A mountain is any natural elevation of the earth surface.
There are permanently frozen rivers of ice. They are called glaciers.
Mountains may be arranged in a line known as the range.
The Himalaya, the Alps and the Andes are mountain ranges.
There are three types of mountains—Fold Mountains, Block Mountains and Volcanic Mountains.
The Himalayan Mountains and the Alps are young fold mountains.
The Aravalli range in India is one of the oldest fold mountain systems.
Block Mountains are created when large areas are broken and displaced vertically.
Volcanic mountains are formed due to volcanic activity, e.g. Mt. Kilimanjaro in Africa
Plateaus
A plateau is an elevated flat land.
The Deccan plateau in India is one of the oldest plateaus.
The Tibet plateau is the highest plateau in the world.
The African plateau is famous for gold and diamond mining.
The lava plateaus are rich in black soil that are fertile and good for cultivation.
Plains
Plains are large stretches of flat land.
Most of the plains are formed by rivers and their tributaries.
In India, the Indo-Gangetic plains are the most densely populated region of the country
Landforms and the People
Humans have been living in different kinds of landforms in different ways.
Sometimes, natural calamities such as earthquakes, volcanic eruptions, storms and floods cause widespread destruction.
The surface of the earth is not the same everywhere.
Mountains, plateaus and plains are different landforms of the earth.
A mountain is a natural elevation of the earth surface. There are three types of mountains—Fold mountains, Block mountains and Volcanic mountains.
A plateau is an elevated flat land. It is a flat-topped table land standing above the surrounding area. A plateau may have one or more sides with steep slopes.
The Deccan plateau is one of the oldest plateaus.
The Tibet plateau is the highest plateau in the world.
Plains are large stretches of flat land. Some plains are extremely level while others may be slightly rolling and undulating
Plains are generally thickly populated regions of the world
Human habitation is found on different kinds of landforms. But population varies on these landforms. Mountains are generally not thickly populated. But plains are the regions where the thick population is found.
The land is precious. We must not use it in a wasteful manner. Construction work of any type should not be carried on fertile land. Also, we should not throw garbage on land. It is our duty to take care of the land or any other natural gift. If we do this we will be conscious citizens.
Erosion: The wearing away of the earth’s surface is known as erosion.
Mountain: A mountain is a natural elevation of the earth surface.
Glacier: Some mountains have permanently frozen river of ice. They are called glaciers.
Range: When mountains are in an arranged line, it is called a range.
Horsts and graben: The uplifted blocks are known as horsts and the lowered blocks are known as graben.
Storehouse: A building where things are stored or kept.
Terraces: One of the series of flat areas of ground which are cut into the side of a hill like steps in order to grow crops there.
Flora: The plants of a particular area.
Fauna: The animals living in an area.
Plateau: A plateau is an elevated flat land. It is a flat-topped table land standing above the surrounding area.
Plain: A plain is a vast stretch of flat land where the thick population is found.
1. The Aryans were nomadic people who came to India from the north-west.
2. They settled down and gradually took to agriculture.
3. Our knowledge of the Aryans comes from the Vedas.
4. The Rigveda gives information about the Early Vedic Age.
5. The period when the Aryans first settled in India is known as the Early Vedic Age (1500 BCE to 1000 BCE).
6. During this period, the kingdoms were tribal in character.
7. The period between 1000 BCE to 600 BCE is known as the Later Vedic Age.
8. The king now became very powerful and the status of women declined.
9. Megalithic burials have been found in many places in India.
10. Inamgoan is believed to have been occupied from 1600 BCE to 700 BCE.
Have you ever heard or recited the Gayatri Mantra? It is from the oldest text in India called the Rigveda. There are four Vedas. The Rigveda is the oldest among them. The Vedic Age is the period during which the Vedas were composed. This period from 1500 BCE to 600 BCE, is often called the Vedic Age.
Earlier, we have read about the Harappan Civilisation. Slowly it declined and by around 1800 BCE, people again began living a simple life in villages. About this time, some people entered India from the north-west. They called themselves ‘Arya’ meaning ‘noble ones’. A new culture developed in India with the arrival of the Aryans. They did not come to India to invade and plunder and go back. They settled down in the plains and took to agriculture. They first settled in seven places in the Punjab region which they called Sapta Sindhu. These Aryans who settled in India are called Indo-Aryans.
STUDY OF VEDAS
Our knowledge of the Aryans comes from the Vedas. The Vedic Age gets its name from the four Vedas. Historians have studied these texts carefully. They provide an insight into the life of the Vedic Age.
LANGUAGES
The Aryans spoke a language called Indo- European which was the ancestor of Sanskrit, Assamese, Gujarati, Kashmiri and many other foreign languages like Latin, Greek, German and Persian. Similar words exist in all these languages. In India, the languages used in the north-east belong to the Tibeto-Burman family. Tamil, Telugu and other languages of the sout belong to the Dravidian family.
The oldest Veda is the Rigveda. It was composed about 1500 BCE and is a collection of 1028 hymns written by rishis. These hymns are in praise of various gods and goddesses. These hymns were considered sacred. For hundreds of years, the Rigveda was passed down by word of mouth. Finally, it was written down in Sanskrit. The other three Vedas were written later and tell us about the Later Vedic Age.
EARLY VEDIC AGE
The period when the Aryans first entered India is known as the Early Vedic Age (1500 BCE to 1000 BCE). The chief source of information about this period is the Rigveda.
Political Organisation
The kingdom was tribal in character. The tribal chief was called rajan. He ruled over the people (jana) and not over any specific area of land. His position was not hereditary. He did not live in any palace and did not collect regular taxes. His main function was to protect the people and lead the army to victory in battle. Battles were fought for land which was essential for agriculture and for pastures for the cattle. He used to receive a large part of the booty collected in battle. He was also called gopati (Lord of Cattle) indicating that protecting and increasing the cattle was his other major role. He received from the people a voluntary offering called ball. The king did not maintain a standing army. The king’s power as kept in check by assemblies such as sabha and samiti. The king dispensed his duties with the help of the purohita (religious advisor) and senani (army chief).
