Properties of Whole Numbers

Properties of Whole Numbers A whole number added to 0 remains unchanged.

A whole number added to 0 remains unchanged. Thus, 0 is called the additive identity in whole numbers.  The product of two whole numbers is the same, no matter in which order they are multiplied. This is called the commutative property of multiplication.  A whole number multiplied by 1 remains unchanged. Thus, 1 is called the multiplicative identity in whole numbers.  Whole numbers are closed under addition and multiplication.  Subtraction and division are not commutative in whole numbers. Whole numbers are not closed under subtraction and division.  While adding whole numbers, we can group the numbers in any order. This is called the associative property of addition.  While multiplying whole numbers, we can group them in any order. This is called the associative property of multiplication.  The sum of the products of a whole number with two other whole numbers is equal to the product of the whole number with the sum of the two other whole numbers. This is called the distributive property of multiplication over addition.

Whole Numbers

Whole Numbers The numbers used for counting are called natural numbers.

The numbers used for counting are called natural numbers.  The number that comes immediately before another number in counting is called its predecessor.  The number that comes immediately after another number in counting is called its successor.  To find the successor of any given natural number, just add 1 to the given number.  The value of nothing is represented by the number zero. 

 Eg: 3 – 3 = 0
Natural numbers together with the number zero are called whole numbers.  When comparing two whole numbers, the number that lies to the right on the number line is greater.  When comparing two whole numbers, the smaller number lies to the left on the number line.

Importance of Brackets

Importance of Brackets Brackets help in simplifying an expression that has more than one mathematical operation.

Using brackets: Brackets help in simplifying an expression that has more than one mathematical operation. If an expression that includes brackets is given, then turn everything inside the bracket into a single number, and then carry out the operation that lies outside. Eg: 1. (6 + 8) x 10 = 14 x 10 = 140 2. (8 + 3) (9 - 4) = 11 x 5 = 55 Expanding brackets: The use of brackets allows us to follow a certain procedure to expand the brackets systematically. For example: 8 x 109 = 8 x (100 + 9) = 8 x 100 + 8 x 9 = 800 + 72 = 872 105 x 108 = (100 + 5) x (100 + 8)

= (100+5)x100+(100+5)x8 =100 x 100 + 5 x 100 + 100 x 8 + 5 x 8 =10000 + 500+ 800 + 40 =1134

Roman Numerals

Roman Numerals Many years ago, Hindus and Arabs developed a number system called the Hindu–Arabic number system.

Hindu–Arabic number system: Many years ago, Hindus and Arabs developed a number system called the Hindu–Arabic number system.  It is the name given to the number system that we use today. Roman numerals: It is the numeral system that originated in ancient Rome.  This numeral system is based on certain letters, which are given values and are used as numerals.  The following are the seven number symbols used in the Roman numeral system, and their values:  I V X L C D M 1 5 10 50 100 500 1000 Seven letters of English alphabet, i.e. I, V, X, L, C, D and M, are used to represent Roman numerals.  Roman numerals do not have a symbol for zero.  Roman numerals are read from left to right, and are arranged from the largest to the smallest.  Multiplication, division and other complex operations were difficult to perform on Roman numerals.  So Arabic numerals were used.  The Roman numerals for the numbers 1 - 15 are shown below: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 I II III IV V VI VII VIII IX X XI XII XIII XIV XV We can find these roman numerals in some clocks. Rules for Roman numerals:

In Roman numerals, a symbol is not repeated more than thrice.   If a symbol is repeated, its value is added as many times as it occurs. For example, if the letter I is repeated thrice, then its value is three. The symbols V, L and D are never repeated. If a symbol of smaller value is written to the right of a symbol of greater value, then its value gets added to the symbol of greater value.   For example, in case of VI, I is written to the right of V.  It means that 1 should be added to 5.  Hence, its value is 6.If a symbol of smaller value is written to the left of a symbol of greater value, then its value is subtracted from the symbol of greater value. For example, in case of IV, I is written to the left of V.  It means that 1 should be subtracted from 5.  Hence, its value is 4.  The symbols V, L and D are never written to the left of a symbol of greater value, so V, L and D are never subtracted.  For example, we write 15 as XV and not VX. The symbol I can be subtracted from V and X only. For example, the value of IV is four and the value of VI is six.  The symbol X can be subtracted from L, M and C only.  For example, X is subtracted from L to arrive at 40, which is represented by XL

Estimation of the Numbers

Estimation of the Numbers The estimation of a number is a reasonable guess of the actual value.

The estimation of a number is a reasonable guess of the actual value.  Estimation means approximating a quantity to the accuracy required.  This is done by rounding off the numbers involved and getting a quick, rough answer.  The numbers 1, 2, 3 and 4 are nearer to 0.  So, these numbers are rounded off to the lower ten. The numbers 6, 7, 8 and 9 are nearer to 10.   So, these numbers are rounded off to the higher ten. The number 5 is equidistant from both 0 and 10, so it is rounded off to the higher ten.  Eg: (i)  We round off 31 to the nearest ten as 30 (ii)   We round off 57 to the nearest ten as 60 (iii)  We round off 45 to the nearest ten as 50 The numbers 1 to 49 are closer to 0.   So, these numbers are rounded off to the nearest hundred. The numbers 51 to 99 are closer to the lower hundred. So, these numbers are rounded off to the higher hundred. The number 50 is rounded off to the higher hundred. Eg: (i)  We round off 578 to the nearest 100 as 600. (ii)  We round off 310 to the nearest 100 as 300. Similarly, 1 to 499 are rounded off to the lower thousand, and 501 to 999 to the higher thousand. The number 500 is equidistant from both 0 and 1000, and so it is rounded off to the higher thousand.  Eg: (i)We round off 2574 to the nearest thousand as 3000. (ii)We round off 7105 to the nearest thousand as 7000. Estimation of sum or difference: When we estimate sum or difference, we should have an idea of the place to which the rounding is needed.

Eg: (i)  Estimate 4689 + 19316 We can say that 19316 > 4689 We shall round off the numbers to the nearest thousands.  is rounded off to 19000 4689 is rounded off to 5000 Estimated sum: 19000 + 5000=24000 (ii)  Estimate 1398-526 We shall round off these numbers to the nearest hundreds.  1398  is rounded off to 1400 526 is rounded off to 500 Estimated difference: 1400-500=900 Estimation of the product: To estimate the product, round off each factor to its greatest place, then multiply the rounded off factors.  Eg: Estimate 92 x 578 The first number, 92, can be rounded off to the nearest ten as 90. The second number, 578, can be rounded off to the nearest hundred as 600. Hence, the estimated product =90 x 600 = 54,000 Estimating the outcome of number operations is useful in checking the answer.

Comparing Numbers

Comparing Numbers The arrangement of numbers from the smallest to the greatest is called ascending order.

