Current Affairs 6th Class

Science in Everyday Life  
  • Science helps us to acquire knowledge about new things and happenings around us. Rapid development and improvement have come about through science and its various applications. Following are few a scientists with their remarkable discoveries:
Chief Scientists                                    Work   Nagarjuna                                                Indian mathematician; inventor of the digit zero Edward Jenner                                     Discovered numerous methods to cure diseases Edward Jenner                                     Discovered the world's first vaccine Alexander Fleming                             Discovered world's first antibiotic- penicillin—which cured various bacterial infections. Madame Curie                                      Discovered radium and polonium Antonie Van                                            Invented the microscope, an instrument, Leeuwenhoek                                       useful for studying various types of germs, examining the blood and so on. Louis Pasteur                                        Discovered methods of preserving milk, jam, etc., and pasteurization Jagadish Chandra Bose                 Studied the sensitivity of plants in detail  
  • Other Modern Scientists: Sir C. V. Raman, S Ramanujan, S. N. Bose, M. N. Saha, D.N. Wadia, B. Sahni, P. Maheshwari, G. N. Ramachandran, T.R. Sheshadri, Homi Bhabha and Vikram Sarabhai.

Things Around Us All the objects are made up of one or more materials. Materials may be classified in two categories: (1) Naturally occurring materials (2) Man made materials   NATURALLY OCCURRING MATERIALS · Examples are coal, wood, rocks, minerals, water, gold, petroleum, etc. MAN MADE MATERIALS · Examples are glass, plastic, fertiliser, paper, stainless steel, etc. · The entire universe is made up of matter. All materials and substances are made up of matter. Anything that we can see, touch, smell or taste is matter. · Anything that has mass and occupies space is called matter. · Matter can exist in three different states, i.e., solid, liquid and gaseous. (1) Solid - Example: wood (2) Liquid - Example: water (3) Gas - Example: oxygen · By changing the temperature, the state of the matter can be changed. Some forms of matter can be changed from one state to another and then can be reverted to the original state. · The process of changing a solid into a liquid by heating is called melting. The melting of a substance takes place at a fixed temperature. This temperature is called the melting point of that substance. · Ice melts at \[0{}^\circ C.\] Ice on melting forms water. On boiling water, forms steam. Steam is in a gaseous state. Most of the liquids keep on changing slowly into vapours at all temperatures. This process is called evaporation. · On continued heating, the temperature of a liquid rises and starts boiling at a fixed temperature. This temperature is called the boiling point of the liquid. Water boils at \[100{}^\circ C.\] · The process of changing vapour or a gas into a liquid by cooling is called condensation. For example, when water boils in a vessel, water droplets are formed due to cooling of steam on the lid and get converted into water. · The process of changing a liquid into a solid on cooling is called freezing, as water on cooling turns into ice. \
  • Gold, copper, iron and silver change into liquid and gaseous states at high temperatures.
  • Materials are classified based on their state, their solubility in water, their behaviour towards a magnet, their density with respect to water, their transparency or opaqueness, etc.
  • Things around us seem to be of an endless variety. Many objects and materials are made up of only a few basic units (building blocks). There are naturally occurring basic units on the Earth. These basic units are called elements. A few more elements have also been prepared by scientists. Now there are more than 110 known elements. These elements are said to be the building blocks of materials like the brick, which are the building blocks of a building.
  • Some of the common elements are hydrogen, helium, carbon, nitrogen, oxygen, sodium, magnesium, aluminium, silicon, phosphorus, sulphur, zinc, bromine, silver, tin, iodine, gold and mercury. Most of the common materials are made up of one or more than more...