Q. Why was the king called gopati? Why were cattle so important?
Status of Women
Women were treated equally and were allowed some choice in the selection of their husbands. They received education also. Child marriage and sati1 did not exist and widows were not treated badly. Women participated in the sabha, rituals and even chariot races.
History Reveals
The Rigveda has many hymns composed by women and there are references to women sages.
Economic life
The Aryans did not have any fixed territories and they moved from place to place with their cattle and horses. As they began to settle down, they began to practice agriculture. Cattle were the most-valued possession and chief form of wealth. Besides agriculture and cattle rearing, there were many other professions. People were also engaged in trade.
History Reveals
Ships were also used by the Early Vedic people. The Rigveda speaks of ‘?ships with a hundred oars?.
Religion
People worshipped the forces of nature. Much of the Rigveda is full of prayers for these deities. The important gods were Indra, Varun, Surya, Vishnu, Vayu and Yama. Some goddesses were Usha, Savitri and Prithvi. Their favour could be won by sacrifices. They did not make temples or idols. They worshipped through prayers and chanting Vedic mantras.
LATER VEDIC AGE
The period between 1000-600 BCE is known as the Later Vedic Age. We know about this age through the books that were composed during this period.
Samaveda: It is a collection of musical verses from the Rigveda.
Yajurveda: This contains mantras and rituals for sacrifice.
Atharvaveda: This contains chants to cure diseases and ward off danger. The epics, Mahabharata and Ramayana, were also written during this age. They tell us about the political and social setup of that period and are considered religious texts. This age is also called the Epic Age because these two great epics were written during this period.
Political Organisation
Each tribe now occupied a fixed territory which as named after the tribe. Tribes often fought over territories. The term rashtra which indicates territory first appeared in this period. The king became very powerful and his position became hereditary. He lived a luxurious life in a palace. He received regular taxes in the form of food grains or cattle. He appointed officers to collect taxes. He maintained law and order and all major decisions were taken by him. The sabha and samiti assisted him but did not curtail his power. He performed various sacrifices to prove his strength and power.
Status of Women
There was a drastic change in the position of women. They were not educated or allowed to read the Vedas. They no longer participated in the sabha. Child marriage and sati came into existence and widow remarriage was strongly opposed. The women were supposed to be under the control of her father and later her husband.
Caste System
The caste system developed gradually. The Aryans made the defeated dasas do unpleasant work. Division was created between the dasas and the fair-skinned Aryans. The dasas were given the name shudras and were not allowed to take part in any Aryan ceremony. Hence the caste system consisting of the four castes came into being-the brahmins, kshatriyas, vaishyas and the shudras. We will be learning more about the caste system in the later chapters.
Economic life
Agriculture became very important. Copper, bronze and iron implements were used. The main crops were wheat, rice and barley. Artisans2 produced better goods. Weaving was practiced on a wide scale mostly by women.
Religion
New gods were worshipped. Prajapati, the creator, was most important. He was later called Brahma. Shiva and Vishnu were also worshipped. Idol worship also began. Sacrifices were performed to please the gods who then blessed the people.
Thus, the Aryans brought with them their customs and ways of thinking and influenced the lives of the natives.
MEGALITHS
The word megalith comes from the Greek words megas and lithos meaning ‘great stone”. Megaliths are large slabs of stone used to mark the burial sites. Numerous megaliths have been found in Karnataka, Andhra Pradesh, Maharashtra, Kerala, Kashmir and the north- east.
In a megalithic burial, the bones of a dead person were placed in an urn. This urn was buried and surrounded by a circle of large vertical stones. A large horizontal stone formed the capstone.
If the pit burial has a circle of large stones, it is called a pit circle. If the pit had a heap of stones piled on top, it is called a cairn.
Unlike the Neolithic burials which were in the habitation area, megalithic burials were away from the occupation area. Grave goods like pottery, ornaments and weapons were also found. Pottery was of black and red variety. Weapons consisted of iron axes, spades and daggers. Ornaments were made of carnelian and gold. Some copper objects were also put in the grave. Sometimes horse skeletons and equipment were also found. The number of grave goods probably depended on the status of the person. The presence of these goods is indicative of their belief in afterlife. Some graves have skeletons of more than one person. This is suggestive that probably people from the same family were buried in the same place. The people who died later were got in through portholes.
Megaliths were built with great care and must have been an important part of the lives and beliefs of the people who constructed them.
INAMGAON
Inamgaon is a village in Pune district of Maharashtra. It is located near the River Ghod, a tributary of River Bhima. It is said to have been occupied from 1600 BCE to 700 BCE.
Houses here had fire pits. The pottery was fine, well-baked and designed. A pottery kiln has also been identified. There was an increase in farming and animal domestication. They cultivated grams, beans, peas and lentils apart from wheat, barley and rice. Fruits like berries and dates were also collected.
Bones of animals have been found. These bones have cut marks which are evidence that animals were also used for food.
The adult dead bodies were mostly buried away from the abitation site. Sometimes the burials were in the houses. The dead body was laid out straight, with the head towards the north. A number of burial goods including pots, ornaments and tools were also buried with the dead person. Multiple burials have also been found. In some graves, more than one skeleton and the absence of burial goods indicate that there was probably a large scale killing because of which burial goods were not enough for all the graves. In one large house which had a granary, one man was found buried in a cross legged position in a clay jar.
Q. Why do you think Inamgaon was located near a river?
Around the World
During the Shang Dynasty (1600-1046 BCE) in China, seers4 used bones or shells of tortoises for reading oracles5. They inscribed a question which they wanted to ask on the oracle bone. The bone was then heated. The cracks formed in the bone were studied and interpreted. Archaeologists have found thousands of oracle bones and shells in China. Oracle bones of the Shang Dynasty were ox scapulae and plastrons6 only. They had characters and holes drilled into them.
