Light, Shadow and Reflection
Light is a form of energy visible to the human eye that is radiated by moving charged particles. Speed of light in air is about 3 x m/s.
Ray: It is a very narrow and straight path of light.
Beam: It is broader and consists of several rays.
Sources of Light
The objects which give out light are called sources of light. Sun, star, bulb, torch, candle lantern, lamp, etc. are the sources of light.
Luminous and Non-luminous Objects
The objects which produce their own light are called luminous objects. Sun, stars, bulb, torch, candle, lantern, lamp etc. are luminous objects.
The objects which do not produce light on their own are called non-luminous objects. Table, fan, book, chair, etc. are non-luminous objects.
Transparent, Translucent and Opaque Objects
Transparent Objects: The objects which allow light to pass through them. For example glass, water, air, etc.
Translucent Objects: The objects which allow light to pass through them partially. For example, oiled paper, tissue paper, muddy water, ground glass, etc.
Opaque Objects: The objects which do not allow light to pass through them. For example, wall, blackboard, metal sheet, etc.
If an object is placed in front of a source of light, the object cast its shade which known as shadow. All the opaque objects produce their shadow on the opposite side to the source of light. The shape of shadow depends on the followings:
Shape of the object
Size of the source of light
Position of the source of light
Reflection of Light
When a ray of light falls on the surface of a mirror, they are sent back. This phenomenon is known as reflection of light.
The ray which falls on the surface of a mirror is called an incident ray. The ray which is sent back after reflection is called reflected ray.
A spherical mirror is a mirror which has the shape of a piece cut out of a spherical surface. There are two types of spherical mirrors: concave and convex.
Reflecting surface of a concave mirror bulges inward whereas reflecting surface of a convex mirror bulges outward.
The images which are inverted and can be taken on the screen are called real images
The images which are erect and cannot be taken on the screen are called virtual images.
Food is a substance eaten by the living organisms in order to remain alive. Fruits, vegetables, eggs, meat, milk, etc. are the examples of food.
Sources of Food
Plants: Foods like cereals, pulses, fruits, vegetables, etc. are obtained from the plants.
Animals: Food like meat, milk, eggs, honey, etc. are obtained from animals.
Producers and Consumers
All living organisms has been broadly classified into two groups: producers and consumers.
Producers: All the green plants make their own food, therefore, green plants are called producers.
Consumers: Animals consume the food prepared by green plants, therefore, animals are called consumers.
Types of Consumers
Consumers have been classified in the following groups on the basis of their food habits:
The animals that eat only plants or plant products, are called herbivores. Cow, buffalo, goat, elephant, horse, rabbit, camel, etc. are the examples of herbivores animals.
The animals that eat only other animals are called carnivores. Tiger, lion, cheetah, wolf, snake, etc. are the examples of omnivores animals.
The animals that eat both plants and animals are called omnivores. Man, bear, dog, crow etc. are the examples of omnivores animals.
The animals that eat dead and decaying bodies of other animals are called scavengers. Vulture, hyena, etc. are the examples of scavengers.
These are organisms such as bacteria and fungi that break down the dead remains of plants and animals.
The animals that live in or on the other animals for their survival are called parasites. For example, mosquitoes, flees, leeches, etc.
Components of Food
The food that we eat is composed of carbohydrates, fats, proteins, vitamins, minerals, water, and roughage.
Functions and Sources of different components of food are given below:
Fibre to Fabric
Fibre to Fabric
We use clothes for making variety of things like shirts, pants, skirts, sarees, uniforms, bed sheets, blankets, curtains, table cloths, towels, school bags, gunny bags, etc. So clothes are very important for us. In this chapter we will study about different types of fibres.
Clothes: Clothes are fabrics which are made up of yarns and in turn yarns are made up of fibres.
Fibres: Fibres are very thin, thread-like strand from which clothes are made up of.