Separation of Substances
  • A mixture refers to the physical combination of two or more substances in which their individual identities are retained. The components, whether two or more, can be separated. For example, separating small pieces of stone from wheat and rice, peeling off the skin of a banana before eating it, separating cream from milk, etc.
  • Separation of mixtures into their constituents is often necessary for several reasons. These are as follows:
  • To remove undesirable substances
  • To remove harmful substances
  • To obtain a pure sample of a substance
  • To obtain useful components
  METHODS OF SEPARATION
  • Winnowing: Winnowing is a simple method of cleaning food materials from a mixture. It separates the grains from the husk because one particle is lighter than the other. Farmers thresh wheat or paddy to loosen the grains from the chaff. This mixture is made to fall from a height. The breeze blows away the chaff, while the grains fall almost vertically. The chaff forms a separate heap at a little distance away from the heap of grains.
  • Hand picking: If the mixture comprises solids of different colours, shape or sizes, it can be separated by hand picking. For example, picking stone pebbles from rice, pulses, wheat or other food grains. This method is normally used when the quantity of impurities as well as the material to be cleaned is small in quantity.
  • Sieving: Sieving is possible only when the particles of a mixture are of different sizes. This method is used specially for purifying the mixtures of food materials from undesirable materials.
  • Separation with magnet: Magnets attract iron. Thus, good quality magnets are used to separate iron from a mixture.
  • Sedimentation and Decantation: Insoluble solids, i.e., solids that do not dissolve in a liquid can be separated from it by processes like sedimentation and decantation.
(a) Sedimentation is the process of settling down of an insoluble solid in a liquid at the bottom of a container. (b) Decantation is the process of separating out the clear liquid on the top without disturbing the sediment. This process is only done after sedimentation. For example, a mixture of sand and water is left for a while. The sand settles down and forms a layer at the bottom, this is sedimentation. And when clear water is poured into another vessel without disturbing the sand at the bottom, it is called decantation.
  • If a solid is soluble in water or two liquids are miscible (or soluble into each other) then, the process of sedimentation cannot be used for separation. Mixture of water and sugar and mixture of kerosene oil and petrol represent a solid soluble in water and two miscible liquids, respectively.
  • Two immiscible (or insoluble) liquids like a mixture of water and kerosene oil can be separated by decantation and by using a separating funnel. This method of separation is based on the property of the mixture that one constituent is heavier (water more...

Measurement
  • Measurement is one of the most useful processes in science and in our daily life. Without actual measurements, we cannot make correct judgments about a given object. It is not always easy to find out the length, area, volume or mass of different objects just by looking at them.
  • For the sake of uniformity, scientists all over the world have accepted certain standard units for measuring different quantities. For example
Quantity Standard Unit
Length Meter
Mass Kilogram
Time Second
  • Standard unit of length                                               : Metre
  • Meaning of length                                                          : Metre can be used as a unit to measure the length of a room, the height of a tree or a building or length and breadth of a playground.
  • Short form of standard unit                                      : m
  • Other standard units                                                    : 10 millimeters (mm) = 1 centimeter (cm)
                                                                                                            : 100 cm = 1 meter (m)                                                                                                             : 1000 m = 1 Kilometer (Km)
  • Standard unit of area                                                    : \[Metr{{e}^{2}}\]
  • Meaning of area                                                               : Area is the measure of surface of an object
  • Short form of standard unit                                      : \[{{m}^{2}}\]
  • Another unit of standard unit                                  : \[1\,acre=100\,{{m}^{2}}\]
                                                                                                              : \[1\,hectare=100\,acre=1000\,{{m}^{2}}\]
  • Standard unit of volume                                               : \[\begin{array}{*{35}{l}}
  • Metr{{e}^{3}}  \\
  • \end{array}\]or cubic meter
  • Meaning of volume                                                          : The space occupied by an object is called its volume. The space availablein a container is called its capacity. In fact, the capacity of a container is its inner volume.
  • Short form of standard unit                                        : \[{{m}^{3}}\]
  • Other standard units                                                       : When the object is small, instead of considering \[{{m}^{3}}\] as a unit, more...