The arrangement of numbers from the smallest to the greatest is called ascending order.   Ex: 2789, 3560, 4567, 7662, 7665 The arrangement of numbers from the greatest to the smallest is called descending order.  Ex: 7665, 7662, 4567, 3560, 2789 If two numbers have an unequal number of digits, then the number with the greater number of digits is greater. If two numbers have an equal number of digits, then the number with the greater digit is greater. The greatest single-digit number is 9.  When we add 1 to this single-digit number, we get 10, which is the smallest two-digit number.  Therefore, the greatest single-digit number +1=the smallest two-digit number. The greatest two digit-number is 99. When we add 1 to this two-digit number, we get 100, which is the smallest three-digit number.  Therefore, the greatest two-digit number +1=the smallest three-digit number. The greatest three-digit number is 999.  When we add 1 to this three-digit number, we get 1000, which is the smallest four-digit number.  Therefore, the greatest three-digit number +1=the smallest four-digit number. The greatest four-digit number is 9999.  When we add 1 to this four-digit number, we get 10,000, which is the smallest five-digit number.  Therefore, the greatest four-digit number +1=the smallest five-digit number. The greatest five-digit number is 99999.  When we add 1 to this five-digit number, we get 1,00,000, which is the smallest six digit number.  Therefore, the greatest five-digit number +1=the smallest six-digit number. The number, that is, one with five zeroes (100000), is called one lakh.

The greatest six-digit number is 999999.  When we add 1 to this six-digit number, we get 10,00,000, which is the smallest seven-digit number.  Therefore, the greatest six-digit number +1=the smallest seven-digit number. The number, that is, one with six zeroes (1000000), is called ten lakh. The greatest seven-digit number is 9999999.  When we add 1 to this seven-digit number, we get 10000000, which is the smallest eight-digit number.  Therefore, the greatest seven-digit number +1=the smallest eight-digit number. The number, that is, one with seven zeroes (10000000),is called one crore. Commas are placed to the numbers to help us read and write large numbers easily.  Commas in Indian numeration: As per Indian numeration, the first comma is placed after the hundreds place. Commas are then placed after every two digits. Ex: (i)   88,76,547 The number can be read as eighty-eight lakh seventy-six thousand five hundred and forty-seven.  (ii)5 , 67, 89, 056 The number can be read as five crore sixty-seven lakh eighty-nine thousand and fifty-six.  Use the following place value chart to identify the digit in any place in the Indian system.

Crores Lakhs Thousands Ones Tens Ones Tens Ones Tens Ones Hundreds Tens Ones Commas in international system: As per international numeration, the first comma is placed after the hundreds place. Commas are then placed after every three digits. Ex: (i)   8,876,547 The number can be read as eight million eight hundred seventy-six thousand five hundred and forty-seven.  (ii)56,789, 056 The number can be read as fifty-six million seven hundred eighty-nine thousand and fifty-six. Billions Millions Thousands Ones Hundreds Tens Ones Hundreds Tens Ones Hundreds Tens Ones Hundreds Tens Ones Use the following place value chart to identify the digit in any place in the international system.  Comparison of the Indian and the international numeration systems: Indian Numeration  Crore Ten Lakh Lakh Ten Thousand Thousand Hundred Tens Ones Numbers 10000000 1000000 100000 10000 1000 100 10 0 International Numeration Ten Million Million Hundred Thousand Ten Thousand Thousand Hundred Tens Ones Units of measurement: 1 metre=100  centimetres 1 kilogram = 1,000 grams 1 kilometre = 1000 metres 1 litre=1,000 millilitres

Recycling Paper and Plastics

Recycling Paper and Plastics It is important to reuse things than discarding them as waste.

It is important to reuse things than discarding them as waste. Many nice articles can be made out of waste. Industries use recycled or waste paper to regenerate paper. Paper that is suitable for recycling is called "scrap paper". You can recycle old newspapers, magazines, notebooks and used envelopes, but not waxed paper, oil-soaked paper, paper contaminated with food, carbon paper, thermal fax paper, plastic laminated paper, stickers, and sanitary products or tissues. Steps involved in recycling paper Tear paper into small pieces. Soak these pieces in water for a day. Make a thick paste and spread it on a net or sieve. Let water drain off completely. Use an old cloth or newspaper to remove the extra water from the paste and dry it. Use this paste to get beautiful patterns. Disadvantages of using of polythene bags We use many plastic items such as tooth brush, combs, containers, bottles, shoes, toys, wires, frames and bags every day. Certain parts of vehicles like cars and buses, and electronic goods like radios, televisions and refrigerators, are all made of plastic. All these are useful to us in many ways, but using plastic is very harmful in terms of health and as well as the environment. Plastics are not suitable for storing cooked food because they emit harmful chemicals when they are exposed to high temperatures. Using plastics causes health problems such as heart disease, diabetes and reproductive dysfunction. Harmful gases are emitted from burning plastics, which cause cancer and they kill living beings.

That is why plastics should be disposed in the right way. Plastics that do not contain the chemical, BPA, are usually licensed for storing food items. Plastics thrown casually get into drains and sewages, often blocking the way and causing water-logging. A major cause of the floods in Mumbai, India, in August 2005 was the choking of the drainage system by plastic waste. So polythene bags should not be used for garbage disposal. Measures taken to prevent from the dangerous effects of plastics: Adopt healthy practices such as: Reduce, reuse and recycle plastics. Carry  jute or cloth bags for shopping Do not store food items in plastic bags. Do not burn plastic items. Recycle plastics so that new plastic items can be made. Waste that does not decompose should be put in blue dustbins, while waste that decomposes easily should be put in green dustbins. Vermicomposting Conversion of the waste generated in the kitchen into organic matter with the combined action of earthworms and micro-organisms is called vermicomposting. The organic matter so formed is used as manure for plants.

Garbage Disposal and Vermicompost

Garbage Disposal and Vermicompost A large, low-lying area used to dispose garbage is known as a dump. A garbage dump is also used as landfill.

Garbage Disposal  A large, low-lying area used to dispose garbage is known as a dump. A garbage dump is also used as landfill. Garbage collectors collect waste and then dispose it at garbage disposals. Garbage dumps have flies, cockroaches and mosquitoes, and later turn into breeding grounds for micro-organisms that may cause diseases. That is why these garbage dumps are usually located on the outskirts of a city. When garbage mixes with soil, it takes a longer time to decay. The soil becomes loose and a building cannot be constructed on such a landfill. Moreover, it takes 20 to 30 years for the soil to get ready for construction. Components of garbage Garbage has useful and non-useful components.  Useful garbage components are those that can be decayed easily. The process of decaying is known as composting. Useful garbage components are fruit and vegetable waste, plant and animal waste, tea leaves, coffee grounds and paper. These useful components of garbage are converted into manure in the soil. Non-useful garbage components include polythene bags, plastics, glass and aluminium foils. These take longer to decay. Decaying of these non-useful components is known as decomposition. When non-useful components decay, they release harmful gases that damage the environment. To avoid the adverse impact, these garbage items are sent for recycling. For example, when leaves burn, they release harmful gases and causes air pollution. Moreover, they lead to asthma and lung diseases. That is why leaves should be buried so as to convert them into manure. Vermicomposting The process of preparing compost with the help of red worms is called vermicomposting. The red worm is a type of earthworm that lives in the soil rich in organic matter, which is a combination of nitrogen-rich and carbon-rich material with plenty of moisture and microbes.