Palaeolithic: This term refers to the age where we find a large number of stone tools. It extends from 2 million years ago to about 12,000 years ago and is divided into Lower, Middle and Upper Palaeolithic.
Mesolithic: This period extends from 10,000 years ago to about 12,000 years ago. Stone tools found during this period were generally tiny and were called Microliths.
Neolithic: This was the period that dates back to about 10,000 years ago, and is, therefore, known as the New Stone Age.
The Earliest People: They were hunter-gatherers, a name derived from the way they collected food. They hunted animals, collected berries and fruits and gathered nuts, stalks and eggs. To hunt, they needed to move constantly, and to gather plant products, they needed knowledge about the edibility of plants and change of seasons.
Archaeological Evidence of Early Man: How do we know about the early man? This has been possible through an analysis of objects found, which were probably used by the early man. For example, tools made of stones, bones and wood.
Uses of Tools: Stone tools were used to cut meat and bones, scrape bark (from trees) and hides (animal skins) as well as to chop fruit and roots.
Making Stone Tools: Two different techniques were used for making stone tools.
Choosing a Place to Live In: Dwellings chosen by the early man were located near sources of water, such as rivers and lakes as well as where the good quality stone was available for their tools.
Painting-Rock paintings: Paintings on a rock shelter.
Finding out about Fire: At Kurnool caves in Andhra Pradesh, evidence and traces of ash have been found suggesting use of fire. The fire might have been used as a source of light, to cook meat and to scare away animals.
A Changing Environment: About 12,000 years ago, there was a major change in the climate of the world. This change led to a shift to warm conditions, leading to the development of grasslands at many places which helped people to start thinking about the herding and rearing animals.
Habitation-cum-Factory Sites: Places where stones were found and early people made their tools. Sometimes, people lived (habitat) here for a longer span of time.
Bhimbetka: This is a place in Madhya Pradesh where we find examples of habitation sites, natural caves and rock shelters.
People who lived in the subcontinent about 2 million years ago were Hunter-gatherers. They hunted wild animals and gathered plant produce to get their food. They moved from place to place, in search of more food, water and resources.
Hunter-gatherers made and used various types of tools—tools of stone, wood and bone
Habitation refers to the place where people lived.
Stone tools were made using different techniques like a stone on stone (using a stone to give required shape to another stone) and pressure flaking.
The fire was used by the early people. They used fire as a source of light, to cook meat and to scare away animals.
Grasslands developed in many areas due to change in climate around 12000 years ago. Herding, and rearing animals and fishing became common.
Several grain-bearing panes of grass, like wheat, barley, rice grew naturally in different parts of the subcontinent. The people also began growing plants on their own.
Many old caves have paintings on their walls. They show wild animals and are drawn with great accuracy and skill. A painting from a rock shelter.
In Hunsgi, a number of early Palaeolithic sites have been found. A large number of tools were also found, most of which were made of limestone.
Factory-Sites: Places where the stone was found and where people made tools are called Factory-sites.
Grasslands: Areas of land with high fertility and thus good for growing crops are called Grasslands.
Habitation-Cum-Factory Sites: Factory-sites, where people lived for some time, have been called Habitation-cum-factory sites.
Hunter-Gatherers: People who lived in the subcontinent about two million years ago and who hunted wild animals, caught fish and birds, gathered food to eat, were the Hunter-gatherers.
Palaeolithic: The part of history extending from 2 million years ago to about 12,000 years ago is called the Palaeolithic period.
Mesolithic: The part of history extending from about 12,000 years ago to about 10,000 years ago is called the Mesolithic period.
Microliths: Stone tools of the Mesolithic period are called Microliths.
There are several things we can know about our past such as:
What people used to eat, the type of clothes they used to wear, the houses in which they lived.
How were the lives of hunters, herders, farmers, rulers, merchants, priests, crafts persons, artists, musicians, and scientists?
The games children used to play, the stories they have heard, the songs they sang.
Where did people live?
People have lived along the banks of the Narmada river for several hundred thousand years. These people stayed on the bank of Narmada river as they knew about the vast wealth of plants in the surrounding forests. They used to collect roots, fruits and other forest produce for their food. Sometimes they also hunted animals.
The areas where women and men first began to grow crops such as wheat and barley was about 8000 years ago.
People also began to look after animals like sheep, goat, and cattle and used to live in villages.
The places where rice was first grown are to the north of the Vindhyas.
About 2500 years ago, cities developed on the banks of the Ganga and its tributaries, and along the sea coasts.
In ancient times, the area along the Ganga and its tributary rivers, to the south of the Ganga was known as Magadha which is now lying in the state of Bihar. Men and women moved in search of livelihood and also to escape from natural disasters like floods or droughts. These movements of people enriched our cultural traditions. People have shared new ways of carving stone, composing music, and even cooking food over several hundreds of years.
Names of the land
Our country is known by both words i.e India and Bharat.
The word India comes from the Indus, called Sindhu in Sanskrit. The Iranians and the Greeks who came through the northwest about 2500 years ago called it the Hindos or the Indos, and the land to the east of the river was called India.
The name Bharata was used for a group of people who lived in the northwest, and who are mentioned in the Rigveda, the earliest composition in Sanskrit (dated to about 3500 years ago). Later it was used for the country.
Finding out about the past
One way through which we can find out about our past is by reading the books that were written long ago. These books are called manuscripts because they were written by hand. These were written on palm leaves, or on the specially prepared bark of a tree known as the birch, which grows in the Himalayas. These books dealt with all kinds of subjects: religious beliefs and practices, the lives of kings, medicine and science. Besides, there were epics, poems, plays as well.
Inscriptions
Inscriptions are writings on relatively hard surfaces such as stone or metal. In the past, when kings wanted their orders inscribed so that people could see, read and obey them, they used inscriptions for this purpose. There are other kinds of inscriptions as well, where men and women (including kings and queens) recorded what they did. For example, records of victories in battle.