Yarns: Yarns are made up of fibres. Fibres are turned into long twisted thread by the process of spinning called yarns.
Fabrics: Yarns are woven together to make fabrics. Then fabrics are used to prepare different types of clothes like shirts, pants, bags, etc.
Types of Fibres
There are two types of fibres: natural fibres and synthetic fibres.
The fibres which are obtained from natural sources are called natural fibres. Cotton, wool, silk, flax, and jute are the examples of natural fibres.
We obtain cotton fibres from cotton plants. Seeds of cotton plants are covered with white, soft cotton fibres. Cotton fibres are separated from seeds by hands or machines.
The preparation of clothes or fabrics from cotton wools or cotton fibres involves mainly three processes which are as follows:
Ginning: The process of separating cotton wool from the cotton seeds is called ginning.
Spinning: The cotton fibres from cotton wool are drawn out and twisted to make yarns. This process is called spinning.
Weaving: In the process of weaving two distinct sets of yarns are interlaced at right angles to form a cloth. Cotton is mainly used to make clothes as it is soft and comfortable to wear. Cotton clothes let air in and can absorb sweat, therefore, very useful specially in and humid weather.
Wool fibres are obtained from the hair of animals like sheep, goat, rabbit, yak and camel. Wool cut off from the sheep with a thin layer of skin. The process is known as shearing. After shearing the wool is sent to the mills. Where it is cleaned, combed and spun to make fibre is then woven or knitted to make wool clothes. Wool is used for knitting sweaters, shawls and other wool clothes. Wool is a fluffy material and can retain air inside it, therefore, woolen clothes are very useful in winter season.
Silk fibres are obtained from silk worms. Caterpillars of silkworms cover them self from silk fibres called cocoon. The cocoon is boiled in water to separate the silk fibres from the silkworms. The process is known as reeling. Further the obtained silk fibres twisted to obtains silk yarns then silk yarns are woven to make silk clothes.
The earing of silkworm for the production of silk fibres is called sericulture.
Jute fibres are obtained from the stem of jute plants. Jute plants more...
Grouping Materials and their Separation
Sorting Materials into Groups
All the objects that we see around us are made up of matter called materials. Like, animals, insects, birds, plants, trees, houses, machines, tools, tables, chairs, clothes, etc. are objects which are made up of matter.
To understand the process of classification, first we have to know the basis of classification.
Basis of Classification
The characteristics or properties, which are taken as the base for the classification of given objects, are called basis of classification. There are a number of characteristics which are taken as the basis for classification. Like 'living and non-living', 'natural and artificial', 'solid, liquid and gas', 'shape', 'colour', etc.
Note: You can also classify the materials by selecting the characteristics as per your own choice.
Properties of Matter
Now let us understand some properties of matter.
Some objects have shiny appearance called lustre whereas some materials have dull appearance. For example, gold, silver, copper have shiny appearance whereas paper, wood, rubber have dull appearance.
Hardness and Softness
The materials can be classified on the basis of hardness and softness. Candle, wax, rubber are the examples of soft materials whereas iron, diamond, glass are the examples hard materials.
Some materials are soluble in water whereas others are not. Sugar, common salt, washing soda lemon juice are soluble in water whereas glass, plastic, iron, mustard oil, coconut oil are not soluble in water.
Density is the mass per unit volume of a substance. The substances which sink in the water have higher density than water and the substances which float on the water have lower density than water. Substances like iron, copper, aluminium, silver, gold and glass have higher density than water whereas wood, plastic, ice, oil and petrol have lower density than water.
All the materials have been classified into three groups on the basis of transparency.
Transparent: The materials through which light can pass are called transparent materials. For example, glass, water, air, alcohol, etc.
Translucent: The materials through which light can pass partially are called translucent materials. For example, Butter paper, ground-glass, muddy water, etc.
Opaque: The materials through which light cannot pass are called opaque materials. For example, metals, stones, books, woods, etc.