Method of Vermicompositing A vermicomposting pit is made with a wooden box or big cement rings. A mesh is spread at the bottom of the pit. Vegetable waste, fruit waste, waste paper which is not shiny or coated with plastic, is spread over the mesh. Water is sprinkled to create moisture so that the red worms can live. A vermicomposting pit takes nearly two to four weeks to completely convert waste into manure. Waste material that is rich in oils, salt, meat and vinegar stops the growth of red worms. These red worms have a special structure called gizzards with which they grind food material. A red worm eats food equal to its weight every day. Red worms do not survive in too hot or too cold conditions.

All about Air

All about Air Air supports life on earth

Air supports life on earth. Air helps in the scattering of seeds and pollens of plants. Animals use air for respiration. Plants use air to prepare their food. Air is present everywhere. Atmosphere is a thin layer of air surrounding the earth. The atmosphere is dense at the surface of the earth and becomes thinner as one moves up. Air is: Transparent Colourless Occupies space The movement of air is called breeze or wind depending on its velocity or speed. The following are the various components of air: Nitrogen Oxygen Carbon dioxide Water vapour Smoke and dust particles

Nitrogen Is the major component of air Does not support burning Oxygen: Is the second largest component present in air Supports burning Smoke and dust particles present in air are harmful for the body. Animals and humans breathe in oxygen and give out carbon dioxide during respiration. Plants taken in carbon dioxide present in the atmosphere to make food and release oxygen into the atmosphere.

Effects of Rainfall - Draughts and Floods

Effects of Rainfall - Draughts and Floods Water is used in our day to day life.

Uses of Water Water is used in our day to day life. Water is used for everyday needs such as brushing, bathing, washing, cleaning etc. Farmers use ground water to water their fields. Many industries use ground water to produce everything from paints and fabric to leather and chemicals. So ground water is used for many purposes. Moreover the decline in the number of trees, excess usage of water and the presence of concrete in the areas does not allow the rain water to seep into the ground which is the reason for the shortage of water. Droughts Due to lack of rains the wells, lakes, ponds get dried up and thereby creating water scarcity and as result droughts are possible. If there are no rains, then the soil becomes more dry and patchy. Droughts occur when there are no rains for a longer period of time. There is less rainfall because trees are cut down. Droughts results in drying up of the crops and vegetation and this effects the availability of food for villages and food for the other animals. Finally this leads to malnutrition in humans. Floods Due to heavy rainfall the water levels in ponds, lakes rises to a greater extend and the rise in the water level of these water bodies causes the excess water to spread across causing floods. Floods wash out the living beings such as fish and other animals etc. and they create great havoc to the mankind. Once the rains stops the flood water receded, fish, cattle and other animals were left dead.     Floods cause lot of harm to the living beings and there will be loss in property also.

Rain Harvesting Harvesting is a method to collect rain water and store the rain water. The purpose of harvesting rain water is that two thirds of the earth is covered with water. Ocean and sea water contains many dissolved salts and cannot be used for drinking, agriculture and domestic purposes. So constant use of ground water results in scarcity of groundwater. So rain harvesting clears the problem of depleting the ground water. Technique involved in rain harvesting First collect the rain water at the rooftop and then allow the rain water to travels through the pipes or drains and then attach a wire mesh to the mouth pipe which filters large fragments such as leaves etc. This water is transported to the water tanks. These tanks contain layers of sand, gravel, charcoal that will filter the dirt and other impurities from rain water. The water stored in the tank will then be transported to an underground pit which will help water to seep back into the ground. Rain harvesting solves the problem of depleting the ground water and droughts.

Water Cycle

Water Cycle HOur Earth is covered by two-thirds of water, but most of the water is not portable and contains salt

Our Earth is covered by two-thirds of water, but most of the water is not potable and contains salt. Water is used for various activities such as agriculture, industries, cooking, cleaning utensils, bathing, washing clothes, and, most importantly, for drinking. Ponds, wells, streams, lakes and rivers are the different sources of drinking water.They are supplied water by the oceans and seas.Oceans and seas supply water to other water bodies through the water cycle. The circulation of water from the oceans and the surface of the earth, to the air as water vapour, and its return to the ocean as rain, hail or snow, is called the water cycle A variety of salts, like sodium chloride, calcium, magnesium and potassium, are present in saline water. The evaporation of water takes place in the water cycle, leaving the salts behind in the ocean. The water present on the surface of the ocean evaporates by the sun’s heat. This process of conversion of water from liquid state to vapour state is called evaporation. The sun warms up the surrounding air as well. Evaporation takes place faster in direct sunlight, than in a shady area. Evaporation also takes place from wet clothes, fields, ponds, lakes and rivers. Plants take in water to grow as well as to prepare their food.

They retain the water they need and release the excess water into the air as water vapour through the stomata of the leaves and the stem. This process is called transpiration. Thus, water is mainly evapo-transpirated to the air from land, water bodies and plants. The evaporated water is carried away by warm air.As the warm air moves higher from the surface of the Earth, it starts to cool down. It is because the water vapour present starts to condense to form tiny water droplets. These droplets float in the air and form cloud and fog. All these droplets collect to form bigger drops of water. Some of them may become too heavy to remain in the sky and fall down as rain. This process is known as precipitation. If the air is too cold, the water drops can become snow or hail and may settle on the top of a mountain. When these snow or hail melts, they can become part of a river or a stream. Thus, the water that is evaporated from the oceans or seas is again condensed to form water and fills up the rivers and seas. Rain water also seeps into the ground to form ground water. This circulation of water is called the water cycle.

Characteristics of Living Things

Characteristics of Living Things Human beings, animals and plants - all need food to survive.

Human beings, animals and plants - all need food to survive. Trees, creepers, birds, flowers, insects, animals and seeds are all livings things. Soil, bench, water, air and dry leaves are all non-livings things. The characteristics of livings things are: Livings Things Need Food Livings things need food to survive and grow. Food makes the body grow faster, and gives energy to the body to help it perform the life activities. For example, plants produce their own food by the process of photosynthesis, and grow. Animals depend on plants and other food for their survival. Livings Things Grow As livings things take food, they get more and more energy and grow faster. All living things grow continuously. Livings Things Respire Respiration is the process of breathing in and out. Living things take oxygen into the body as they breathe in and release carbon dioxide as they breathe out. The oxygen that enters the body during respiration helps the body to create energy from the food consumed. Some animals have special organs that help them in the process of respiration. For example, the gills of fish help them to absorb oxygen dissolved in water. Earthworms breathe through their skin. Plants have tiny pores on the leaves that help them to breathe. Plants respire day and night, but breathe out oxygen during the day. Plants release more oxygen while producing their food than they release during respiration. Livings Things Repond to Stimuli Stimulus is a change of some kind in the environment of a living organism. Every living thing responds in some way or the other to stimuli. The response in plants to stimulus can be observed easily.