Archaeologists
An archaeologist is a person who studies the remains of buildings made of stone and brick, paintings and sculpture. They also explore and excavate to find tools, weapons, pots, pans, ornaments and coins. They also look for bones of animals, birds, and fish to find out what people ate in the past.
Historians use the word source to refer to the information found from manuscripts, inscriptions and archaeology. Once sources are found, learning about the past becomes an adventure. So historians and archaeologists are like detectives, who use all these sources like clues to find out about our pasts.
One past or many?
The title of this book is Our Pasts – I. The word ‘pasts’ in plural is used to draw attention to the fact that the past was different for different groups of people. For example, the lives of herders or farmers were different from those of kings and queens, the lives of merchants were different from those of crafts persons, and so on. It is even true today as people followed different practices and customs in different parts of the country.
Archaeology did not help us to know more about the ordinary people in the past because they did not keep records of what they did. Whereas, kings used to keep the records of their victories and the battles they fought.
What do dates mean?
The years are counted from the date to the birth of Jesus Christ, the founder of Christianity. All dates before the birth of Christ are counted backwards and usually have the letters BC (Before Christ) added on. In this book, we will refer to dates going back from the present, using 2000 as our starting point. 2000 means 2000 years after the birth of Christ.
The name atom comes from the Greek word ‘atomos’, which means uncuttable or indivisible.
An atom is the smallest particle of an element having the same chemical properties of the element.Atoms are the basis for everything in the universe, including us.
Atoms are tiny particles that are too small to see, even with a microscope. They are so tiny that if people were the same size as atoms, the entire population of the world would fit into a small box.
Just like letters are the basic building blocks of any language, atoms are the primary building blocks for things around us. The chair you sit on, the lunch box you carry to school, pizza you eat – just everything is made up of atoms.
When atoms combine together they form molecules.
Let us study about the atoms and molecules in detail.
Dalton’s Atomic Theory:
Matter is made of atoms which cannot be broken down further.
Atoms cannot be created or destroyed in a chemical reaction.
Atoms of the same element are identical to each other while atoms of different elements differ in mass and chemical properties.
Atoms combine in definite ratios of whole numbers to form compounds.
The number and composition of atoms are constant for a given compound.
A few important definitions
Atom: Atom is the smallest unit of matter and is further made up of protons, neutrons, and electrons. Atomic radius is measured in nanometres (10−910−9 m)
Atomic mass: A mass unit equal exactly to 112th112th the mass of one atom of Carbon-12
Gram atomic mass: The atomic mass of an element expressed in grams is called gram atomic mass
Molecule: The smallest unit of an element or a compound which can exist independently and show all its physical and chemical properties is called molecule. A molecule may have atoms of the same kind(element) or of different kinds (compound)
We come across many chemical substances and compounds daily. Everything around us consists of chemical substances. These may be man-made chemical substances and substances extracted from nature
Examples of chemical products at home are dishwashing and cleaning detergents, glue, common salt, baking soda, etc
These chemicals are made up of atoms of a fixed proportion and these atoms are arranged in a certain way. In order to find out what these proportions are and how they are arranged for any given substance, we need to know the chemical formula of the substance or compound.
In order to make it easier to describe elements and molecules, chemical formulae are used. They are used to describe the number of atoms in each element or compound. It contains the symbols of the atoms of the elements present in the compound, as well as how many there are for each element in the form of subscripts.
For example, ‘H’ represents one atom of hydrogen and ‘O’ represents one atom of oxygen. If we want to represent two atoms of hydrogen, instead of writing H H, we write H2. The subscript “2” means that two atoms of the element hydrogen have joined together to form a molecule.
We will study about the formulae in this chapter.
Importance of chemical formulae:
It tells us about the types of elements present in the compound
It tells us the number of atoms of each kind present in the molecule of the compound
It gives us the mass of one molecule of the compound
Chemical Formulae
Every chemical substance is known by a specific name.
Each chemical compound is represented by a chemical formula that gives its composition (constituent elements present) and the number of elements of each type present.
Molecular Formula
A chemical formula that represents the composition of a molecule of the substance in terms of the symbols of the elements present in the molecule is also called molecular formula.
For example, the molecular formula of water is H2O, which means that one molecule of water contains two atoms of hydrogen and one atom of oxygen.
Significance of Molecular Formula
It represents name of the substance
It represents one molecule of substance
It gives the names of all the elements present in one molecule of the substance. It also gives the number of atoms of each element present.
It represents a definite mass and refers to the presence of 6.023 x 1023 molecules (known as the mole concept).
Ancient people like the Greeks, Romans, Indians, the Chinese, knew about elements like iron, copper, gold, silver, lead etc. The first element humans knew was most probably the carbon, in the form of charcoal.
There are about 115 elements out of which there are 92 elements that occur naturally. Most of them were discovered by the late 1800’s.
The modern arrangement of the elements is known as the Periodic Table of Elements and is arranged according to the atomic number of elements. The scientist Dmitri Mendeleev, a Russian chemist, proposed an arrangement of know elements based on their atomic mass.
The periodictable of the chemical elements is a tabular display of the known chemical elements. Each element is listed by its atomic number and chemical symbol.
Symbols are used to represent elements. A symbol is a letter or picture used to represent something. One or two letters are used to represent elements. Example: The symbol for aluminum is Al and the symbol for oxygen is O.
A chemical formula is used as a quick way to show the composition of compounds. Letters, numbers, and symbols are used to represent elements and the number of elements in each compound.
Let us study in detail about elements, compounds, symbols, and formulae in this chapter.
Substances
Substances:
Substances are classified into two types.
Pure Substances – A substance which is made of one kind of particle.
Examples – iron, gold
Impure substances or Mixtures – A substance which contains two or more different particles is known as a mixture.
Example: a salt solution is made up of two components, salt, and water.
On the basis of their chemical composition, pure substances are classified as elements and compounds.
Elements :
A pure substance which is made up of only one kind of atom and cannot be broken into two or more simpler substances by physical or chemical means is referred to as an element. Example: Zinc, Sulphur.