Changes Around Us  
  • From morning till night, we observe many changes around us. For example, sudden change in the weather, rainfall, flowering of plants, germination of seeds, ripening of fruits, drying of clothes, change of day into night, melting of ice, evaporation of water, burning of fuels, cooking of rice, formation of curd from milk, rusting of iron, burning of fireworks, etc. Based on these examples, changes can be classified in the following ways:
(i)   Slow and fast changes (ii)   Desirable and undesirable changes (iii) Periodic and non-periodic changes (iv)  Reversible and irreversible changes (v) Physical and chemical changes   (i) Slow and fast changes: Slow changes take place over days, months or years. For example, rusting of iron nails, germination of seeds, ripening of fruits, etc. Fast changes occur within a short span of time. For example, spinning of a top, burning of a matchstick, curdling of milk by adding lemon juice, etc. (ii) Desirable and undesirable changes: The changes that are beneficial or desirable for us are called desirable changes. For example formation of curd from milk, formation of manure from cow dung and dead plants. But there are some changes that may be undesirable or harmful. These are called undesirable changes. For example-the burning of a factory, flooding of a river, rotting of food stuff, etc.
  • A change may be desirable at one time but undesirable at some other time. For example, the burning of a fuel (wood, coal) to produce heat is a desirable change. However burning is an undesirable change, when a house or a factory is burnt
  • A change may be desirable for someone and undesirable for others. The cutting of trees may be desirable for someone who needs wood but undesirable for others because it disturbs the balance in nature.
(iii) Periodic and non-periodic changes: Changes that occur again and again after a fixed interval of time and their recurrence can be predicted are called periodic changes. For example - winter, summer, autumn, spring and rainy seasons recur each year, the waxing and waning of the moon nights recur each month, generation of high and low tides in the sea, etc. Changes that do not repeat themselves at regular intervals of time and cannot be predicted are called nonperiodic changes. For example - train accidents, the occurrence of earthquakes, landslides, sneezing, etc. (iv) Reversible and irreversible changes: If a change can be reversed, it is called a reversible change. For example, ice changes into water on heating whereas on cooling water changes back to ice. Similarly, when we put a weight on a rubber band or a spring, it stretches; but when we remove the weight, it comes back to its original shape. If a change cannot be reversed, it is called irreversible change. For example, when coal is burnt, it changes into ash and smoke and we cannot get back coal from ash and smoke. Ageing, changing of milk into curd more...

Motion, Force, and Machines MOTION
  • When an object changes its position with time as compared to a stationary object, it is said to be in motion.
  • In science, motions are classified as follows: (i) linear motion, (ii) random motion, (iii) circular motion, (iv) oscillatory motion.
(i)Linear motion: A bullet fired from a rifle, a boy sliding down a slope or a ball rolling on the ground or moving along a line are examples of linear motion. Note: In a linear motion, an object may move along a straight line or a curved line. (ii) Random motion: The motion of a fly, of a player on a football ground, or of a child at home are not along a fixed path. They keep on changing directions. Such motions are called random motions. (iii) Circular motion: The Moon moves around the Earth. The Earth moves round the Sun. A bull moves around a central pole. These objects move along a circular path. Such motions are called circular motions. (iv) Oscillatory motion: If a hanging object is taken to one side and then released, it starts moving like a swing. Such to-and-fro motion is called oscillatory motion.   SPEED The speed of an object can be calculated by using the relation: \[speed=\frac{Total\,\,\text{distance}\,\,travelled}{Time\,\,taken}\] Example: If a train travels 120 km in 3 hours, its speed per hour will be \[Speed=\frac{120}{3}\] \[Speed=40\,Kilometre/hour\]
  • The standard unit of distance is metre and the standard unit of time is second. Therefore, the unit of speed is metre/second or m/s or \[m{{s}^{-1}}\].
  • For convenience, the speed of some objects is expressed in metres/minute. Cheetah is a fast animal. It can move at a speed of 1,700 metres/minute.
  FORCE
  • The push or pull applied on an object is called force. The direction in which the object is pushed or pulled is called the direction of force. The effect of force can bring three kinds of changes—
(i)   Change in speed (ii)   Change in direction (iii) Change in shape (i) Change in speed: If a force is applied in the direction of motion of the object, its speed increases and if the force is applied in the direction opposite to the direction of motion of the object, its speed decreases. For example: Hitting (applying force) a glass marble in motion with another marble from behind increases the speed of the moving marble. However, when the moving marble is hit (applied force) with another marble from the opposite direction, the speed of the moving marble decreases. (ii)Change in direction: Force can change the direction of motion of a moving object. For example: During a game of cricket, if a moving ball is hit by a bat, the direction of the ball changes; the smoke rising from an agarbatti changes its direction if we gently blow air on it. (iii) Change in shape: When a force is applied on an object, it may undergo a change in shape. more...