For example, a plant called touch-me-not closes its leaves when touched. Also, the Evening Primrose blooms only during the night, while the flowers of Mentzelia Mollis close after sunset. Livings Things Excrete The process of eliminating wastes from the body is called excretion. Livings things need food, but they only absorb some amount of it for various processes, while the remaining food needs to be eliminated from the body. For example, plants eliminate harmful waste substances in the form of secretions such as resins and gums, whereas some plants store the harmful substances without any difficulty. Livings Things Reproduce All livings things reproduce. Some animals lay eggs, while others reproduce by giving birth to young ones. Plants produce seeds that can germinate into a new plant, but there are some, such as potato and rose plants, which reproduce through other parts. Livings Things Move Even though plants are livings things, they cannot move as their roots are fixed in the soil. However, the substances produced and required for their growth, such as water, minerals and food, move from one part of a plant to another. Some plants show some restricted movement. Animals have various modes of locomotion. Livings Things Die All livings things must die one day or another. Plants and animals die. All livings things possess these characteristics, whereas non-livings do not have these characteristics.

Types of Habitat

Types of Habitat Habitat is the place that is natural for the life and growth of an organism.

Terrestrial Habitat Habitat is the place that is natural for the life and growth of an organism. Now let us discuss how animals and plants adapt themselves for the terrestrial and aquatic habitats. Terrestrial habitat: All the deserts, mountains and forests and plain lands has come under terrestrial habitat. Camels have long legs for adaptation. Snakes and rats live in burrows and come out only during the night when it is cool. Xerophytes or desert plants shows some adaptations to sustain in the desert conditions. In desert plants, the leaves are either absent or reduced to spines as in cacti. The leaf-like structure seen in cactus is its stem and it carries photosynthesis. The roots grow deep into the soil for absorbing water. The reduced leaf and the thick waxy layer of stem minimise transpiration. The plants and animals in the mountain habitat show some adaptations. Most of the trees in cold mountains are cone shaped. The leaves are also very thin and look like needles For the sliding of water and snow during rains and snowfall. Animals in mountain areas have long hair and thick skin to protect them from cold climate. Thick fur all over Bodies of Yak and Snow Leopard protects them from the cold climate. The mountain goat, have strong hooves that help them run on the mountain slopes easily The animals living in the grasslands show some adaptations. Lions live in forests and prey on other animals, like deer, for food. The lions brown skin colour blends easily with the colour of dry grass in grasslands and helps in the catching the prey. They have strong claws to tear and eat their food. The eyes of the lion in front of its head helps in identifying the prey from long distances. Deeers  have long ears to help them sense the presence of a predator.

Deers  have eyes on the side of its head to look in all directions for danger and have long legs to run away from predator. Aquatic Habitat All the fresh water and marine water bodies , has come under terrestrial habitat. Fish have special features that help them to live in water. They have streamlined bodies, which reduce friction and allow them to move freely in water. Sea animals like the octopus and the squid do not have streamlined body as they stay deep insidethe ocean on the ocean bed, but make their body streamlined when they move in the water. Sea animals, like fish, octopus and squid have gills that help them to absorb the dissolved oxygen from the water they drink! Dolphins and whales have blowholes to breathe in air when they swim close to the surface of the water and there by stay inside the water for a long time without breathing. In general the aquatic plants have much smaller roots and helps the plant in holding on the surface. Stems are long and light.  Leaves and Submerged plants such as Ulva has narrow and ribbon-like leaves. These allow the plants to bend themselves in the direction of the flow of water.In milfoil, leaves are highly dissected, making water to easily flow without Frogs usually live in ponds and lakes. A frog can live both in water and on land. Frogs have strong hind legs to hop on land and webbed feet to swim in water. Frogs also have a membrane called the nictitating membrane on their eyes. This membrane helps protect their eyes inside water.

Habitat and Adaptation

Habitat and Adaptation Livings things exist in most places. Life exists even in open volcanoes.

Livings things exist in most places. Life exists even in open volcanoes. The term habitat refers to the surroundings where organisms live. Every habitat is home for a certain living creature. Habitat includes both living and non-living components. Plants and animals have different features that help them to survive in their own habitat. Habitat can be terrestrial or aquatic. Terrestrial habitat refers to the land where all plants and animals survive. It includes deserts, forests and grasslands, as well as coastal and mountain regions. For example, camels and cactus plants live in deserts only. Aquatic habitat refers to the water where plants and animals survive. Aquatic habitat includes rivers, ponds, lakes, ocean and swamps. For example, fish live in water. Adaptation: Plants and animals develop certain features or certain habits that help them survive in their surroundings, and this is known as adaption. Different living creatures adapt to their habitats in different ways. For example, fish have gills that help them to live in water and use the oxygen dissolve in it. Plants that live in water have special tissues that help to take in dissolved gas from water. For example, the ulva has ribbon-like leaves. It takes thousands of years for a livings being to adapt to its habitat.

Acclimatisation: The small adjustments by the body to overcome small changes in the surrounding atmosphere for a short period of time are called acclimatisation. The components in a habitat are broadly classified into two types. They are biotic and abiotic components. Biotic components include all the livings organisms in a habitat. Abiotic components include all the non-living things in a habitat. These include air, rocks, water, sunlight and heat. All livings things depend on the abiotic components for all their needs. The abiotic components are very useful for the survival of the biotic components in a habitat. For example, sprouting is the first step where a new plant grows from a seed. The sprouting of a seed depends on abiotic components such as air, water, light and heat. The population of some species of turtles has declined due to the change in the earth’s temperature. Some popular theories believe that dinosaurs became extinct because of the changes in the earth’s temperature millions of years ago.

Gait of Animals

Gait of Animals Earthworms move easily on hard and slippery surfaces.

Gait of earthworms Earthworms move easily on hard and slippery surfaces. Earthworms have tiny, stiff hair-like projections, called bristles, under their body. They grab the soil with the help of these bristles. Earthworms first stretch and then contract their muscles to move. As a result, they cover only a small distance with every move. A slimy substance secreted by the earthworm helps it to move. Earthworms eat their way through the soil. They throw away undigested food, which improves the quality of the soil. Gait of snails The outer skeleton of the snail, the shell, is made of calcium carbonate. The snail pulls this shell along as it moves. The snail can even hide its head inside the shell. The strong muscular foot below the shell can protrude. The under surface of the muscular foot is lubricated with mucus. Waves of muscular contractions along this surface help a snail move. The mucus also reduces the risk of injury from sharp objects. That is why snails can walk over sharp objects like blades without getting hurt. Gait of cockroaches The cockroach has three pairs of legs that help it to walk, and two pairs of wings that help it to fly. A cockroach moves its legs with the help of muscles near the limbs. It uses its breast muscles help to move its wings and fly. A cockroach can walk, fly and even climb. A cockroach can move in different terrains like sand and wired meshes because of the spines on its legs.

