

            We know that our body is made up of cells. And consequently these cells are made up of molecules. At normal body temperature these molecules are in motion. When a hot substance touches a part of our body, the fast moving molecules of that substance accelerate the motion of the molecules of the cells of the affected part of our body. And when the molecules of cells of that part stand the fast vibrations, the cells start breaking up. It is the breaking up of the cells that give the burning sensation. To repair the damaged cells, blood circulation becomes faster in the affected area. That is why the affected part becomes red.

 

Continue reading "Why do hot things burn us? "

                 You might have seen small drops of water on grass, plants and trees shining like pearls in the early hours of morning. These water-drops are called dew. Quite often people think that dew drops, like rain-water, fall on the earth from sky during night but this is not true.

                  Dew drops are formed due to condensation of water vapours. Air around us contains water vapours which we call moisture or humidity. Hot air contains more moisture as compared to cold air. During the night when the hot air comes into contact with some cold surface, water vapour present in it condenses on the cold surface in the form od froplets. These tiny drops of water are called dew drops. The process of dew formation can be seen in a simple experiment. Take a tumbler and place it on a table. Now put some ice or ice-cooled water inside the tumbler. You will notice that after some time on the outer surface of the tumbler small drops of water have appeared. These water drops are formed by the condensation of the water vapours present in the air. Exactly in the same way when the trees, plants and grass become cold during night, the water vapours of the air condense on them in the form dew.

                  The dew formation is more when the sky is clear and less when it is cloudy. When the sky is clear and the trees and plants are cooler at nights, there is more evaporation of water and hence more dew formation. But when it is cloudy, trees and plants do not get cool in the night and hence there is less dew formation. As the sun raises high in the sky, these dew drops evaporate into air. 

              Every substance is made up of very tiny particles called molecules. A molecule is the smallest part of matter that can exist independently and exhibits all the properties of that substance. For example, if we take a molecule of sugar, it will exhibit all the properties of sugar such as taste, shape, colour etc. Molecules of different substances differ in size. Some are only few billionths of a centimetre in size while some other molecules are thousand times larger. Molecules of gases are small in size. One cubic centimetre of air contains about (25,000, 000, 000, 000, 000, 000) molecules.

             Even though a tiny piece of matter contains a very large number of molecules, there are empty spaces in between them. Molecules of matter are constantly in random motion. As the temperature increases, the motion of the molecules also increases. The hotter the substance, the faster is the motion of the molecules. Molecules of a gas move very fast in comparison to the molecules of liquids and solids. Even the molecules of ice are in motion. Isn’t it surprising then that though molecules of all substances are in motion, substances don’t appear shaky? Why? The reason is that there exists between the molecules a force of attraction which keeps them together. If this force is not present, the molecules of matter will scatter away in all directions.

             When the molecules of a solid are heated, their speed increases and the force of attraction between them decreases. If we continue adding heat, the speed of the molecules would be still faster and the solid will change into the liquid state and, finally, to the gaseous state. 

 

From the very ancient times man has a deep fascination for this shiny yellow coloured metal which symbolizes affluence. The statues and temples of our gods and goddesses are decorated with gold ornaments. Kings and Emperors always gave great importance to gold. Man has always shown a great affinity for it. What is so special about gold that it has always been costly and tends to become costlier?

             The increasing preciousness of a substance depends on many factors. First is its rare availability. Second factor is its utility, third is its beauty and fourth is the least reactivity with air and water. Gold is an element that possesses all the four qualities. It is a rare metal found in very small quantities. Its colour and shine are very attractive. It is not affected by heat, cold, wind and humidity. No wonder, it is a costly metal.

            Gold is a shining metal of yellow colour, found in nature in very small quantity. It is found in both free and combined states. To extract gold from its ores is a costly process. An exception was a small rock of seventy and a half kilogram found in Victoria, Australia which yielded seventy kilograms of pure gold. But such rocks are rare. Extremely small quantity of gold is obtained from gold mines. It is traceable in sea water also, but its extraction from sea is uneconomical. It also occurs as a fine grain is sand and gravel.