The Living World  
  • There is a variety of living organisms around us. Each one of them possesses a definite shape, size, structure and a colour pattern Similarly, things like living places (water and land), home (nests holes of trees), food habits, etc., give each organism a different identity.
  • Each kind of organism has many individuals. There are differences and similarities among the individuals of a kind based on which they can be recognised.
  • The individuals of a kind have a similarity in their body parts and their functioning. They eat the same kind of food and live in the same habitat. They cooperate among themselves for reproduction. Such a group of similar individuals is known as species. Each species has a name.
  • Each plant and animal has a scientific name consisting in two words. These scientific names help us in identifying each type of plant or animal and the group to which it belongs. When they are written the first letter of the first word (group name) is always written as a capital letter, but the first letter of the second word (individual name) is written as a small letter.
 
Example — Scientific names and their writing pattern
Indian Tiger Panthera tigris
Indian Peafowl Pavo cristatus
Man Homo Sapines
Mango Manifera indica
  Note: Although in different languages the plants and the animals may be called by different names, their scientific names are the same all over the world.
  • Living organisms are very different in shape, size, habitat, food habits and behaviour. They breathe in different ways and move around in different ways. They even have different ways of growing and reproducing themselves. All have different names but despite all these differences, they all have one most important thing in common—they are all living.
  • The living organisms share some features with the non-living objects. All living and non-living objects are made of matter. They all have mass and occupy space. But life is the process seen only in living objects in the form of growth, movement, feeding or eating, sensitivity, respiration, excretion and reproduction.
  • The world of living organisms can be divided into two groups:
(i) plants and (ii) animals.
  • An important difference between plants and animals is the way they obtain their food. Most animals, being able to move around, obtain food by looking for and going after it. However, most plants are fixed. They manufacture their own food. The process by which they manufacture their food is called photosynthesis.
  • Plants and animals reproduce themselves. They produce one or more individuals of their own kind. Plants reproduce mainly through seeds or spores. Certain plants reproduce through leaves, for example, Bryophyllum. Some also reproduce through stems, like ginger, potato. Animals reproduce by laying more...

Structures and Functions of the Living Body   All animals and plants have different organs to perform various functions. Each part of the body of an animal or plant is different in structure. The organs, however, function in coordination with one another.   SPECIFIC PARTS OF PLANTS
  • Plants have two main systems: (i) the root system (ii) the shoot system
  The Root System The root system grows mainly underground. Root systems are of two types: (i) Tap root system (ii) Fibrous root system (i) Tap root system: It is a main root and grows vertically down into the soil. The tap root gives out branches. For example, pea, neem, mango. (ii) Fibrous root system: Some plants do not have main root. They have many fibre-like roots. These are called fibrous roots. These roots spread out in the soil and give firm support to the plant. For example, wheat, grass, maize and millet. Advantages of the root system: As roots grow normally underground, they fix the plant to the ground. They absorb the mineral salts and water from the ground, which are needed for the plant to grow. Roots also help hold the soil together. They save the soil from being blown off or washed away.   The Shoot System The shoot system grows above the ground. It consists of the main stem, its branches and leaves. (i)   The stem: The stem holds the plant upright. The stem is the strongest part of a tree and is known as the trunk. Most trunks are observed with bark. The bark protects the inner part of the tree. The stems-of some plants are weak. They cannot stand erect. Stems carry water from the roots to the leaves and flowers. They also carry food from the leaves to other parts of the plant. They hold the leaves in such a way that the leaves get plenty of light from the sun. (ii) The leaves: Leaves are important parts of plants. They manufacture food for the plants. They are green because they contain a green pigment. This pigment is called chlorophyll. To manufacture food, the green leaves need sunlight, air and water. The process of making food in the presence of sunlight is called photosynthesis. (iii) Flowers and fruits: In a flower, the green leaf-like parts in the outermost circle are called sepals. Towards the centre of a flower many little stalks with swollen tops are present and they called stamens. The swollen tops are called anthers. They contain a powdery substance called pollen. The stamen is the male part of a flower. In the centre of the flower, there is a flesh-shaped organ called the carpel. The carpel is the female part of a flower. The little swollen portion at the base is called the ovary. The ovary contains egg-like structures called ovules. Pollen are transferred to the carpel in a process called pollination. This is done by insects, wind and water. Eventually, the ovules of the flower turn into more...