Gait of birds A bird has a body best suited for flying. Its wings are actually modified forelimbs. Birds can fly easily with the help of these bony forelimbs. Birds have light and hollow bones. The breast bones hold the muscles of flight that help them to flutter their wings. The tail controls the direction of flight. Birds have very strong shoulder bones. They don’t have the urinary bladder, which helps them to fly easily. They can walk and perch on trees with the help of their hind limbs. Gait of snakes Snakes move in S-shaped loops and in a zigzag manner. They cannot move in a straight line. They have difficulty in moving on very smooth surfaces. Snakes have a long back bone and many interconnected muscles that help them to slither. They have muscles connecting the backbone, ribs and skin. Snakes move in grass, sand and water. Snakes do not have arms or legs, but even then, they can climb trees. Gait of fish Fish have a streamlined body, which helps them move fast in water. Fish swim with the help of their fins. The tail moves from side to side, and helps the fish swim in the right direction. Some fish, however, move by bending their bodies from one side to another in quick succession, which produces a thrust that helps it move forward.

Bones and Skeleton

Bones and Skeleton The skeleton is a framework of all the bones in the human body

The skeleton is a framework of all the bones in the human body.
The skeleton consists of the skull, hand bone, shoulder bone, rib cage, pelvic bone, backbone, leg bone and cartilage.
The skull protects the brain.
The shoulder has the ball and socket joint that helps the arm swing.
The rib cage protects the lungs, heart, stomach, abdomen and liver.
The backbone runs from the top of the skeleton to the bottom of the skeleton. It is connected to all the bones.
The pelvic bone protects the lower abdominal organs such as the urinary bladder, rectum and uterus.
Cartilage is a soft bone tissue that connects joints. It is present in external parts like the ear and nose.

Joints and their Types

Joints and their Types The point at which two separate bones meet is called a joint.

The point at which two separate bones meet is called a joint. There are four types of joints in the human body. They are: Ball and socket joint: One end of a bone is rounded and ball-like, and fits into a cup-like depression of the other bone. This joint provides movement in any direction. Shoulder joints and hip joints are examples. In the shoulder joint, the head of the humerus fits into a socket of the shoulder girdle. In the hip joint, the large ball-like head of the femur fits into the deep socket of the hip girdle. Hinge joint: This joint moves like a hinge in one plane only, just like the hinge of a door. The elbow joint between the humerus and the ulna. The joints between the bones of the fingers and toes, and less perfectly, the knee joint. Hinge joints usually give sufficient power, because there is less danger of twisting at the joint.

Pivot joint: One bone rotates over a pivot-like end of the other bone. The skull rotates on the upper end of the back bone. Fixed Joint: In this joint, no movement is possible between the two bones. The sutures between the bones of the cranium are an example.

Parts of a Flower

Parts of a Flower The flower is the reproductive part of a plant.

The flower is the reproductive part of a plant. The parts of a flower include sepals, petals, stamen and pistil. The hard, leaf-like structures around the base of a flower are called its sepals. They protect the bud before it blooms into a flower. The sepals are collectively called the calyx. The number of sepals varies from plant to plant. The brightly coloured portions of a flower that attract insects and birds for pollination are called petals. Like sepals, the number of petals also varies from plant to plant. The petals are collectively called the corolla. In some flowers, the petals and sepals combine to form a round shape, which is called the tepal. The stamens and the pistil are the reproductive parts of a flower. The stamen is the male reproductive part of a flower. The small tube with a little bulge at the end of a stamen is called the filament. The filament has a yellow sac called the anther. This yellow sac contains pollen grains, which contain male reproductive cells.

Like sepals and petals, every flowering plant differs in the number of stamens, too. The female reproductive part of a flower is the pistil. It consists of three parts – the stigma, the style and the ovary. The upper end of the pistil is called the stigma, where pollen grains get deposited and enter the pistil. The narrow tubular part is called the style, which connects the stigma to the lower part of the pistil. The lower bulgy part of the pistil is called the ovary. It contains ovules. The ovary can be cut longitudinally or transversely to see the female reproductive cells, ovules, which appear as bead-like structures. The number and arrangement of ovules differ in different flowering plants. Like the stamens, the number of pistils also varies from flower to flower.

Parts of a Plant

Parts of a Plant The different parts of a plant are the roots, stem, leaves, flowers and fruits.

The different parts of a plant are the roots, stem, leaves, flowers and fruits. The roots of a plant are mostly seen underground and look brown in colour. The tiny thread-like structures over the roots are the root hair. The tip of the root is called the root cap. Roots are of two types - tap root and fibrous roots. Some plants have a primary root that grows more or less straight down into the soil, and is tapered towards the end. This main root is called the tap root. There are many smaller roots that branch out from the tap root, called lateral roots. Examples of plants with tap roots are hibiscus, carrot, turnip and sunflower. Some plants have many lateral roots that start from the base of the stem. These are called fibrous roots. Examples of plants with fibrous roots are banana, grass and onion. The roots hold the plant firmly in the soil, thereby serving as an anchor to the plant. One of the main functions of the roots is to absorb water and nutrients from the soil for the growth of the plant. Sometimes they also store sugars and carbohydrates. The stem holds the leaves, flowers and fruits in a plant.

The vascular tissue inside the stem helps to transport water and nutrients from the roots to the leaves, and food from the leaves to the roots. Plants release excess water in the form of water vapour through minute openings in the leaves, called the stomata. This process is known as transpiration. The different parts of a flower include sepals, petals, stamen and pistil.                     The green leaf-like parts surrounding the bud are called the sepals. The brightly coloured parts of a flower are called the petals. The male part of a flower is called the stamen, and the female part is called the pistil. The male and female parts of a flower are involved in the formation of fruit in a process called fertilisation.

Categories of Plants

Categories of Plants A herb is a non-woody plant that has green and tender stems with few branches and is usually short

A herb is a non-woody plant that has green and tender stems with few branches and is usually short. Herbs have a variety of uses including adding flavor to food, providing medicine for diseases and in some cases even adding a spiritual touch. Shrubs are taller than herbs and have stems branching out from the base. The stems of shrubs are hard not but thick. A common place where shrubs are grown is known as shrubbery. A tree is a woody plant that has many branches on a single stem. Trees  benefit us by preventing soil erosion, maintaining the carbon dioxide content in the air and in building huts and making furniture. Threes are categorised based on their height, width of their trunk, their overall size, and of course their age. Creepers are plants with weak stems and hence cannot stand straight. They grow on the ground. Creepers have a tendency to develop new plants on their own. A few creepers could cause allergies or skin problems if touched. Climbers are plants that need support from other structures to grow and spread. Climbers can either move horizontally or vertically unlike creepers that move only horizontally. Climbers attracts insects and reptiles because of their brightly coloured flowers and fragrance.