Characteristics of elements:
An element is homogeneous in nature; it is a pure substance, made up of only one kind of atoms. For example, iron and silver are made of only iron and silver atoms.
An element cannot be broken down into simpler substances by any physical or chemical methods such as heat, light electricity, or chemical reactions with other substances. For example, if you were to smash a piece of iron into smaller pieces or heat it, the piece still remains as the element iron.
An atom is the smallest unit that shows all the properties of an element. For example, an atom of iron shows all the properties of that metal.
Elements have sharp melting and boiling points.
Symbols to represent elements:
Each element is represented by a symbol. It is usually derived from the first letter of its name in English or Latin. The first letter of the symbol is always in upper case. Some elements are represented by the starting alphabet of its name. Example: Carbon is represented as C. Symbols of some elements are the first two alphabets, where the second alphabet is in the lower case. Example: Sodium is represented as Na, where Natrium is the Latin name of sodium.
Compounds:
They are made up of one or more elements and are denoted by chemical formulae.
A compound contains atoms of different elements chemically combined in a fixed ratio.The smallest unit of a compound is a molecule
Compounds contain different elements in a fixed ratio arranged in a defined manner through chemical bonds.
A compound can be broken down into simpler substances by chemical methods/reactions
A compound is represented using a formula. Example: Water (H2O), Sodium chloride (NaCl),Magnesium oxide (MgO)
Water is one of the essential element for life on earth. Most of the earth’s surface is covered with water. Any guesses on how much fraction of the earth is covered with water?
About three-fourth of earth’s surface is covered with water.
An interesting fact for you to know is that most part of the human body consists of water.
We need water in daily life for different purposes: drinking, washing clothes and utensils, cooking, watering plants to name a few. As already stated most of the earth’s surface contains water, yet all of it can not be utilised. So how and from where do we get water for daily use?
In this chapter, you will learn about sources of water, different states of water, water cycle, the importance of water, water-borne diseases, and finally purification of water.
Sources of water
Most of the earth’s surface is covered by the oceans.
Sea is the largest source of natural water, but it contains a high amount of dissolved salt and cannot be used directly for irrigation or drinking.
Rivers and lakes contain water that comes from glaciers or rainfall. As rivers flow downhill and through plains, they collect many substances like minerals, organic matter, clay. Sometimes bacteria may also be present in river water.
We meet all our domestic and industrial requirements of water from rivers.
Ground water is a pure form of water because it has no suspended impurities or germs. However, it may have dissolved minerals which give it a distinct taste and even medicinal properties.
We can obtain ground water by digging wells.
Rainwater is the purest form of water.
It will contain dissolved substances like dust, carbon dioxide, oxygen and nitrogen.
States of water
Water exists in all three states of matter: solid, liquid and gas.
Ice, water and steam have different physical properties but same chemical properties.
The interconversion of these three states of water also occurs in nature and it is called the water cycle.
Water cycle
Evaporation:
Heat from the Sun causes water on Earth (in oceans, lakes etc.) to evaporate (turn from the liquid into the gas) and rise into the sky. This water vapour collects in the sky in the form of clouds.
Condensation:
As water vapour in the clouds cools down it becomes water again, this process is called condensation.
Precipitation:
Water falls from the sky in the form of rain, snow, hail, or sleet, this process is called precipitation.
Collection:
Oceans and lakes collect water that has fallen. Water evaporates into the sky again and the cycle continues.
Importance of water
Commercial water use includes fresh water for motels, hotels, restaurants, office buildings, other commercial facilities, and civilian and military institutions. Domestic water use is probably the most important daily use of water for most people.
Domestic use includes water that is used in the home every day, including water for normal household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens.
Industrial water use is a valuable resource to the nation's industries for such purposes as processing, cleaning, transportation, dilution, and cooling in manufacturing facilities. Major water-using industries include steel, chemical, paper, and petroleum refining. Industries often reuse the same water over and over for more than one purpose.
Irrigation water use is water artificially applied to farm, orchard, pasture, and horticultural crops, as well as water used to irrigate pastures, for frost and freeze protection, chemical application, crop cooling, harvesting, and for the leaching of salts from the crop root zone.
Nonagricultural activities include self-supplied water to irrigate public and private golf courses, parks.
Potable water:
Potable water is required for human consumption (drinking). It must be:
Clean and transparent.
Free of germs and suspended impurities.
It should contain some amount of gases and minerals so that it does not taste flat.
It should not have harmful chemicals.
Waterborne diseases
Drinking dirty or contaminated water causes water borne diseases.
Some waterborne diseases are:
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Purification of water
Water must be treated or purified to make it fit for human consumption.
Coagulation stage:
Alum and other chemicals are added to the water at this stage.
Suspended particles get stuck to the chemicals to form 'floc'.
Sedimentation Stage:
As particles get stuck they become heavy and sink to the bottom of the chamber.
At this stage, most of the particles are stuck to form sediments, sinking to the bottom.
The water is passed onto the Filtration chamber.
Filtration stage:
As water passes slowly through this chamber, finer particles (sediments) are filtered out over layers of sand, charcoal and gravel.
Disinfection stage:
Chlorination or addition of chlorine to water is used to kill any bacteria and other living organisms that may be in the water.
It is very normal and natural for fresh water to contain living organisms.
Ozonization:
Because of its excellent disinfection and oxidation qualities, ozone is widely used for drinking water treatment.
Ozone can be added at several points throughout the treatment system,
Storage stage:
The water is then passed into large storage tanks and left for a while for the action of disinfection to be complete.
At the tail end of this storage tanks, huge pipes are connected to transport water to our homes and workplaces.
At home, the easiest way to sterilise water is by boiling. Boiling water kills germs and makes it safe for drinking.
Filtering through a cloth also removes soil and other large particles.
Chlorine can be added to overhead tanks to disinfect water.
Apart from this, we can also install RO systems or water purifiers with activated carbon filters to purify water.
Any liquid in which a solid dissolves easily is known as a solvent. Water has this excellent property of dissolving many substances.