Air  
  • Air is everywhere around us. No living being can survive without air.
  • The air covers the whole Earth. This cover of air is called the atmosphere. We live within the atmosphere. It extends over hundreds of kilometres. Up to a height of 16 km, we find clouds, rain and snow. As we go up in the atmosphere, there is less and less air. Jet planes usually fly above the clouds.
  • Air is matter. It occupies space and has mass. It has no colour and we can see through it. It fills all the space available to it.
  • Air is a mixture of several gases. Nearly fourth-fifths (4/5) of it is nitrogen. About one-fifth (1/5) of it is oxygen. Air also has a small amount of carbon dioxide, argon, helium, water vapour and dust particles.
  • At higher altitudes, air is thin and under the water, the available oxygen is less. Thus, breathing becomes difficult. Therefore, mountaineers and divers carry cylinders containing oxygen with them. Oxygen is also supplied to the patients who suffer from breathing difficulties.
  • Oxygen is used by living organisms for respiration. During respiration, oxygen breaks down the food to release energy. During this process, carbon dioxide and water vapour are produced and released.
  • Carbon dioxide along with water is used by the green plants in the presence of sunlight to make their food. This process is called photosynthesis. During this process, oxygen is released. In nature, the balance of oxygen and carbon dioxide is, thus, maintained.
  AIR IS USEFUL TO HUMAN BEINGS
  • Air is required by human beings for respiration.
  • Air is necessary for burning. A chulha, sign or kerosene stove burn only when sufficient air is available.
  • Vehicles such as bicycles, few kinds of carts, scooters, cars, trucks and aeroplanes have tyres filled with compressed air. Such tires make transport smooth and easier.
  • Balls used for playing and balloons can be used only when they are inflated with air.
  • Compressed air is used in machines for digging, mining and breaking stones. It is also used for lifting liquid substances from a mine.
  • Compressed air is used in the brake systems of trains.
  • Air helps in drying agricultural products such as grains, pulses, dry fruits and wet clothes.
  • People feel cool in summer under a fan. The fan circulates air. This helps in rapid evaporation of sweat.
  • Air helps in the movement of sail boats, gliders, parachutes and aircraft. Birds, bats and insects fly in the air.
  • Air makes a windmill move. A windmill is used to draw water from tube wells and to operate flour mills. Along the coast, windmills are used to generate electricity.
   

Water   Water is the most common and important substance around us. Water is essential for almost every task we perform on a daily basis as well as for agriculture and industries.
  • All animals and plants need water. The human body has about 70 percent water by weight. Similarly the elephants and plants have 80 percent and 60 per cent water by weight respectively.
  • Animals drink water from ponds, streams and rivers. Plants take in water from the soil through their roots. From the roots, it goes to different parts of the plant. The plant uses this water for its life processes. It also loses water continuously from the tiny openings in the leaves. The process is called transpiration.
  • Seeds cannot germinate without water. Water helps animals in releasing heat which maintains their body temperatures.
  • A villager in India uses about 12 litres of water every day. In cities, a person uses 50-2000 litres of water every day. With the rising living standards, the requirement of water has also increased.
  • Large amounts of water are consumed in agricultural activities. Many industries such as paper, rayon, petroleum refining, fertiliser, dye, drug and chemical industries require large quantities of water.
  • In some countries, people use water to warm their houses. It is used to keep things cool. A car radiator is filled with water to keep the engine cool.
  • The largest amount of water on the Earth is in oceans. The oceans cover more than two-thirds (2/3) surface area of the Earth. Seawater is salty and cannot be used at home and in agriculture. So, we depend upon other sources of water like springs, rivers, lakes, ponds, wells, rain, snow and underground water. Water obtained from these sources is not always fit for drinking and cooking purposes. Many impurities and germs may be present in it.
  • Various methods are used to make this impure water fit for drinking. People in cities get pure water from taps. This impure water travels a long way to reach the taps. In many cases, water is first pumped from a source, such as a river or lake, and collected in a reservoir. Then it goes to the waterworks where it is cleaned. Here, it is filtered through layers of gravel and sand. The dirt stays behind in the sand, then water is treated with some chemicals like chlorine to kill the germs. The clean water is supplied through main pipes to different parts of the city. Smaller pipes take the water to each house.
At places where tap water is not available, people draw out water from rivers, lakes, springs and wells. Water from these sources should be made fit for use by boiling, filtering and treating it with some chemicals such as potassium permanganate.    
  • Pure water is colourless, odourless, tasteless and transparent. Small quantities of dissolved salts and gases give a pleasant taste to water. Water from the wells, more...


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