Deficiency Dieseses

Deficiency Dieseses Occurs mainly due to the deficiency of one or more nutrients in the diet over a long period of time.

Diseases or disorders occur mainly due to the deficiency of one or more nutrients in the diet over a long period of time. For example, wheat is rich in carbohydrates, but poor in nutrients like proteins and fats. Too much intake of wheat products results in a deficiency of proteins and fats, which reduces growth.  Lack of proteins also results in stunted growth, skin diseases, swelling of the face and discolouration of the hair, and even causes diarrhoea. So a balanced diet is required to avoid deficiency diseases. Diseases caused by deficiency of minerals: Lack of iron in the diet leads to a deficiency disease called anaemia. The symptoms of anaemia are headache, dark patches under the eyes, weakness and feeling tried. A balanced diet should, therefore, include iron-rich foods such as apples, fish and raisins to avoid anaemia. Lack of iodine in the diet leads to a deficiency disease called goitre. In adults, goitre results in swollen glands at the throat. In children, iodine deficiency causes stunted mental and physical development. Iodine deficiency can be avoided by using iodised salt in the diet. Lack of calcium in the diet makes the bones weak and brittle, and also causes tooth decay. Milk, eggs and other dairy products contain calcium and give strength to the bones and teeth.

Diseases caused by deficiency of vitamins: Lack of vitamin A in diet causes loss of vision. Symptoms include night blindness, i.e. poor vision in dim light. Eating food rich in vitamin A, such as carrot, mangoes, butter and egg yolk, helps avoid loss of vision. Lack of vitamin B1 in the diet causes a deficiency disease called beriberi. The symptoms are loss of weight and weak muscles. Food rich in vitamin B1, such as beans, meat, eggs and corn, helps avoid beriberi. Lack of vitamin C in the diet causes a deficiency disease called scurvy. The symptoms of scurvy are bleeding gums. Moreover, wounds take longer to heal. Oranges, tomatoes, lemon, guavas and amla are rich in vitamin C, so eating these helps avoid scurvy. Lack of vitamin D in the diet causes a deficiency disease called rickets. The symptoms are soft and bent bones. The diet should include fish, eggs, milk and butter to avoid rickets. In addition, exposure to sunlight produces vitamin D in the body.

Nutrients and Balanced Diet

Nutrients and Balanced Diet All living organisms require food. Food has six types of nutrients - carbohydrates, proteins, fats, vitamins, minerals and water.

All living organisms require food. Food has six types of nutrients - carbohydrates, proteins, fats, vitamins, minerals and water. These are essential to perform all daily and metabolic activities. Carbohydrates are compounds of carbon, hydrogen and oxygen, always in the ratio of 2:1:1. They are oxidised in the cells to release energy. Carbohydrates include sugars, starch and cellulose. Carbohydrates are oxidised in the body in the form of sugars. They provide instant energy. When oxidised in the body, one mole of glucose releases 686 kilocalories of energy.  They are mainly present in rice, potato, banana, etc. Proteins are composed of carbon, hydrogen, oxygen and nitrogen. Nitrogen is the most essential element in proteins. Some proteins contain sulphur and phosphorus. Amino acids are the simple, smaller units of proteins. Proteins provide chemical material for the growth and repair of the body cells and tissues. In an emergency, they may also oxidise to release energy. Food rich in proteins includes lean meat, fish, eggs, milk, cheese, nuts, beans, peas, etc. Fats are also composed of carbon, hydrogen and oxygen. Fats have very little oxygen content, though.. They produce more energy than carbohydrates do. Fat below the skin protects the body against rapid loss of heat. It serves as a solvent for fat-soluble vitamins. It is an important form for storage of food. Common foods rich in fats are butter, cream, vegetable oils, meat, and fish liver oils. Mineral salts are needed in the diet in small quantities. These are obtained from table salt, green vegetables and fruits.  Some important minerals are:   Calcium, required for: Strengthening bones and teeth Blood clotting Muscle contraction Rich sources: Milk, meat, eggs, fish, pulses, vegetables, etc. Phosphorus, required for:

Strengthening bones and teeth For production of ATP in during cellular respiration Conduction of nerve impulses Rich sources: Milk, meat, eggs, fish, pulses, vegetables, etc. Iron, required for: Forming haemoglobin Rich sources: Green leafy vegetables, liver, etc. Iodine, required for: Proper working of thyroid Rich sources: Vegetables, mineral water and iodised salt Vitamins are chemical substances that help maintain a healthy body. Vitamins A, D, E, and K are fat soluble and can be stored in the body. Vitamin B complex and vitamin C are water soluble and cannot be stored for a long period of time. Vitamin A: Promotes growth, vision. Present in butter, egg yolk, milk, carrot, etc. Vitamin D: Helps the body to absorb calcium and phosphorus to form bones and teeth. Present in fish liver oils, milk, eggs, etc. Vitamin E: Prevents the oxidation of vitamin A. Present in meat, milk, whole wheat, etc. Vitamin K: Helps in clotting of blood during injuries. Present in cabbage, spinach, leafy vegetables Vitamin B complex:  Needed for a healthy brain, nerves and muscles. Present in wheat, rice and liver. Vitamin C:  Helps fight diseases like the common cold. Present in oranges, tomatoes, lemons and guavas. Water: Helps the body to get rid of toxic wastes through urine and sweat, and to absorb the nutrients in food. Balanced diet: The diet that contains all the principle constituents of food in proper quantity.

Test For Starch, Proteins and Fats

Test For Starch, Proteins and Fats Different food items contain different types of nutrients

Different food items contain different types of nutrients. Nutrients are chemical components in food that are required for releasing energy and helps in growth. Carbohydrates, proteins, fats, vitamins and minerals are important nutrients found in food. Carbohydrates and fats mainly provide energy. Proteins mainly help in growth. Starch and sugar are the two kinds of carbohydrates found in food. To test the presence of starch in a food item, you need to: Take small quantity of the food items to be tested. Put 2-3 drops of iodine solution on it. Observe the colour of the food item. Blue-black colour indicates the presence of starch in the tested food item. To test for the presence of proteins in a food items, you need to: Take a small quantity of the food items to be tested. Grind/mash/paste/powder the food item. Put the food item into a test tube. Add 10 drops of water to the test tube. Add two drops of copper sulphate solution to the test tube. Add 10 drops of caustic soda solution and shake the test tube. Observe the colour of the mixture. Violet colour indicates the presence of proteins in the tested food item.