The substances which are made up of only one kind of atoms or molecules are called pure substances. For example gold, silver, copper, etc.
When two or more than two different substances are mixed up together a mixture is formed. For example, air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and some other gases.
Constituents of a Mixture
The different substances which are present in a mixture are called constituents of the mixture. For example, nitrogen, oxygen, carbon dioxide and many other gases which are present in the air are constituents of air.
Changes Around Us
Changes Around Us
We observe changes around us all the time. Changes may occur in shape, size, mass, density, colour, position, temperature, structure or in composition of a substance. So we can define a change as:
'Transformation in one or more than one physical or chemical properties of a substance is called change'.
Types of Changes
Types of changes on the basis of either the changes can be reversed to bring back the original substance or not:
A change which can be reversed to form the 'original substance' is called reversible change. For example, melting of ice, freezing of water, dissolution of salt in water, increase in temperature of a metal rod, etc.
A change which cannot be reversed to form the 'original substance' called irreversible change. For example, burning of wood, ripening of fruit, turning milk sour, etc.
Types of changes on the basis of either a new substance is formed or not:
The change, in which molecules of a substance do not undergo any change or no new substances are formed, are called physical changes. For example, melting of ice, freezing of water, evaporation of water, dissolution of salt in water.
The change, in which molecules of substance undergo change or new substances are formed, are called chemical changes. For example, burning of paper, rusting of spoliation of food, etc.
Types of changes on the basis of heat absorbed or evolved:
The change in which heat is released. For example, burning of wood.
The change in which heat is absorbed. For example, melting of ice.
Living Organisms and their Habitats
There are a large number of plants in our surroundings. Plants are living things which can make their own food. They are vital for the survival of animals including us. Let's study about the plants in some detail.
Classification of Plants on the Basis of Bearing Flowers
All the plants has been divided into two groups on the basis that either they bear flower or not.
Flowering Plants: The plants, which bear flowers, are called flowering plants. For example, rose, mango, sunflower, grass, lemon, tulsi, peepal, etc.
Non-Flowering Plants: The plants, which do not bear flowers, are called non-flowering plants. For example, ferns, mosses, algae, fungi, etc.
Classification of Plants on the Basis of Size, Nature of Stem and Life-span
Herbs are small plants which have a soft and delicate stem. They have short life-spat. They live for only one or two season. For example, grass, tomato, wheat, paddy, cabbage etc. Banana plant is a herb.
Shrubs are medium sized plants which have hard but not very thick stem. Their lifespan is for many years but less than that of trees. For example, rose, lemon, jasmine, etc.
Trees are tall and big plants which have hard brown thick stem. Their life-span is for many years. For example, mango, neem, palm, coconut, etc.
Climber plants have long, thin and weak stem so they cannot stand upright. They climb up with the help of a support. For example, pea plants, grape vine, glory lily, jasmine, etc.
Creeper plants also have long, thin, and weak stem. Creeper plants do not have special organ for climbing up so they spread out on the ground. For example, strawberry, pumpkin, cucumber, etc.
Parts of a Plant
Root stem, leaves, flowers and fruits are the main parts of plants.
This part of a plant grows below the ground. Root fixes the plant firmly to the soil. It absorbs water and minerals from the soil which are essential for the photosynthesis.
Types of Roots
There are mainly two types of roots: tap root and fibrous root.
Tip root: It consists of a main root called tap root from which a number of branching
Roots arise called lateral roots. For example, mango, radish, mustard, etc.
Fibrous root: It consists of many thin, fibre like roots arising from the base of the stem. For example, grass, wheat, paddy, maize, etc.
Functions of Stem:
It holds the plants upright.
It bears branches, leaves, flowers and fruits.
It transports water from the root to leaves and food from leaves to root.
It is the thin, broad, flat and green part of plants which is attached to stem. Flat green portion of leaf is called more...