 

Continue reading "Why is gold so costly? "

          It is a general belief that dust is very harmful to us. But this is only one side of the picture. Dust also is very useful to us. Before we go through the uses of dust, it is essential to know what dust is and how it is formed.

          Every solid substance is composed of very small particles. When these small particles of matter are scattered, they become dust particles. For example, if we break a brick or a stone into small pieces, it will turn into small particles of dust. There are different ways by which dust is formed. When solids break, dust is formed. Smoke generated by the burning of coal, wood, petrol etc, also produces dust. Dust particles also come from dead plant and animal matter, sea salt, desert, volcanic ash etc. These particles get mixed with air and are called dust particles. Air carries dust particles from one place to another. The particles of the earth’s surface also fly in the air in the form of dust.

          The biggest utility of dust particles is that they help in the formation of rains. The water-vapour in the clouds condenses on dust particles in the form of water-drops. These drops fall on to the earth as rains. The absence of dust particles can delay the rain. Likewise, mist, fog etc. are also formed due to the presence of dust particles in the atmosphere.

          The dust particles present in the atmosphere scatter sun-rays in all directions. Due to this scattering, there is not complete darkness for one to two hours even after the sun set. The appearance of red colour at the sunrise and the sunset is due to dust particles and water vapour. The beautiful rays of the sun seen in the twilight are also due to these dust particles. Thus we see that dust particles which are regarded as absolutely harmful by people are in reality very useful.

          It is a matter of common experience that ice floats on water. Howsoever large the size of ice may be it will not sink. Even icebergs which are huge masses of ice keep on floating in the sea. Do you know why ice floats on water?

          The law of floatation of bodies was given by the Greek scientist Archimedes. According to this law, whenever a body is placed in water, it is acted upon by two forces - the weight of the body acting downwards and the buoyant force of water acting upwards. If the weight of the body is equal to or less than the up thrust of water, the body floats on water. In other words, if the weight of the body is equal to or less than the weight of the water displaced by it, it will float on water. On the other hand, if the weight of the body is more than the weight of the water displaced, the body will sink in water. Hence a body floats when its weight is equal to the weight of the water displaced. A piece of wood floats on water because its weight is less than the weight of the water displaced by it. Since the weight of wood is nearly half of the weight of an equal volume of water, half of wood is under water, while the other half is above it. Similarly, the weight of cork is nearly one-fifth of the weight of the water displaced by it, so approximately one-fifth of cork is under water while the rest remains above water. You can understand the floatation of ice also on the basis of this law.

          In general, when a liquid changes to solid, it contracts because its molecules come closer to each other. As a result of this, the volume of the substance decreases or its density increases. Hence a substance becomes heavier in solid state than in the liquid state.

          But water is a peculiar liquid. When it becomes ice, instead of contracting, it expands. The volume of ice becomes more than that of the water. The effect of the increase in the volume of ice is that its density becomes nine-tenth of water, that is, ice becomes lighter than water. So we get about 10 litres of ice made out of 9 litres of water. And as you know, ‘litre’ is a measure of volume. That is why nearly nine-tenth of ice is submerged in water, while only one-tenth is above water. The ice under water (9/10 of the whole) displaces water whose weight equals that of the whole ice. This law of floatation is derived from Archimedes principle. This also explains how the maximum portion of the giant icebergs remains sub-merged in water while only a tip (1/10 part) is above water.

          Bursting of water pipes in cold regions is due to the volume of ice being greater than that of water. As soon as water freezes, the volume is increased which produces strong force due to which pipes burst? In Finland, this property is utilized in breaking rocks. Water is filled in empty spaces available between rocks. When water freezes, it expands and generates enough pressure to cause cracks in the rocks.