To test for the presence of fats in a food item, you need to: Take a small quantity of the food item to be tested. Wrap the food item in a small piece of paper. Crush the food item wrapped in the paper. Straighten the paper. Dry the paper by keeping it in sunlight for a while. Observe the paper. An oily patch on the paper indicates the presence of fats in the tested food item.

Sources of Food

Sources of Food All ingredients is a component of a mixture

All ingredients is a component of a mixture. Certain food items are made with few ingredients, but some are made with many ingredients. Some ingredients are common for several food items. Vegetables, cereals, pulses, fruits and spices come from plant sources. Mean, poultry, fish and milk products come from animal sources. Animals are categorized based on their eating habits into herbivores, carnivores and omnivores. Herbivores are animals that eat only plants and plant products. Carnivores are animals that eat meat. Omnivores eat both plants and animals.

Changes around us

Changes around us Every day, we see different types of changes around us, like day turning into night, the season changing from winter to summer

Every day, we see different types of changes around us, like day turning into night, the season changing from winter to summer, melting of ice to water, cooking of food, and so on. Changes take place around us all the time. However, all changes are the same. We get back the original substance in some, and can’t get them back in others. A reversible change is a change that can be undone or reversed. Melting is an example of a reversible change. Boiling, evaporation and condensation are all examples of reversible changes. For example, if you could capture all the steam that is made when a kettle boils, you could turn it back into water by cooling it. Some other examples of reversible changes are the melting of ice, folding a paper and blowing a balloon. A blacksmith changes a piece of iron into different tools. For that, a piece of iron is heated to red hot. This also softens it. It is then beaten into the desired shape. It is a reversible change.

An irreversible change is a permanent change that cannot be undone. In an irreversible change, new substances are formed. Cake batter is made from eggs, flour, sugar and butter. Once the cake has been baked, you cannot get the ingredients back. Heating a substance can cause an irreversible change. Cooking is another example. We cannot get back the substances that we originally started  with Mixing substances can also cause an irreversible change. For example, when vinegar is mixed with bicarbonate of soda, you can observe the release of carbon dioxide gas in the form of bubbles. Again, here, we cannot get back the original substances. Some other examples of irreversible changes are the digestion of food and heating of lime stone. The burning of wood is also an irreversible change. Once wood is burned, it changes to ash, and we cannot get back the wood again. Finally, our growth itself, as you can see, is an irreversible change.

Methods of Separation II

Methods of Separation II Grains can be separated from dirt by sedimentation and decantation. When water is added to the grains, the dust and dirt dissolve in the water, making it muddy.

Grains can be separated from dirt by sedimentation and decantation. When water is added to the grains, the dust and dirt dissolve in the water, making it muddy. Thus, the dirt and grains are separated. The grains settle at the bottom because they are heavier. This process of the settling of the heavier substance is called sedimentation. Now, the grains can be separated by simply pouring out the water. This process is called decantation. Oil and water can also be separated by decantation and sedimentation. Water is heavier than oil, so it settles at the bottom if left alone for some time. The oil can then simply be poured out. The water left behind can be further cleaned using a filter paper. While water passes through the fine pores of the filter, dirt will sift out, leaving the water clean. This process of using a filter to separate substances is called filtration.

Salt and water from salty water can be separated by evaporation. We need to boil this water so that its temperature rises and it converts into steam. This process is called evaporation. The steam turns back into water when it comes in contact with a cold metal lid. This process is called condensation. A mixture of sand and salt can be separated by combination of methods. The first method is sedimentation and decantation. This mixture is put in water and left for the sand to settle for some time. Then, we will decant the salty water, which will separate the sand from the mixture. Now the salt can be separated from the water by evaporation. The water will boil away, leaving the salt behind. So, the mixture of the sand, salt and water has been separated successfully using a combination of sedimentation, decantation, evaporation and condensation.

Methods of Separation I

Methods of Separation I There are various methods for separating substances, such as handpicking, threshing, winnowing and sieving.

There are various methods for separating substances, such as handpicking, threshing, winnowing and sieving. Handpicking allows the good grains to be separated from the waste and impurities. Handpicking is the basic method for separation of substances. It involves simply picking out substances by hand and separating them from others. The substances being separated may be impurities that have to be thrown away. It could also be that both the substances being separated are useful – such as separating green grapes from black ones. The method of separating the grain from the stalk is called threshing. It is basically the beating of dry stalks to shake off the dried grains. It can be done by hand, by cattle or by machines. Traditionally, threshing was done by hand, but cattle help do the job quickly. Nowadays, threshing machines are also used to separate large quantities of grain quickly.

Even though the large stalks can be separated from the grains by threshing, the grains still have dried husk and chaff, which have to be separated and thrown away before the wheat can be used. This method is called winnowing. The husk is blown away as it is much lighter than the grain. So, when the grains are gently dropped to the ground, only the wheat grains collect there, while the husk blows away. Sieving is a method of separating substances that are of different sizes. For example, wheat flour has some fine powdered wheat as well as some bigger impurities. When it is put this through a sieve, the fine powder falls through the small holes in the sieve, while the thicker impurities remain as they are too big to pass through these holes. The substances are thus separated.

Properties of Materials

Properties of Materials Objects are categorised on the basis of their shapes, the materials they are made up of, and the properties of these materials.

Objects are categorised on the basis of their shapes, the materials they are made up of, and the properties of these materials. All objects around you have definite shapes. For example, eggs are oval and ice-cream cones are conical in shape. Objects can be classified on the basis of their shapes. Objects can be made from many different kinds of material, such as plastic, wood, glass, metal, cotton, paper, leather, wool, rubber, and even soil. Therefore, all objects can be grouped on the basis of the material that they are made from. Sometimes, the same object can be made from different materials. For instance, a pen could be made from metal or plastic, your shoes could be made from leather or cloth, and even the tumbler that we drink from could be made from plastic, glass or metal. Bottles could be made from plastic or glass, and chairs could either be wooden, metallic or plastic. Notebooks, greeting cards, newspapers and calendars are all made from paper. Similarly, shoes, belts and bags that are made of leather form another group. So, objects can be grouped according to the materials they are made of. Gold, copper, iron and aluminium look shiny, and are called lustrous materials. Most metals have this property. Other materials like wood or plastic, are non-lustrous. Metals like iron may react with the moisture in the air, which makes them lose their lustre and look dull.