When we move our body parts like mouth, head, arms, hand and finger, etc. Then our body may remain at the same place. But when we walk by using legs, than we move our whole body from one place to another. The ability of a human being to move its body from one place to another, is called locomotion.
The Skeletal System
The human skeleton or skeletal system is made up of 206 bones. A baby has 300 bones in all But as it grows, some of the bones fuse together or join. Before we learn more about bones and the Joints and where they are joined together, let us take a look at the functions of the skeletal system.
The bones of our body act as a framework or give a shape to our body. Without bones, our body could be a shapeless mass, say like the body of a snail. It is the movements of the bones that helps us bend, run, walk and so on.
Twenty-two bones make up the skull. These are the hardest of all the bones in the body. Some of tee form the cranium, or the cover for the brain. All the bones of the skull except the one forming the lower Jaw are fixed firmly, and cannot move. Only the bone of the lower jaw is capable of movement, which helps us to eat and speak.
Most of the bones of the skull are fixed. Only the lower jaw can move.
The spine also called the vertebral column or backbone, the spine consists of 33 small bones known as vertebrae (singular: vertebra). The vertebrae are hollow at the centre and are joined together form a tube, through which runs the spinal cord.
One of the functions of the vertebral column is to protect the spinal cord. The other functions are to hold the body up and help us bend forward, backward, sideways and twist from the waist.
Running through the centre of the chest is the breastbone or sternum. Joined to it are 10 pairs of strong, flexible bones called ribs. The ribs curve around and join the chest vertebrae at the back, to form a protective cover for the lungs and heart, called the ribcage. Another two pairs of ribs are joined only to the backbone. These are called floating ribs. The ribs are attached to the sternum in such a way as to allow the ribcage to expand when we inhale, or breathe in and contract when we exhale, or breathe out.
The Shoulder Bones
In shoulder bone each collar bone (clavicle) is attached to a shoulder blade (scapula) and to the breastbone.
Motion and Measurement of Distances
The quantities like length, mass, time etc. that can be measured are called physical quantities.
Measurement: It is the comparison of an unknown quantity with a certain fixed quantity of the same kind.
Unit of Measurement: A unit of measurement is a definite magnitude of a physical quantity. For example metre, centimetre, kilometre etc are units of length.
Standard Unit: For the sake of uniformity, scientists all over the world have accepted a system of units called SI system. In the SI System
The unit of length is metre (m).
The unit of mass is kilogram (kg).
The unit of time is second (s).
Other system used are FPS, CGS and MKS.
Multiples and Submultiples of Units
1 centimetre (cm) =10 millimetres
1 decimetre (dm) = 10 centimetres = 100 mm
1 metre (m) = 100 centimetres
1 metre (m) = 1000 millimetres
1 kilometre (km) = 1000 metres
1 gram (g) = 1000 milligrams
1 kilogram (kg) = 1000 grams
1 kilogram (kg) = 1000000 milligrams
1 quintal = 100 kilograms
1 metric ton = 1000 kilograms
1 minute = 60 seconds
1 hour = 60 minutes
1 day = 24 hours
1 year = days
1 century =100 years
1 millennium = 1000 years
If an object changes its position with respect to time, the body is said to be in motion. If an object does not change its position with respect to time. The object is said to be at rest.
Types of Motion
There are different types of motions. Let us know about them.
Rectilinear Motion: Motion in a straight path. For example, ear moving on straight road.
Circular Motion: Motion in a circular path. For example, toy train moving on a circular path.
Periodic Motion: The motion which repeats itself after a regular interval of time. For example, motion of hands of clock.
Rotational Motion: Spinning of an object about a fixed axis. For example, motion giant wheel and rotation of earth.
Electricity and Magnets
Electricity is a form of energy called electrical energy. We can convert electrical energy into various other forms of energies easily.
