Just like soil and water, air is also a part of the earth. Gases like hydrogen, oxygen, nitrogen, carbon dioxide and many other gases together form a mixture called air.
Air and some other components form a very thin layer over the earth's surface. This layer is called the atmosphere.
The different gases present in the air have unique properties and play a vital role in the creation and evolution of life.
Air cannot be seen because it is transparent, colourless but it occupies space. When air moves, it is called wind which can be felt.
The blanket of air surrounding the earth is the atmosphere.
As air is a mixture, all the constituent gases have their original properties and they can be recovered separately. One such process of obtaining nitrogen from air includes liquification (cooling) followed by fractional distillation.
Nitrogen makes up the major part of air. It is not required by us directly, but it is used in the form of compounds. It is essential for plant and animal growth and has various other uses.
About one-fifth of air is made up of oxygen. It is required by all living organisms for breathing.
Plants release oxygen into the air through a process called photosynthesis.
The other important constituents of air are carbon dioxide, water vapour and inert gases.
Water vapour plays an important role in the water cycle. The amount of water in the air is a measure of the humidity of that place.
Carbon dioxide is required by plants to prepare their food by the process of (photosynthesis).
Air is also present in soil and water.
Air is necessary for life as we breathe it. Organisms living on land directly consume oxygen from the air.
Oxygen in the air is continuously being used in burning and breathing (respiration), and carbon dioxide is being added to the air.
Green plants absorb carbon dioxide from the air and make food by combining it with water and energy from sunlight with the help of chlorophyll and release oxygen into the air.
Air plays a major role in sailing of boats/communication/wind mills, generation of electricity, water cycle, etc.
Earthworms come out of the soil after heavy rain as they cannot breathe in waterlogged soil.
After heavy downpour, ants also carry their eggs from their anthills to safe places.
Different modes of transport are used to go from one place to another.
In ancient times, people used the length of a foot, the width of a finger, the distance of a step as units of measurement. This caused variation and inaccuracy and a need to develop a uniform system of measurement arose.
Now, the International System of Units (S.I. unit) is followed all over the world.
A unit is a standardized quantity of a physical property, used as a factor to express quantities of that property.
A standard unit is the measurement value which remains the same even when it is measured by anybody at any place.
The standard units of length are millimetre (mm), centimetre (cm), metre (m) and kilometer (km).
The following is the relationship between the units.
Objects which emit light energy by themselves are called luminous bodies.
e.g., the sun, the stars, and glow worms.
The bodies which do not have light energy of their own but reflect the light energy falling on them and hence are visible to us are called non-luminous bodies.
e.g., the moon, objects around us, books, chairs, buildings, trees, etc.
The moon appears bright due to the reflection of sunlight falling on it.
Transparent bodies are substances through which light is propagated easily,
Translucent bodies are substances through which light is propagated partially.
e.g., oil, ground glass, etc.
Opaque bodies are substances through which light is not propagated.
e.g., wood, iron, etc.
Light travels in straight lines.
Smooth surfaces like mirrors form images.
The shadow of an object is formed because of the rectilinear propagation of light. A shadow is the area of darkness formed on the screen, when an opaque body is placed in between the screen and a source of light
A pin hole camera uses the principle of rectilinear propagation of light. It produces a real image which is much smaller than the object and is inverted (upside down).
The returning of a light ray passing through an optical medium into the same medium from the surface of the second medium is called the reflection of light.
The surfaces which reflect light are called reflecting surfaces.
Substances that can attract iron are called magnets.
Substances can be divided into magnetic and non-magnetic substances.
Substances that are attracted by a magnet are called magnetic substances. Usually things made up of iron, nickel or cobalt are magnetic.
Substances that are not attracted by a magnet are called nan-magnetic substances. Paper, plastic and wood are a few examples of non-magnetic substances.
Magnets are divided into two groups - natural and artificial magnets. Magnetite (lodestone) is a naturally occurring magnet.
Artificial magnets can be of many shapes and are commonly used in different articles like electric bells, radio, etc.
The magnetic force or the force of attraction in a magnet is concentrated at the two ends of a magnet. These ends are called poles. They are called the north pole and the south pole.
Properties of magnets
(i) There are always two poles in a magnet placed at opposite ends. This holds true even if we break or cut the magnet into smaller pieces. Each piece
will have two poles.
(ii) When two different magnets are brought closer, like poles repel and unlike poles attract each other.
(iii) A magnet, when suspended freely, always comes to rest in a line along the north-south line of that place.
The bar AB (of iron or steel) to be magnetized is stroked with a bar magnet from one end to the other using the same pole as shown in the figure. This process is repeated for about 50 times.
The end A from where the process starts develops the same polarity as the pole of the magnet stroking and the other end develops the opposite polarity.
Magnets lose their properties when they are heated, hammered or dropped and if they are not stored properly.
Magnetism is widely used to make articles like cassettes, computers, T.V., ATM cards, etc.
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 carnivores 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 hot and humid weather.
Wool fibres are obtained from the hair of animals like sheep, goat, rabbit, yak and camel. Wool is 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. This 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 themself 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 obtain silk yarns then silk yarns are woven to make silk clothes.
The rearing of silkworm for the production of silk fibres is called sericulture.
Jute fibres are obtained from 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 of 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 iron, 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.