Can you name one or two substances which you use every day, which easily dissolves in water?
They are the salt and the sugar.
Similarly, there are many other substances which dissolve in water. Hence, the name universal solvent for the water. In this chapter, you will learn more about water as a solvent and you will also learn step-by-step procedure to prove that tap water and sea water contain dissolved solids and gases.
Water has the ability to dissolve many substances in it. However, water dissolves different amounts of different substances under the same conditions. For e.g., for the same volume of water, we can dissolve more sugar than salt.
Aquatic life depends on the oxygen dissolved in water.
Stirring and heating increase solubility of a substance.
Pure water is transparent, colourless, tasteless and odourless.
Temperature and solubility:
Add a 1/2 cup of lukewarm tap water to a plastic cup.
Weigh about 5 tablespoons of salt and gradually add the salt to the tap water, stirring to mix.
Stop adding salt when it no longer dissolves.
Repeat the mixing steps with 1/2 cup each of ice water and hot water; determine at which temperature more salt dissolves.
This experiment proves that the solubility of some substances is dependent on temperature, and we observe that much more salt dissolves in hot water than in cold.
Experiment to show that tap water and sea water contain dissolved solids and gases
Two round bottom flasks are filled with tap water and sea water respectively and heated. Bubbles of gas will be released from the water and travel into the test-tube. Continue until the contents of the flask are boiling.
About half a test-tube full of gas will be collected in each case, all of which has been displaced from solution by heating.
A glowing splint continues to glow and does not immediately go out when placed in the gas.
If both samples of water are placed in an evaporating dish and allowed to evaporate, the water completely evaporates leaving behind traces of solids in the dish, showing that the samples of water contain dissolved solids.
Water plays a very important role for all of us in daily lives. You might postpone eating food, but you definitely need water to quench your thirst. Even though most of the earth’s surface is covered with water, most of it is unusable.
Have you tasted sea water?
In case you have, it is very salty, right?
So, one of the main sources of water is rain. Rainwater is collected in rivers, tanks, reservoirs which are available for use by all living beings. It is essential to conserve water and make sure that the water is not polluted by industrial waste or any such means, water is not wasted and so on. It is the responsibility of all of us to preserve and conserve water for generations to come. In this chapter, you will learn about the importance of water, water conservation, water pollution and preventing water pollution.
Water is a precious natural resource and we must conserve water.
We can conserve water by using it in a wise manner.
97% of all the water on the earth is salt water, which is not suitable for drinking. Only 3% of all the water is fresh water, and only 1% is available for drinking. That is why we must conserve water.
A few simple ways to reduce usage and wastage of water:
Turn off the tap when you brush your teeth.
Fix a dripping tap and leaking pipes.
Use a bucket instead of the shower.
Water your garden with a watering can rather than a hosepipe.
Rainwater harvesting is used by many people to save and use rainwater.
Use drip irrigation on fields.
Grow more trees to maintain water cycle.
Avoid water pollution.
Build dams to store and conserve water.
Water pollution:
Sewage, kitchen and industrial wastes are dumped into the water.
Chemicals from farms (dissolved fertilisers) and acidic waters from mines and industries pollute the water.
Nuclear and thermal power plants use water for cooling purposes and discharge the hot water into seas and rivers. This causes an increase in temperature of the water and kills fish and plants in the water.
Water pollution can be controlled by:
Treatment of sewage before being released into rivers.
Removal of solid waste and garbage from sewage.
Avoid using detergents, fertilisers, plastics and pesticides which can increase the chemical content of the water.
Treat all effluents from factories to make them harmless.
Avoid using lakes, ponds and rivers for bathing, washing animals and defecating and for disposing of dead bodies.
Anything which occupies space and has mass is called “Matter”. Eg. Oxygen, air, silver, steel
Characteristics of matter: Things around us are composed of different kinds of materials. In the same material same type of molecules are found such as in case of ice, water molecules are present. (1)Matter occupies the space: The volume is the amount of space occupied by the material. (2) Matter has mass: Any kind of material visible and invisible, has certain amount of matter in it called as “mass” Structure and composition of matter: Matter is made up of very very small particles in it. These particles which make up the matter are atoms, ions and molecules . • Atoms : Atoms consist of nucleus which is positive charge at centre and electrons which possesses negative charge as in cloud around it. In case of sodium and helium they presence in combine form as lack of individual existence to form molecules. • Molecules: These are the smallest distinct units into which a pure matter can be divided. They represent the chemical and composition property of matter. Combination of two or more atoms result in formation of molecule. Combine atoms may be of one kind or different. Water is made up of hydrogen and oxygen where hydrogen molecule is made up of two hydrogen atoms. • Ions: Ions may be positive or negative with respect to atoms or group of atoms. Atom or group of atom transformed to form ions when they lose or gain the one or more electron. Eg. Sodium ion (Na+ ) , Chlorine ion (Cl- )
States of matter:
On the basis of physical property namely temperature the matter is classified into (A)Solid -ice (B)Liquid- water (C)Gas- air By changing the temperature one can easily change the states of matter. The characteristic of matter is depend upon the arrangement of atoms or molecules inside the matter. The molecules of matter are held together by force of attraction between them, called as intermolecular force of attraction. And the space between molecules are called as intermolecular space. These arrangement of particles inside the matter decides whether is exist as solid , liquid or gas.
Solid states: Characteristic by structural rigidity and with definite shape and volume. Molecules are tightly packed due to strong intermolecular force in between solid particles .
Properties of solid :
Have tightly packed particle
Possess fixed shape and fixed volume
Solid do not show fluidity
Cannot be compressed much Liquid state: Characterised by the change in its shape but resistivity towards change in its volume. They are less tightly packed as compared to solid. Within the liquid molecules are moving one position to another, indicating fluidity. Properties of liquid:
Have loosely packed particles.
Have fixed volume but do not have fixed shape , take the shape of container in which they are place
Liquid flow easily.