Iron is a good example of a very hard material. Materials that are considered hard are difficult to compress, while those that can be compressed or scratched easily are called soft materials. Cotton and sponge are examples of soft materials. Objects can be classified on the basis of properties of the materials that they are made from. Solubility is another important property of a material. Substances that completely dissolve in water are said to be soluble in water. Substances like sand and sawdust do not dissolve in water even if you stir them very well. They are said to be insoluble in water. Some gases can dissolve in water. For example, oxygen dissolved in water is useful for plants and animals that live underwater. Lighter materials like paper, leaves and wood float on the surface of water, while heavier objects, like those made from iron, sink in water. Materials like glass or plastic are called transparent as you can see through them. Objects made from transparent materials allow you to easily see what they contain. Materials like wood, cardboard and metal are opaque, as you cannot see through objects made from these materials. Some materials like plastic can be transparent or opaque, depending on the use for which the object is meant. For example, try spotting the jar that contains cookies from among these containers! There are some materials that allow you to see through them, though not very clearly. Such materials are called translucent. Butter paper and frosted glass are examples of translucent material. Thus, there are various properties on the basis of which you can group objects. Grouping is useful for locating objects easily, such as on supermarket shelves. It also helps in studying the properties of objects that are in these groups.

Fibres

Fibres Fabrics are made up of strands called yarns, which are made from even thinner strands

Fabrics are made up of strands called yarns, which are made from even thinner strands, called fibres. Cotton, silk, wool and jute are called natural fibres as they are obtained from natural sources. We get cotton and jute from plants. We get silk from the cocoons of silk worms. Synthetic fibres like nylon, polyester and acrylic were invented about a hundred years ago. These are man-made and are not obtained from any plant or animal sources. Cotton fibre is obtained from cotton plants that grow in black soil in a warm climate. In India, cotton is grown in Gujarat, Maharashtra, Andhra Pradesh, Punjab, Haryana, Karnataka, Tamil Nadu, Rajasthan, Orissa and Madhya Pradesh. The cotton plant bears fruits about the size of a lemon, called cotton bolls. The bolls are full of seeds and cotton fibre. They burst open when they are ripe. The cotton fibres are collected by hand from the ripe cotton bolls. This process is called picking. Next, the cotton fibres are separated from the seeds by combing them. This is known as ginning. Earlier, ginning was done by hand, but nowadays, a machine is used. Jute fibre comes from jute plants, which are mainly grown in places that have high temperatures and plenty of rainfall. Jute is cultivated during the rainy season. In India, jute is cultivated in West Bengal, Bihar, Andhra Pradesh, Uttar Pradesh, Assam, Chhattisgarh and Tripura.

The jute plant is generally harvested when it is in the flowering stage. The stems of jute plants are soaked in water for a few days until they start rotting. Then the fibres are separated by hand from the rotting stems. Once the fibres have been obtained, they are made into yarn by twisting the strands together. This process of making yarn from fibre is called spinning. Not just jute, even cotton, silk and other fibres are spun to convert them into yarn. Machines are used for spinning yarn on a large scale. Fabrics like khadi are made by spinning yarn on hand-operated devices like charkhas and taklis. The process of arranging two sets of yarns to produce a fabric is called weaving. Even coconut fibre can be woven into a fabric called coir. Coir is too rough to be made into garments. It is mostly used to make doormats, carpets and other flooring material. In ancient Egypt, flax and cotton plants were cultivated near the River Nile and were used for making fabric. At the beginning of civilisation, people used bark, leaves and animal fur to cover themselves. As people settled down and started farming, they learned to weave vines and animal fleece to make fabrics. In the next stage of civilisation, flax and cotton were woven into garments. In those times, people just draped the fabric to cover themselves. It was only after the invention of the sewing needle that people started stitching their garments. Even today, in older cultures like India, you see people wearing unstitched garments like turbans, saris and dhotis.

Properties of a Magnet

Properties of a Magnet Substances that possess the property of attracting iron are called magnets.

Substances that possess the property of attracting iron are called magnets. The two ends of a magnet are called its poles. All magnets have two poles, and they are called dipoles. A magnet with a single pole doesn't exist. Since poles have high magnetic power, they attract objects easily. The poles of a magnet are named as the north pole and the south pole. In order to identify the poles, the north pole is usually painted in red colour. The other end of the magnet will, therefore, be the south pole. In laboratories, magnets are painted completely red in colour with a white dot to indicate the north pole. The other end will, therefore, be the south pole. A magnet can be cut into two pieces. Each piece will behave like an independent magnet, with a north pole and a south pole. Types of magnets Bar magnets In these magnets, the poles are located at the ends of the bar. Cylindrical magnets In these magnets, the poles are located at the two circular ends of the cylinder. Dumb-bell shaped magnets In such magnets, the poles are located at the two dumb-bell shaped ends. Horseshoe magnets In these magnets, the poles are located at the two free ends of the 'U' shape. Compass A compass is an instrument that is used to find the directions. It has a thin magnetic needle supported from a pivot so that it can rotate freely. The needle is placed over a dial with the directions marked. The entire assembly is placed inside an airtight box.

The north pole of the magnetic needle is painted red. The magnetic needle in the compass points in the north-south direction. By aligning the dial properly, the directions can be found. In the ancient days, an old pointing device, called the south pointing fish, was used to know the directions.  The head of the fish pointed towards the south. Alignment of a compass Take a compass and make sure that the magnetic needle comes to rest. Rotate the box so that the red tip of the magnetic needle coincides with the north mark of the dial. The compass is now aligned. Next, select any object around you. Then, with the help of the compass, identify the direction in which the object lies relative to you. Law of magnets Unlike poles attract each other and like poles repel each other. Artificial magnets Magnets can be made artificially, too. A rectangular iron bar, an iron needle, a blade or an iron nail can be turned into a magnet by rubbing a bar magnet over it. Precautions to protect magnets from losing their magnetic properties Never drop magnets from heights. Never heat a magnet. Do not hammer a magnet. Certain items such as CD's, DVD's, debit cards, credit cards or ATM cards, audio and video cassettes, and mobile phones contain magnetic material.   Keep them away from magnets to prevent damage.

Magnetic and Non-magnetic Materials

Magnetic and Non-magnetic Materials A Greek shepherd named Magnes discovered magnets 4,000 years ago in Magnesia, Greece.

A Greek shepherd named Magnes discovered magnets 4,000 years ago in Magnesia, Greece. The name magnetite has been derived from Magnesia or Magnes. Magnets are named after Magnetite. Magnets attract magnetic materials. Natural rocks that have the property of attracting iron are called naturals magnets.  Magnes discovered a natural magnetic rock, called the lodestone. In the form of a bar, it was used to find directions on the earth, and so the name, ‘lodestone,’ which means the stone that leads.  Lodestone has a compound of iron called magnetite. These natural magnets have the magnetic property of attracting materials like iron.  "Archimedes", the ancient Greek scientist, is believed to have used lodestone to pull nails from enemy ships. Taking the nails out made the ships sink.

Magnetic Materials Materials that are attracted by a magnet are called magnetic materials. Objects made of materials such as iron, cobalt and nickel are magnetic objects. Examples of magnetic materials include iron nail, key, metal spade, needle and metal door handle. Non-Magnetic Materials Materials that are not attracted by magnets are called non-magnetic materials. Modern coins are made of uniform mixtures of different metals so they become non- magnetic. Examples of non-magnetic materials include rubber, coins, feather and leath