The path through which electric current can flow is known as electric circuit. A simple electric circuit is made up of a bulb, wire and an electric cell. An electric cell has two terminals: a positive terminal and a negative terminal. A wire is connected from positive terminal to negative terminal of the cell and the bulb is connected to the wire so that current can flow through bulb.
Closed Circuit: When there is no gap in an electric circuit or the normal path of current has not been interrupted, the circuit is known as closed or complete circuit.
Open Circuit: When there is a gap in an electric circuit or the normal path of current has been interrupted, the circuit is known as an open circuit or incomplete circuit.
Conductors and Insulators
The substances which allow electric current to pass through them are called conductors. For example, copper, gold, silver, aluminium, iron, etc. are good conductors of electricity. The substances which do not allow electric current to pass through them are called insulators For example, wood, plastic, paper, rubber, etc. are insulators.
An electric cell is a device which can generate electric current in a closed circuit. It is small and easily portable so it is very useful for us. There are a number of machines like watches, calculators, toys, cars, etc. in which electrical cell is used to produce electric current. Dry cell, button cell, solar cell are the examples of electric cell.
A dry cell is a cylindrical device in which a number of chemicals are stored. It has a metal cap on one side called positive terminal and a metal sheet at other side called negative terminal. It produces electric current from the chemical stored inside it.
An electric bulb is a device which produces light energy using electrical energy. It consists of a glass bulb fixed on a metal case, a thin wire fixed between the two thick wires called filament of the bulb and the gas filled inside the glass bulb. When electric current passes through the filament, it emits light which makes the bulb glow.
Magnet is a substance which attracts magnetic materials such as iron, nickel, steel and cobalt. Magnets are of different shapes and sizes. For example, U-shaped magnate cylindrical magnet, bar magnet, etc. Each magnet has two poles, southpole and north pole.
Magnetic Materials: The materials which are attracted by a magnet are called magnetic materials. For example, iron, nickel, steel more...
Water is an abiotic component of the environment which is essential for the survival of life on the earth. It is present on the earth in all three states solid, liquid and gas. It covers about 71% of the earth surface.
Importance of Water
It is the water which makes life possible on earth. Without water existence of life was not possible on the earth. Therefore, water is very important for all of us.
Water is essential for the survival of life.
Water provides shelter to the large variety of plants and animals.
Plants use water for preparing food.
Water is essential for germination of seeds and their growth.
Uses of Water
Water is used for different purposes in our day to day life.
Water is used for drinking, bathing, cooking and cleaning clothes.
Water is used for irrigation in agriculture.
Water is used in the industries for the production of various substances.
Water is used for the production of electricity.
States of Water
Water is found on earth in all the three states.
Solid: Snow is the solid state of water. When water is cooled, it is converted into ice. This process is known as freezing or solidification.
Liquid: When ice is heated, it is converted into water. This process is known as melting. Condensation is the process by which water vapor cooled down to convert into water.
Gas: Water vapor is gaseous state of water. When liquid water is heated, it gets convened into water vapor. This process is known as evaporation.
The continuous circulation of water from the earth's surface to atmosphere and from the atmosphere back to the earth is called water cycle.
Due to sunlight water from the different sources converts into water vapor. These water vapors rise up in the atmosphere and condense to water drops forming cloud. Then they return back to the surface of earth in the form of rain.
Sources of Water
Oceans, seas, lakes, rivers, ponds, rainwater and ground water are the sources of water.
Rain Water: Rainwater is the purest form of water. It collects on the earth in the form of surface water and underground water.
Surface Water: Water present on the surface of the earth in the form of oceans, seas, rivers, lakes, ponds and streams is called surface water. Ocean contains almost 97% of water present on the earth. But it is saline therefore it is unfit for drinking.
Underground Water: Some of the rainwater seeps through the soil and gathers in the non-porous rocks below. This water is known as underground water.
Conservation of Water
As we have studied earlier water is very important for us. So we must conserve water whenever it is possible. Some ways more...