Liquid cannot be compressed much
Gaseous state: State of matter which characteristic by its capacity to change its shape and size. They are very loosely packed as compare with solid and liquid arrangement of molecules. They do possess weak intermolecular forces which result in molecules are far apart. They are free to move.
Properties of gases:
Particle within the gas , are loosely packed.
They take the whole shape and volume of the container in which they are kept as result of neither of fixed volume nor a fixed shape.
Gases easily flow.
Gases can be compressed with ease into small volumes. Effect of arrangement on the basis of their property: The property shown by matter is depend upon the arrangement present in it. o SOLID: In solid structure the molecules are closely packed, in such way that their position is almost fixed. Hence retained shape and volume. The intermolecular space is very small as the result of greater intermolecular force of attraction between solid particles. Application of heat onto solid, brings the extra energy to molecules and they begin to move apart from their position finally resulting in the state change from solid to liquid. o LIQUID: Intermolecular space in the liquid particle is more comparable to solid as result of which due to the weaker intermolecular force. That’s why the molecules are free to move. Hence liquid does not possess definite shape and it takes the shape of container. On heating liquid changes into vapour which is gaseous state. This is because on heating liquid molecules get or acquires energy and start moving with higher speed and near the surface or boundary get escape from the liquid and produce vapour. o GASES: Characteristic by fast moving particle with average speed of 1600km/hr. The intermolecular space is wide because of very weak intermolecular force of attraction between gas molecules. The molecular force of attraction is depend upon the density but due to low density the force is non-existence. Hence gas neither has shape nor have fixed volume. On cooling the density goes on increase result into establishment of intermolecular force which brings molecule closer and gas get converted into liquid
Do you know you use a lot of machines every day without even knowing about it? Remember those scissors that you used to cut paper for your art class? And the stapler that you used to staple extra sheets together? They are all simple machines.
Every day you use machines without even thinking about it. A machine is anything that helps make work easier. Basic tools like staplers, screwdrivers and scissors are simple machines. These machines are all based on simple inventions like levers, planes, pulleys or wheels.
Why do we need machines?
With the help of machines, a small force can be used to overcome a large force. For example, a screw jack is used to lift an object as heavy as a car to change its tyres.
We need machines to:
Lift heavy loads with a small effort.
Carry out unsafe and dangerous tasks.
To increase the speed of a moving object.
To move, lift or perform an action in the required direction.
To reduce the risk in performing hazardous tasks.
Simple Machines
Simple Machine:
A machine is a device that helps us to do work with less effort in less time. A simple machine has few or no moving parts.
Simple machines are basically classified into two groups, levers and inclined planes.
Simple machines like the pulley, screw, wheel and axle and wedge come under these two categories.
The see-saw in the playground is a simple machine.
You can use these simple machines to build a complex machine. For example, a bicycle is a complex machine that is made using of nearly every kind of simple machine.
Pulley
A pulley is a flat circular disc having a groove in its edge and capable of rotating around a fixed point passing through its central axis, called an axle.
The two commonly used types of pulleys are single fixed pulley system and the single movable pulley system.
Single Fixed Pulley System:
A single fixed pulley system or a simple pulley consists of a grooved wheel, made of wood or metal, with a rope passing through it.
The pulley rotates about an axle passing through its centre.
The axle is fixed to a frame or a block.
The pulley is normally fixed to a support above the load.
The load is tied to one end of the rope and the effort is applied at the other end.
Such a pulley makes our work easier by simply changing the direction of the force, i.e. a load is lifted up using a downward effort. It is easier to lift a load up by pulling it down rather than by pulling it up directly.
Note that a simple pulley does not reduce the effort required to lift a load.
A simple pulley is used to hoist a flag, to draw water from a well, etc.
Single Movable Pulley System
This pulley system has a block of two pulleys.
In this system, a load of W kgf can be lifted with an effort of W/2 kgf only.
In a block and tackle arrangement, the pulleys are assembled together to form blocks and then blocks are paired so that one is fixed and the other moves with the load.
The rope is threaded, or reeved, through the pulleys to provide a mechanical advantage that amplifies the effort applied to the rope.
An example of a practical application of pulleys and levers working together is the crane which is used to lift heavy loads.
The Wheel and Axle
Wheel and axle essentially consist of two cylinders of different radii joined together, such that if one is made to rotate the other also rotates. The cylinder with the larger radius is called the wheel and that with a smaller radius is called the axle.
Examples of wheel and axle system are a doorknob, a knob of water tap, a screwdriver, egg beater, a hand drill, etc.
Inclined Plane
An inclined plane is any sloping flat surface along which a load can be pushed or pulled with less effort. A hospital ramp on which a wheelchair can be pushed easily, a wooden plank used to load heavy boxes into the rear of a truck, winding roads around a hill, winding staircases, etc. are all inclined planes.
Wedge
If two inclined planes are put together to form a sharp edge, it is called a wedge. So a wedge is a double inclined plane. It works on the principle of inclined planes.
A wedge is used to tear apart or cut through objects. Knives, needles, axes, chisel, etc. are examples of a wedge.
Screw
A screw is a rod or nail with grooves on its circular curved surface and is used to hold two objects firmly together.
In simple terms, a rotating (winding) inclined plane is called a screw. The winding edge of a screw is called a thread. The grooved part of the screw is an inclined plane.
The head of the screw has a groove for the tip of a screwdriver. When the screw is held against a wooden block and its head is turned using a screwdriver, the tip of the screw moves into the wood. Because of the grooves, a screw holds the wood more firmly than a nail. Also, less force is required to insert a screw into wood than a nail because of the inclined edge.
Uses of Screws
Screws are used to join two pieces of wood or metal. As the screw is a winding inclined plane, it cannot be pulled out easily from the attached pieces.
A nut and bolt arrangement has two winding inclined planes. One inclined plane is on the external side of a metal cylinder and is called the bolt. The other inclined plane is on the inner side of a hollow metal cylinder and is called the nut. When the nut is given a circular motion over the bolt, it moves up or down without slipping and can withstand a lot of load.
A cork screw is used for pulling out the cork from the bottles of ketchup or wine.
The screw jack used to lift automobiles for repairs works on the principle of a screw.
Maintenance and Care of Machines
The following points should be remembered about the maintenance of machines.
Machines should be protected from dust to prevent their wear and tear. So when not in use, machines should be kept covered.
To avoid rusting due to exposure to moisture, the non-movable iron parts of a machine should be painted.
To reduce friction, the moving parts of a machine should be regularly lubricated.
Example
Why do we have three types of levers?
A rigid bar resting on a pivot that is used to move a heavy or firmly fixed load with one end when pressure is applied to the other is called alever. For example, imagine the incline in your parking lot that will take to your parking space in the garage.
Depending on the location of the load, the fulcrum, and the force levers are classified into three classes. They are:
First class lever: It has a fulcrum between the force and the load, like a crowbar.
Second class lever: It has a load between the fulcrum and the force, like a wheelbarrow.
Third class lever: This lever has the force between the fulcrum and the load, like the arm on a human.
Have you ever wondered why refrigerator magnets stick to the refrigerator door easily?
Magnets stick to the refrigerator door because, beneath the paint, the door is made of steel. A magnet is attracted to steel and hence sticks to the door.
A long time ago ancient people knew about the rocks that attracted metals. They were called lodestones.
The Greeks were the first to discover the phenomenon of magnetism about 4000 thousand years ago. A Greek shepherd named Magnes discovered a natural magnetic rock. This rock which had a compound of iron called magnetite was able to attract metals.
Ancient Chinese and Indians also knew about magnets.
In this chapter, you will learn about magnets, types and features of a magnet You will also learn about the properties and uses of magnets.
Magnetic Materials
Magnetic materials are those that are attracted by a magnet.
Examples: Steel, iron etc.
Non-Magnetic Materials
Non-magnetic materials are those that are not attracted by magnets. Do you know why the coins that we use are not attracted by a magnet? That s because, various metals are mixed together to make coins that are non-magnetic.
Examples: Paper, leather etc.
Magnetic Poles
Magnetic poles are the tips of a magnet and contain the highest magnetic strength. When a magnet is freely suspended, the tips point towards the north and south.
The tip pointing towards the geographical south is known as its south pole. The tip pointing towards the geographical north is known as the north pole.
Types of Magnets
Magnets are of the following two types, natural magnets and artificial magnets.
A natural magnet is a naturally occurring substance with magnetic properties. Example: Magnetite.
An artificial magnet is a substance into which magnetic properties are artificially induced.
Examples: Magnets made of iron, cobalt, nickel etc.
Artificial magnets can come in various shapes such as a dumb-bell shaped magnet, bar magnet, U-shaped magnet, cylindrical magnet, magnetic needle, etc.
Artificial magnets are beneficial compared to natural magnets as they can be made in any desired shape.
In addition to this, artificial magnets can be made very powerful that is not possible with natural magnets.
Magnets made of an alloy that consists of aluminium, nickel, and cobalt (ALNICO) added to iron are the strongest magnets.
Magnets also classified as temporary or permanent based on their capacity to retain magnetism.
Temporary magnets are those magnets which cannot retain their magnetism for a long time.
Examples: Pure iron (Soft iron) and electromagnets that are made by passing an electric current through an iron piece.
Permanent magnets are those magnets which retain their magnetism long after removal of the magnetising force.
Example: Magnets made from steel (carbon + pureiron).
Uses of a magnet:
Magnets can be made into different size, shape and strength, based on their use. Devices such as TVs, loudspeakers, radios, telephones etc. make use of magnets.
Properties of Magnets
A magnet attracts other magnetic material towards itself.
Like poles repel each other. and unlike poles attract each other.
A freely suspended bar magnet always aligns in the north-south direction.
When a bar magnet is rubbed on an iron bar, the iron bar is converted into a magnet.
There is no magnet with a single pole. Even when a magnet is cut into two pieces, each piece will behave as an independent magnet, with two poles, a north pole and a south pole.
Compass
Have you seen a compass? There must be one in the physics lab of your school. Most smartphones also have a compass. Ask your parent or neighbour to show you how the compass works.
As the needle in a traditional compass always points in the direction of the north, it is easy to find other directions easily. Let us see how the compass works.
A compass is an instrument with a thin magnetic needle supported from a pivot.
There is a round dial on the outer edge of the compass that marks the directions of North, South, East and West.
The needle is positioned on a dial with marked directions.
The north pole of the magnetic needle is painted with red colour.
The magnetic needle in the compass always points towards the north-south direction.
With the proper alignment of the dial, the directions can be found.
An airtight box contains the entire assembly.
In the olden days, an old pointing device namely the south-pointing fish was used to find the directions. In this instrument, the fish head was pointed towards the south.
Storage of Magnets
A magnet gets demagnetised when left by itself for a long period of time. In other words, the magnet loses its magnetic property. This can be avoided by storing them between soft iron pieces also known as keepers when a magnet is not used. The Arrangement of bar magnets in pairs such that the opposite poles face each other and keeping two soft iron pieces at the two tips of the pair of magnets avoids demagnetisation of bar magnets.
How to Protect Magnets from Losing Their Magnetic Properties
Do not:
Drop magnets from a height.
Heat a magnet.
Hammer a magnet.
Keep certain items such as DVD’s, debit cards, CD’s, audio and video cassettes, credit cards or ATM cards, and mobile phones which contain magnetic material, away from magnets to prevent damage.
Uses of Magnets
Magnets are used in:
In stickers, magnetic toys, refrigerator doors, etc.
Making magnetic compasses that help sailors and navigators to know directions.
For separating iron from ores containing other non-magnetic substances.
Removing tiny iron pieces that have accidentally fallen into the patient’s eye by eye doctors.
Electromagnets are used in:
Generators, motors, loudspeakers, telephones, TV sets, fans, mixers, electric bells, etc.
Cranes to lift heavy iron bars and to separate iron objects from scrap.
